PowerPC, Fix-test-gdb.base-store.exp

PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

GDB maintainers:

The gdb.base/store.exp test has five failures on PowerPC.  Part of the
issue is the PowerPC DWARF mapping is not correct on Linux.  The first
patch in this series fixes the PowerPC DWARF mapping.  Once the mapping
was fixed another issue was found with how the signal handlers were
handled on PowerPC.  The issue is on PowerPC the sequence of events for
handling signals is a little different on PowerPC from most other
architectures. 

The first patch fixes the PowerPC DWARF register mapping and the signal
handling issue on PowerPC.  These changes fix three of the five
failures on the store.exp test.

The second patch fixes the remaining issue for the store.exp test.  The
remaining issues are due to handling the 128-bit floating point values.
The 64-bit floating point values are stored in the floating point
registers while the 128-bit floating point values are stored in a VSR. 
The DWARF uses the floating point register numbers for both the 64-bit
and 128-bit floating point values.  The second patch adds a routine to
check if a value is a 128-bit floating point value, if so it then
adjusts the register mapping to point to the VSR registers instead of
the 64-bit floating point registers.

The series of two patches have been tested on PowerPC LE and BE.  The
patches have also been tested on Intel X86-64.  No regression failures
was found.

Please let me know if these patches are acceptable for mainline. 
Thanks.

                             Carl 

[Patch 1/2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

GDB maintainers:

This is the first patch in the series which fixes the DWWARF register
mapping and signal handling issues on PowerPC.

                  Carl

-----------------------------------------------

rs6000, Fix Linux DWARF register mapping

The PowerPC DWARF register mapping is the same for the .eh_frame and
.debug_frame on Linux.  PowerPC uses different mapping for .eh_frame and
.debug_frame on other operating systems.  The current GDB support for
mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum and
rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct for Linux.
The files have some legacy mappings for spe_acc, spefscr, EV which was
removed from GCC in 2017.

This patch adds a two new functions rs6000_linux_dwarf2_reg_to_regnum,
and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c to handle
the DWARF register mappings on Linux.  Function
rs6000_linux_dwarf2_reg_to_regnum is installed for both gdb_dwarf_to_regnum
and gdbarch_stab_reg_to_regnum since the mappings are the same.

The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is updated to
call set_gdbarch_dwarf2_reg_to_regnum map the new function
rs6000_linux_dwarf2_reg_to_regnum for the architecture.  Similarly,
dwarf2_frame_set_adjust_regnum is called to map
rs6000_linux_adjust_frame_regnum into the architecture.

The second issue fixed by this patch is the check for subroutine
process_event_stop_test.  Need to make sure the frame is not the
SIGTRAMP_FRAME.  The sequence of events on most platforms is:

  1) Some code is running when a signal arrives.
  2) The kernel handles the signal and dispatches to the handler.
    ...

However on PowerPC the sequence of events is:

  1) Some code is running when a signal arrives.
  2) The kernel handles the signal and dispatches to the trampoline.
  3) The trampoline performs a normal function call to the handler.
      ...

We want "nexti" to step into, not over, signal handlers invoked
by the kernel.  This is the case most platforms as the kernel puts a
signal trampoline frame onto the stack to handle proper return after the
handler.  However, on some platforms such as PowerPC, the kernel actually
uses a trampoline to handle *invocation* of the handler.

The issue is fixed in function process_event_stop_test by adding a check
that the frame is not a SIGTRAMP_FRAME to the if statement to stop in
a subroutine call.  This prevents GDB from erroneously detecting the
trampoline invocation as a subroutine call.

This patch fixes two regression test failures in gdb.base/store.exp.  It
also fixes two regression failures in gdb.python/py-thread-exited.exp.

Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10 with no
new regressions.
---
 gdb/infrun.c         | 13 ++++++++++
 gdb/ppc-linux-tdep.c | 56 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 4730d290442..922d8a6913d 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -7334,8 +7334,21 @@ process_event_stop_test (struct execution_control_state *ecs)
      initial outermost frame, before sp was valid, would
      have code_addr == &_start.  See the comment in frame_id::operator==
      for more.  */
+
+  /* We want "nexti" to step into, not over, signal handlers invoked
+     by the kernel, therefore this subroutine check should not trigger
+     for a signal handler invocation.  On most platforms, this is already
+     not the case, as the kernel puts a signal trampoline frame onto the
+     stack to handle proper return after the handler, and therefore at this
+     point, the current frame is a grandchild of the step frame, not a
+     child.  However, on some platforms, the kernel actually uses a
+     trampoline to handle *invocation* of the handler.  In that case,
+     when executing the first instruction of the trampoline, this check
+     would erroneously detect the trampoline invocation as a subroutine
+     call.  Fix this by checking for SIGTRAMP_FRAME.  */
   if ((get_stack_frame_id (frame)
        != ecs->event_thread->control.step_stack_frame_id)
+      && get_frame_type (frame) != SIGTRAMP_FRAME
       && ((frame_unwind_caller_id (get_current_frame ())
 	   == ecs->event_thread->control.step_stack_frame_id)
 	  && ((ecs->event_thread->control.step_stack_frame_id
diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index 784dafa59db..7fb90799dff 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -83,6 +83,7 @@
 #include "features/rs6000/powerpc-isa207-vsx64l.c"
 #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
 #include "features/rs6000/powerpc-e500l.c"
+#include "dwarf2/frame.h"
 
 /* Shared library operations for PowerPC-Linux.  */
 static struct target_so_ops powerpc_so_ops;
@@ -2088,6 +2089,52 @@ ppc_linux_displaced_step_prepare  (gdbarch *arch, thread_info *thread,
   return per_inferior->disp_step_buf->prepare (thread, displaced_pc);
 }
 
+/* Convert a Dwarf 2 register number to a GDB register number for Linux.  */
+static int
+rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
+{
+  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
+
+  if (0 <= num && num <= 31)
+    return tdep->ppc_gp0_regnum + num;
+  else if (32 <= num && num <= 63)
+    /* FIXME: jimb/2004-05-05: What should we do when the debug info
+       specifies registers the architecture doesn't have?  Our
+       callers don't check the value we return.  */
+    return tdep->ppc_fp0_regnum + (num - 32);
+  else if (77 <= num && num < 77 + 32)
+    return tdep->ppc_vr0_regnum + (num - 77);
+  else
+    switch (num)
+      {
+      case 65:
+	return tdep->ppc_lr_regnum;
+      case 66:
+	return tdep->ppc_ctr_regnum;
+      case 76:
+	return tdep->ppc_xer_regnum;
+      case 109:
+	return tdep->ppc_vrsave_regnum;
+      case 110:
+	return tdep->ppc_vrsave_regnum - 1; /* vscr */
+      }
+
+  /* Unknown DWARF register number.  */
+  return -1;
+}
+
+/* Translate a .eh_frame register to DWARF register, or adjust a
+   .debug_frame register.  */
+
+
+static int
+rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
+				  int eh_frame_p)
+{
+  /* Linux uses the same numbering for .debug_frame numbering as .eh_frame.  */
+  return num;
+}
+
 static void
 ppc_linux_init_abi (struct gdbarch_info info,
 		    struct gdbarch *gdbarch)
@@ -2135,6 +2182,15 @@ ppc_linux_init_abi (struct gdbarch_info info,
   set_gdbarch_stap_is_single_operand (gdbarch, ppc_stap_is_single_operand);
   set_gdbarch_stap_parse_special_token (gdbarch,
 					ppc_stap_parse_special_token);
+  /* Linux DWARF register mapping is different from the othe OS's.  */
+  set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
+				    rs6000_linux_dwarf2_reg_to_regnum);
+  /* Note on Linux the mapping for the DWARF registers and the stab registers
+     use the same numbers.  Install rs6000_linux_dwarf2_reg_to_regnum for the
+     stab register mappings as well.  */
+  set_gdbarch_stab_reg_to_regnum (gdbarch,
+				    rs6000_linux_dwarf2_reg_to_regnum);
+  dwarf2_frame_set_adjust_regnum (gdbarch, rs6000_linux_adjust_frame_regnum);
 
   if (tdep->wordsize == 4)
     {
-- 
2.37.2

[PATCH 2/2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

GDB maintainers:

This is the second patch which fixes the 128-bit floating point
register mappings.

             Carl 
--------------------------------------------------------
Fix test gdb.base/store.exp

The test currently fails for IEEE 128-bit floating point types.  PowerPC
supports the IBM double 128-bit floating point	format and IEEE 128-bit
format.  The IBM double 128-bit floating point format uses two 64-bit
floating point registers to store the 128-bit value.  The IEEE 128-bit
floating point format stores the value in a single 128-bit vector-scalar
register (vsr).

The various floating point values, 32-bit float, 64-bit double, IBM double
128-bit float and IEEE 128-bit floating point numbers are all mapped to the
DWARF fpr numbers.  The issue is the IEEE 128-bit floating point values are
actually stored in a vsr not the fprs.  This patch changes the register
mapping for the vsrs from the fpr to the vsr registers so the value is
properly accessed by GDB.  The functions rs6000_linux_register_to_value,
rs6000_linux_value_to_register, rs6000_linux_value_from_register check if
the value is an IEEE 128-bit floating point value and adjust the register
number as needed.  The test in function rs6000_convert_register_p is fixed
to so it is only true for floating point values.

This patch fixes three regression tests in gdb.base/store.exp.

The patch has been tested on Power 8 LE/BE, Power 9 LE/BE and Power 10 LE
with no regressions.

Change to inline function
---
 gdb/ppc-linux-tdep.c |  4 +++
 gdb/rs6000-tdep.c    | 66 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index 7fb90799dff..ba646a7230f 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -63,6 +63,7 @@
 #include <ctype.h>
 #include "elf-bfd.h"
 #include "producer.h"
+#include "target-float.h"
 
 #include "features/rs6000/powerpc-32l.c"
 #include "features/rs6000/powerpc-altivec32l.c"
@@ -2101,6 +2102,9 @@ rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
     /* FIXME: jimb/2004-05-05: What should we do when the debug info
        specifies registers the architecture doesn't have?  Our
        callers don't check the value we return.  */
+    /* Map dwarf register numbers for floating point, double, IBM double and
+       IEEE 128-bit floating point to the fpr range.  Will have to fix the
+       mapping for the IEEE 128-bit register numbers later.  */
     return tdep->ppc_fp0_regnum + (num - 32);
   else if (77 <= num && num < 77 + 32)
     return tdep->ppc_vr0_regnum + (num - 77);
diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
index 23397d037ae..ada9cea3353 100644
--- a/gdb/rs6000-tdep.c
+++ b/gdb/rs6000-tdep.c
@@ -2676,7 +2676,25 @@ rs6000_convert_register_p (struct gdbarch *gdbarch, int regnum,
 	  && regnum < tdep->ppc_fp0_regnum + ppc_num_fprs
 	  && type->code () == TYPE_CODE_FLT
 	  && (type->length ()
-	      != builtin_type (gdbarch)->builtin_double->length ()));
+	      == builtin_type (gdbarch)->builtin_float->length ()));
+}
+
+static int
+ieee_128_float_regnum_adjust (struct gdbarch *gdbarch, struct type *type,
+			      int regnum)
+{
+  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
+
+  /* If we have the an IEEE 128-bit floating point value, need to map the
+   register number to the corresponding VSR.  */
+  if (tdep->ppc_vsr0_regnum != -1
+      && regnum >= tdep->ppc_fp0_regnum
+      && regnum < (tdep->ppc_fp0_regnum + ppc_num_fprs)
+      && (gdbarch_long_double_format (gdbarch) == floatformats_ieee_quad)
+      && (type->length() == 16))
+    regnum = regnum - tdep->ppc_fp0_regnum + tdep->ppc_vsr0_regnum;
+
+  return regnum;
 }
 
 static int
@@ -2691,6 +2709,10 @@ rs6000_register_to_value (frame_info_ptr frame,
   
   gdb_assert (type->code () == TYPE_CODE_FLT);
 
+  /* We have an IEEE 128-bit float need to change regnum mapping from
+     fpr to vsr.  */
+  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
+
   if (!get_frame_register_bytes (frame, regnum, 0,
 				 gdb::make_array_view (from,
 						       register_size (gdbarch,
@@ -2715,11 +2737,52 @@ rs6000_value_to_register (frame_info_ptr frame,
 
   gdb_assert (type->code () == TYPE_CODE_FLT);
 
+  /* We have an IEEE 128-bit float need to change regnum mapping from
+     fpr to vsr.  */
+  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
+
   target_float_convert (from, type,
 			to, builtin_type (gdbarch)->builtin_double);
   put_frame_register (frame, regnum, to);
 }
 
+static struct value *
+rs6000_value_from_register (struct gdbarch *gdbarch, struct type *type,
+			    int regnum, struct frame_id frame_id)
+{
+  int len = type->length ();
+  struct value *value = value::allocate (type);
+  frame_info_ptr frame;
+
+  /* We have an IEEE 128-bit float need to change regnum mapping from
+     fpr to vsr.  */
+  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
+
+  value->set_lval (lval_register);
+  frame = frame_find_by_id (frame_id);
+
+  if (frame == NULL)
+    frame_id = null_frame_id;
+  else
+    frame_id = get_frame_id (get_next_frame_sentinel_okay (frame));
+
+  VALUE_NEXT_FRAME_ID (value) = frame_id;
+  VALUE_REGNUM (value) = regnum;
+
+  /* Any structure stored in more than one register will always be
+     an integral number of registers.  Otherwise, you need to do
+     some fiddling with the last register copied here for little
+     endian machines.  */
+  if (type_byte_order (type) == BFD_ENDIAN_BIG
+      && len < register_size (gdbarch, regnum))
+    /* Big-endian, and we want less than full size.  */
+    value->set_offset (register_size (gdbarch, regnum) - len);
+  else
+    value->set_offset (0);
+
+  return value;
+}
+
  /* The type of a function that moves the value of REG between CACHE
     or BUF --- in either direction.  */
 typedef enum register_status (*move_ev_register_func) (struct regcache *,
@@ -8337,6 +8400,7 @@ rs6000_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_gdbarch_convert_register_p (gdbarch, rs6000_convert_register_p);
   set_gdbarch_register_to_value (gdbarch, rs6000_register_to_value);
   set_gdbarch_value_to_register (gdbarch, rs6000_value_to_register);
+  set_gdbarch_value_from_register (gdbarch, rs6000_value_from_register);
 
   set_gdbarch_stab_reg_to_regnum (gdbarch, rs6000_stab_reg_to_regnum);
   set_gdbarch_dwarf2_reg_to_regnum (gdbarch, rs6000_dwarf2_reg_to_regnum);
-- 
2.37.2

Re: [Patch 1/2] PowerPC, Fix-test-gdb.base-store.exp

[Keith Seitz]

Carl Love wrote:

> This patch fixes two regression test failures in gdb.base/store.exp.  It
> also fixes two regression failures in gdb.python/py-thread-exited.exp.

I did not notice any failures on HEAD in this test? But I also don't see
any new regressions in any test with your patch.  Just FAIL -> PASS.

> Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10 with no
> new regressions.

I've read through this patch (and tested it), and I only have a few very
trivial fixes to request.  I don't think there's any reason to repost to
fix a couple of typos, so just await a proper maintainers approval and
commit with that approval.

I don't know this code sufficiently well to give a proper approval, but
I did not notice anything egregiously wrong.

Tested-by: Keith Seitz <keiths@redhat.com>

Thanks for the patch!
Keith

---
 gdb/infrun.c         | 13 ++++++++++
 gdb/ppc-linux-tdep.c | 56 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index 784dafa59db..7fb90799dff 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -83,6 +83,7 @@
 #include "features/rs6000/powerpc-isa207-vsx64l.c"
 #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
 #include "features/rs6000/powerpc-e500l.c"
+#include "dwarf2/frame.h"
 
 /* Shared library operations for PowerPC-Linux.  */
 static struct target_so_ops powerpc_so_ops;
@@ -2088,6 +2089,52 @@ ppc_linux_displaced_step_prepare  (gdbarch *arch, thread_info *thread,
   return per_inferior->disp_step_buf->prepare (thread, displaced_pc);
 }
 
+/* Convert a Dwarf 2 register number to a GDB register number for Linux.  */
+static int
+rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
+{
+  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
+
+  if (0 <= num && num <= 31)
+    return tdep->ppc_gp0_regnum + num;
+  else if (32 <= num && num <= 63)
+    /* FIXME: jimb/2004-05-05: What should we do when the debug info
+       specifies registers the architecture doesn't have?  Our
+       callers don't check the value we return.  */
+    return tdep->ppc_fp0_regnum + (num - 32);
+  else if (77 <= num && num < 77 + 32)
+    return tdep->ppc_vr0_regnum + (num - 77);
+  else
+    switch (num)
+      {
+      case 65:
+	return tdep->ppc_lr_regnum;
+      case 66:
+	return tdep->ppc_ctr_regnum;
+      case 76:
+	return tdep->ppc_xer_regnum;
+      case 109:
+	return tdep->ppc_vrsave_regnum;
+      case 110:
+	return tdep->ppc_vrsave_regnum - 1; /* vscr */
+      }
+
+  /* Unknown DWARF register number.  */
+  return -1;
+}
+

The spacing here is inconsistent. In the function above, there is no
newline between the comment and the definition.  Here there are two
newlines:

+/* Translate a .eh_frame register to DWARF register, or adjust a
+   .debug_frame register.  */
+
+
+static int
+rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
+				  int eh_frame_p)
+{
+  /* Linux uses the same numbering for .debug_frame numbering as .eh_frame.  */
+  return num;
+}
+
 static void
 ppc_linux_init_abi (struct gdbarch_info info,
 		    struct gdbarch *gdbarch)
@@ -2135,6 +2182,15 @@ ppc_linux_init_abi (struct gdbarch_info info,
   set_gdbarch_stap_is_single_operand (gdbarch, ppc_stap_is_single_operand);
   set_gdbarch_stap_parse_special_token (gdbarch,
 					ppc_stap_parse_special_token);
+  /* Linux DWARF register mapping is different from the othe OS's.  */

Note the typo, "othe[r]". The correct plural form is "OSes".

+  set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
+				    rs6000_linux_dwarf2_reg_to_regnum);
+  /* Note on Linux the mapping for the DWARF registers and the stab registers
+     use the same numbers.  Install rs6000_linux_dwarf2_reg_to_regnum for the
+     stab register mappings as well.  */
+  set_gdbarch_stab_reg_to_regnum (gdbarch,
+				    rs6000_linux_dwarf2_reg_to_regnum);
+  dwarf2_frame_set_adjust_regnum (gdbarch, rs6000_linux_adjust_frame_regnum);
 
   if (tdep->wordsize == 4)
     {
-- 
2.37.2

Re: [PATCH 2/2] PowerPC, Fix-test-gdb.base-store.exp

[Keith Seitz]

Carl Love wrote:

As in your previous patch, I only have some really trivial nits to point out.
So treat similarly, and thank you for the patch.

> The test currently fails for IEEE 128-bit floating point types.  PowerPC
> supports the IBM double 128-bit floating point	format and IEEE 128-bit

Looks like a tab got inserted above?

> format.  The IBM double 128-bit floating point format uses two 64-bit
> floating point registers to store the 128-bit value.  The IEEE 128-bit
> floating point format stores the value in a single 128-bit vector-scalar
> register (vsr).

> The various floating point values, 32-bit float, 64-bit double, IBM double
> 128-bit float and IEEE 128-bit floating point numbers are all mapped to the
> DWARF fpr numbers.  The issue is the IEEE 128-bit floating point values are
> actually stored in a vsr not the fprs.  This patch changes the register
> mapping for the vsrs from the fpr to the vsr registers so the value is
> properly accessed by GDB.  The functions rs6000_linux_register_to_value,
> rs6000_linux_value_to_register, rs6000_linux_value_from_register check if
> the value is an IEEE 128-bit floating point value and adjust the register
> number as needed.  The test in function rs6000_convert_register_p is fixed
> to so it is only true for floating point values.

"fixed [to] so"

> This patch fixes three regression tests in gdb.base/store.exp.
>
> The patch has been tested on Power 8 LE/BE, Power 9 LE/BE and Power 10 LE
> with no regressions.

Indeed!

Tested-by: Keith Seitz <keiths@redhat.com>

> Change to inline function

Stray line or was there something more to communicate?

Keith
---
 gdb/ppc-linux-tdep.c |  4 +++
 gdb/rs6000-tdep.c    | 66 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 69 insertions(+), 1 deletion(-)

diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index 7fb90799dff..ba646a7230f 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -63,6 +63,7 @@
 #include <ctype.h>
 #include "elf-bfd.h"
 #include "producer.h"
+#include "target-float.h"
 
 #include "features/rs6000/powerpc-32l.c"
 #include "features/rs6000/powerpc-altivec32l.c"
@@ -2101,6 +2102,9 @@ rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
     /* FIXME: jimb/2004-05-05: What should we do when the debug info
        specifies registers the architecture doesn't have?  Our
        callers don't check the value we return.  */
+    /* Map dwarf register numbers for floating point, double, IBM double and
+       IEEE 128-bit floating point to the fpr range.  Will have to fix the
+       mapping for the IEEE 128-bit register numbers later.  */

I suggest rewording this last incomplete sentence to something like: "The mapping
for the IEEE 128-bit register numbers will have to be fixed later."

return tdep->ppc_fp0_regnum + (num - 32);
   else if (77 <= num && num < 77 + 32)
     return tdep->ppc_vr0_regnum + (num - 77);
diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
index 23397d037ae..ada9cea3353 100644
--- a/gdb/rs6000-tdep.c
+++ b/gdb/rs6000-tdep.c
@@ -2676,7 +2676,25 @@ rs6000_convert_register_p (struct gdbarch *gdbarch, int regnum,
 	  && regnum < tdep->ppc_fp0_regnum + ppc_num_fprs
 	  && type->code () == TYPE_CODE_FLT
 	  && (type->length ()
-	      != builtin_type (gdbarch)->builtin_double->length ()));
+	      == builtin_type (gdbarch)->builtin_float->length ()));
+}
+
+static int
+ieee_128_float_regnum_adjust (struct gdbarch *gdbarch, struct type *type,
+			      int regnum)
+{
+  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
+
+  /* If we have the an IEEE 128-bit floating point value, need to map the
+   register number to the corresponding VSR.  */

"If we have the an" --> "If we have an". "need to" --> ""

+  if (tdep->ppc_vsr0_regnum != -1
+      && regnum >= tdep->ppc_fp0_regnum
+      && regnum < (tdep->ppc_fp0_regnum + ppc_num_fprs)
+      && (gdbarch_long_double_format (gdbarch) == floatformats_ieee_quad)
+      && (type->length() == 16))
+    regnum = regnum - tdep->ppc_fp0_regnum + tdep->ppc_vsr0_regnum;
+
+  return regnum;
 }
 
 static int
@@ -2691,6 +2709,10 @@ rs6000_register_to_value (frame_info_ptr frame,
   
   gdb_assert (type->code () == TYPE_CODE_FLT);
 
+  /* We have an IEEE 128-bit float need to change regnum mapping from
+     fpr to vsr.  */
+  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
+

Add "--" before "need". Similarly below in a few spots.

if (!get_frame_register_bytes (frame, regnum, 0,
 				 gdb::make_array_view (from,
 						       register_size (gdbarch,
@@ -2715,11 +2737,52 @@ rs6000_value_to_register (frame_info_ptr frame,
 
   gdb_assert (type->code () == TYPE_CODE_FLT);
 
+  /* We have an IEEE 128-bit float need to change regnum mapping from
+     fpr to vsr.  */
+  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
+
   target_float_convert (from, type,
 			to, builtin_type (gdbarch)->builtin_double);
   put_frame_register (frame, regnum, to);
 }
 
+static struct value *
+rs6000_value_from_register (struct gdbarch *gdbarch, struct type *type,
+			    int regnum, struct frame_id frame_id)
+{
+  int len = type->length ();
+  struct value *value = value::allocate (type);
+  frame_info_ptr frame;
+
+  /* We have an IEEE 128-bit float need to change regnum mapping from
+     fpr to vsr.  */
+  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
+
+  value->set_lval (lval_register);
+  frame = frame_find_by_id (frame_id);
+
+  if (frame == NULL)
+    frame_id = null_frame_id;
+  else
+    frame_id = get_frame_id (get_next_frame_sentinel_okay (frame));
+
+  VALUE_NEXT_FRAME_ID (value) = frame_id;
+  VALUE_REGNUM (value) = regnum;
+
+  /* Any structure stored in more than one register will always be
+     an integral number of registers.  Otherwise, you need to do
+     some fiddling with the last register copied here for little
+     endian machines.  */
+  if (type_byte_order (type) == BFD_ENDIAN_BIG
+      && len < register_size (gdbarch, regnum))
+    /* Big-endian, and we want less than full size.  */
+    value->set_offset (register_size (gdbarch, regnum) - len);
+  else
+    value->set_offset (0);
+
+  return value;
+}
+
  /* The type of a function that moves the value of REG between CACHE
     or BUF --- in either direction.  */
 typedef enum register_status (*move_ev_register_func) (struct regcache *,
@@ -8337,6 +8400,7 @@ rs6000_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_gdbarch_convert_register_p (gdbarch, rs6000_convert_register_p);
   set_gdbarch_register_to_value (gdbarch, rs6000_register_to_value);
   set_gdbarch_value_to_register (gdbarch, rs6000_value_to_register);
+  set_gdbarch_value_from_register (gdbarch, rs6000_value_from_register);
 
   set_gdbarch_stab_reg_to_regnum (gdbarch, rs6000_stab_reg_to_regnum);
   set_gdbarch_dwarf2_reg_to_regnum (gdbarch, rs6000_dwarf2_reg_to_regnum);
-- 
2.37.2

RE: [Patch 1/2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

Keith:

Thanks for the review.  I have fixed the typos as noted below.

                 Carl 
----------

On Fri, 2023-10-13 at 13:34 -0700, Keith Seitz wrote:
> Carl Love wrote:
> 
> > This patch fixes two regression test failures in
> > gdb.base/store.exp.  It
> > also fixes two regression failures in gdb.python/py-thread-
> > exited.exp.
> 
> I did not notice any failures on HEAD in this test? But I also don't
> see
> any new regressions in any test with your patch.  Just FAIL -> PASS.
> 
> > Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10
> > with no
> > new regressions.
> 
> I've read through this patch (and tested it), and I only have a few
> very
> trivial fixes to request.  I don't think there's any reason to repost
> to
> fix a couple of typos, so just await a proper maintainers approval
> and
> commit with that approval.
> 
> I don't know this code sufficiently well to give a proper approval,
> but
> I did not notice anything egregiously wrong.
> 
> Tested-by: Keith Seitz <keiths@redhat.com>
> 
> Thanks for the patch!
> Keith
> 
> ---
>  gdb/infrun.c         | 13 ++++++++++
>  gdb/ppc-linux-tdep.c | 56
> ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 69 insertions(+)
> 
> diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> index 784dafa59db..7fb90799dff 100644
> --- a/gdb/ppc-linux-tdep.c
> +++ b/gdb/ppc-linux-tdep.c
> @@ -83,6 +83,7 @@
>  #include "features/rs6000/powerpc-isa207-vsx64l.c"
>  #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
>  #include "features/rs6000/powerpc-e500l.c"
> +#include "dwarf2/frame.h"
>  
>  /* Shared library operations for PowerPC-Linux.  */
>  static struct target_so_ops powerpc_so_ops;
> @@ -2088,6 +2089,52 @@ ppc_linux_displaced_step_prepare  (gdbarch
> *arch, thread_info *thread,
>    return per_inferior->disp_step_buf->prepare (thread,
> displaced_pc);
>  }
>  
> +/* Convert a Dwarf 2 register number to a GDB register number for
> Linux.  */
> +static int
> +rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
> +{
> +  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
> +
> +  if (0 <= num && num <= 31)
> +    return tdep->ppc_gp0_regnum + num;
> +  else if (32 <= num && num <= 63)
> +    /* FIXME: jimb/2004-05-05: What should we do when the debug info
> +       specifies registers the architecture doesn't have?  Our
> +       callers don't check the value we return.  */
> +    return tdep->ppc_fp0_regnum + (num - 32);
> +  else if (77 <= num && num < 77 + 32)
> +    return tdep->ppc_vr0_regnum + (num - 77);
> +  else
> +    switch (num)
> +      {
> +      case 65:
> +	return tdep->ppc_lr_regnum;
> +      case 66:
> +	return tdep->ppc_ctr_regnum;
> +      case 76:
> +	return tdep->ppc_xer_regnum;
> +      case 109:
> +	return tdep->ppc_vrsave_regnum;
> +      case 110:
> +	return tdep->ppc_vrsave_regnum - 1; /* vscr */
> +      }
> +
> +  /* Unknown DWARF register number.  */
> +  return -1;
> +}
> +
> 
> The spacing here is inconsistent. In the function above, there is no
> newline between the comment and the definition.  Here there are two
> newlines:

Added a blank line between comment and
rs6000_linux_dwarf2_reg_to_regnum function definition.

> 
> +/* Translate a .eh_frame register to DWARF register, or adjust a
> +   .debug_frame register.  */
> +
> +

Removed the extra line.

> +static int
> +rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
> +				  int eh_frame_p)
> +{
> +  /* Linux uses the same numbering for .debug_frame numbering as
> .eh_frame.  */
> +  return num;
> +}
> +
>  static void
>  ppc_linux_init_abi (struct gdbarch_info info,
>  		    struct gdbarch *gdbarch)
> @@ -2135,6 +2182,15 @@ ppc_linux_init_abi (struct gdbarch_info info,
>    set_gdbarch_stap_is_single_operand (gdbarch,
> ppc_stap_is_single_operand);
>    set_gdbarch_stap_parse_special_token (gdbarch,
>  					ppc_stap_parse_special_token);
> +  /* Linux DWARF register mapping is different from the othe
> OS's.  */
> 
> Note the typo, "othe[r]". The correct plural form is "OSes".

Ah, thanks for catching the missing r and the spelling error.  Fixed.

> 
> +  set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  /* Note on Linux the mapping for the DWARF registers and the stab
> registers
> +     use the same numbers.  Install
> rs6000_linux_dwarf2_reg_to_regnum for the
> +     stab register mappings as well.  */
> +  set_gdbarch_stab_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  dwarf2_frame_set_adjust_regnum (gdbarch,
> rs6000_linux_adjust_frame_regnum);
>  
>    if (tdep->wordsize == 4)
>      {

RE: [PATCH 2/2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

Keith:

Thanks for catching the typos.  I have fixed them locally for now as
noted below.

                      Carl
--------------

On Fri, 2023-10-13 at 13:35 -0700, Keith Seitz wrote:
> Carl Love wrote:
> 
> As in your previous patch, I only have some really trivial nits to
> point out.
> So treat similarly, and thank you for the patch.
> 
> > The test currently fails for IEEE 128-bit floating point
> > types.  PowerPC
> > supports the IBM double 128-bit floating point	format and IEEE
> > 128-bit
> 
> Looks like a tab got inserted above?

Yea, Git gui doesn't show tabs in the window.  Fixed
> 
> > format.  The IBM double 128-bit floating point format uses two 64-
> > bit
> > floating point registers to store the 128-bit value.  The IEEE 128-
> > bit
> > floating point format stores the value in a single 128-bit vector-
> > scalar
> > register (vsr).
> > The various floating point values, 32-bit float, 64-bit double, IBM
> > double
> > 128-bit float and IEEE 128-bit floating point numbers are all
> > mapped to the
> > DWARF fpr numbers.  The issue is the IEEE 128-bit floating point
> > values are
> > actually stored in a vsr not the fprs.  This patch changes the
> > register
> > mapping for the vsrs from the fpr to the vsr registers so the value
> > is
> > properly accessed by GDB.  The functions
> > rs6000_linux_register_to_value,
> > rs6000_linux_value_to_register, rs6000_linux_value_from_register
> > check if
> > the value is an IEEE 128-bit floating point value and adjust the
> > register
> > number as needed.  The test in function rs6000_convert_register_p
> > is fixed
> > to so it is only true for floating point values.
> 
> "fixed [to] so"
> 
Looks like the "to" didn't get cleanup in the last re-write.  Changed
"to so it" to "so it".


> > This patch fixes three regression tests in gdb.base/store.exp.
> > 
> > The patch has been tested on Power 8 LE/BE, Power 9 LE/BE and Power
> > 10 LE
> > with no regressions.
> 
> Indeed!
> 
> Tested-by: Keith Seitz <keiths@redhat.com>
> 
> > Change to inline function
> 
> Stray line or was there something more to communicate?

Stray line, got missed in the last edit.  Removed.  Thanks.

> 
> Keith
> ---
>  gdb/ppc-linux-tdep.c |  4 +++
>  gdb/rs6000-tdep.c    | 66
> +++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 69 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> index 7fb90799dff..ba646a7230f 100644
> --- a/gdb/ppc-linux-tdep.c
> +++ b/gdb/ppc-linux-tdep.c
> @@ -63,6 +63,7 @@
>  #include <ctype.h>
>  #include "elf-bfd.h"
>  #include "producer.h"
> +#include "target-float.h"
>  
>  #include "features/rs6000/powerpc-32l.c"
>  #include "features/rs6000/powerpc-altivec32l.c"
> @@ -2101,6 +2102,9 @@ rs6000_linux_dwarf2_reg_to_regnum (struct
> gdbarch *gdbarch, int num)
>      /* FIXME: jimb/2004-05-05: What should we do when the debug info
>         specifies registers the architecture doesn't have?  Our
>         callers don't check the value we return.  */
> +    /* Map dwarf register numbers for floating point, double, IBM
> double and
> +       IEEE 128-bit floating point to the fpr range.  Will have to
> fix the
> +       mapping for the IEEE 128-bit register numbers later.  */
> 
> I suggest rewording this last incomplete sentence to something like:
> "The mapping
> for the IEEE 128-bit register numbers will have to be fixed later."
> 
> return tdep->ppc_fp0_regnum + (num - 32);
>    else if (77 <= num && num < 77 + 32)
>      return tdep->ppc_vr0_regnum + (num - 77);
> diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
> index 23397d037ae..ada9cea3353 100644
> --- a/gdb/rs6000-tdep.c
> +++ b/gdb/rs6000-tdep.c
> @@ -2676,7 +2676,25 @@ rs6000_convert_register_p (struct gdbarch
> *gdbarch, int regnum,
>  	  && regnum < tdep->ppc_fp0_regnum + ppc_num_fprs
>  	  && type->code () == TYPE_CODE_FLT
>  	  && (type->length ()
> -	      != builtin_type (gdbarch)->builtin_double->length ()));
> +	      == builtin_type (gdbarch)->builtin_float->length ()));
> +}
> +
> +static int
> +ieee_128_float_regnum_adjust (struct gdbarch *gdbarch, struct type
> *type,
> +			      int regnum)
> +{
> +  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
> +
> +  /* If we have the an IEEE 128-bit floating point value, need to
> map the
> +   register number to the corresponding VSR.  */
> 
> "If we have the an" --> "If we have an". "need to" --> ""
> 
> +  if (tdep->ppc_vsr0_regnum != -1
> +      && regnum >= tdep->ppc_fp0_regnum
> +      && regnum < (tdep->ppc_fp0_regnum + ppc_num_fprs)
> +      && (gdbarch_long_double_format (gdbarch) ==
> floatformats_ieee_quad)
> +      && (type->length() == 16))
> +    regnum = regnum - tdep->ppc_fp0_regnum + tdep->ppc_vsr0_regnum;
> +
> +  return regnum;
>  }
>  
>  static int
> @@ -2691,6 +2709,10 @@ rs6000_register_to_value (frame_info_ptr
> frame,
>    
>    gdb_assert (type->code () == TYPE_CODE_FLT);
>  
> +  /* We have an IEEE 128-bit float need to change regnum mapping
> from
> +     fpr to vsr.  */
> +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> +
> 
> Add "--" before "need". Similarly below in a few spots.

Fixed.

> 
> if (!get_frame_register_bytes (frame, regnum, 0,
>  				 gdb::make_array_view (from,
>  						       register_size
> (gdbarch,
> @@ -2715,11 +2737,52 @@ rs6000_value_to_register (frame_info_ptr
> frame,
>  
>    gdb_assert (type->code () == TYPE_CODE_FLT);
>  
> +  /* We have an IEEE 128-bit float need to change regnum mapping
> from

Added "--"  before "need".
> +     fpr to vsr.  */
> +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> +
>    target_float_convert (from, type,
>  			to, builtin_type (gdbarch)->builtin_double);
>    put_frame_register (frame, regnum, to);
>  }
>  
> +static struct value *
> +rs6000_value_from_register (struct gdbarch *gdbarch, struct type
> *type,
> +			    int regnum, struct frame_id frame_id)
> +{
> +  int len = type->length ();
> +  struct value *value = value::allocate (type);
> +  frame_info_ptr frame;
> +
> +  /* We have an IEEE 128-bit float need to
> change regnum mapping from

Added "--"  before "need".

> +     fpr to vsr.  */
> +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> +
> +  value->set_lval (lval_register);
> +  frame = frame_find_by_id (frame_id);
> +
> +  if (frame == NULL)
> +    frame_id = null_frame_id;
> +  else
> +    frame_id = get_frame_id (get_next_frame_sentinel_okay (frame));
> +
> +  VALUE_NEXT_FRAME_ID (value) = frame_id;
> +  VALUE_REGNUM (value) = regnum;
> +
> +  /* Any structure stored in more than one register will always be
> +     an integral number of registers.  Otherwise, you need to do
> +     some fiddling with the last register copied here for little
> +     endian machines.  */
> +  if (type_byte_order (type) == BFD_ENDIAN_BIG
> +      && len < register_size (gdbarch, regnum))
> +    /* Big-endian, and we want less than full size.  */
> +    value->set_offset (register_size (gdbarch, regnum) - len);
> +  else
> +    value->set_offset (0);
> +
> +  return value;
> +}
> +
>   /* The type of a function that moves the value of REG between CACHE
>      or BUF --- in either direction.  */
>  typedef enum register_status (*move_ev_register_func) (struct
> regcache *,
> @@ -8337,6 +8400,7 @@ rs6000_gdbarch_init (struct gdbarch_info info,
> struct gdbarch_list *arches)
>    set_gdbarch_convert_register_p (gdbarch,
> rs6000_convert_register_p);
>    set_gdbarch_register_to_value (gdbarch, rs6000_register_to_value);
>    set_gdbarch_value_to_register (gdbarch, rs6000_value_to_register);
> +  set_gdbarch_value_from_register (gdbarch,
> rs6000_value_from_register);
>  
>    set_gdbarch_stab_reg_to_regnum (gdbarch,
> rs6000_stab_reg_to_regnum);
>    set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
> rs6000_dwarf2_reg_to_regnum);

RE: [Patch 1/2] PowerPC, Fix-test-gdb.base-store.exp

[Ulrich Weigand]

Carl Love <cel@us.ibm.com> wrote:

>Thanks for the review.  I have fixed the typos as noted below.

This patch (including fixed for the issues pointed out by
Keith) is OK.

Thanks,
Ulrich

RE: [PATCH 2/2] PowerPC, Fix-test-gdb.base-store.exp

[Ulrich Weigand]

Carl Love <cel@us.ibm.com> wrote:

>Thanks for catching the typos.  I have fixed them locally for now as
>noted below.

This patch (including fixed for the issues pointed out by
Keith) is OK.

Thanks,
Ulrich

Re: [Patch 1/2] PowerPC, Fix-test-gdb.base-store.exp

[Andrew Burgess]

Carl Love <cel@us.ibm.com> writes:

> GDB maintainers:
>
> This is the first patch in the series which fixes the DWWARF register
> mapping and signal handling issues on PowerPC.
>
>                   Carl
>
> -----------------------------------------------
>
> rs6000, Fix Linux DWARF register mapping
>
> The PowerPC DWARF register mapping is the same for the .eh_frame and
> .debug_frame on Linux.  PowerPC uses different mapping for .eh_frame and
> .debug_frame on other operating systems.  The current GDB support for
> mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum and
> rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct for Linux.
> The files have some legacy mappings for spe_acc, spefscr, EV which was
> removed from GCC in 2017.
>
> This patch adds a two new functions rs6000_linux_dwarf2_reg_to_regnum,
> and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c to handle
> the DWARF register mappings on Linux.  Function
> rs6000_linux_dwarf2_reg_to_regnum is installed for both gdb_dwarf_to_regnum
> and gdbarch_stab_reg_to_regnum since the mappings are the same.
>
> The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is updated to
> call set_gdbarch_dwarf2_reg_to_regnum map the new function
> rs6000_linux_dwarf2_reg_to_regnum for the architecture.  Similarly,
> dwarf2_frame_set_adjust_regnum is called to map
> rs6000_linux_adjust_frame_regnum into the architecture.
>
> The second issue fixed by this patch is the check for subroutine
> process_event_stop_test.  Need to make sure the frame is not the
> SIGTRAMP_FRAME.  The sequence of events on most platforms is:

Usually for GDB we avoid bundling unrelated changes into a single
commit.  Each commit should address one self contained issue (as far as
possible).

I really struggling to see any connection between the two fixes you have
here.

>
>   1) Some code is running when a signal arrives.
>   2) The kernel handles the signal and dispatches to the handler.
>     ...
>
> However on PowerPC the sequence of events is:
>
>   1) Some code is running when a signal arrives.
>   2) The kernel handles the signal and dispatches to the trampoline.
>   3) The trampoline performs a normal function call to the handler.
>       ...
>
> We want "nexti" to step into, not over, signal handlers invoked
> by the kernel.  This is the case most platforms as the kernel puts a
> signal trampoline frame onto the stack to handle proper return after the
> handler.  However, on some platforms such as PowerPC, the kernel actually
> uses a trampoline to handle *invocation* of the handler.
>
> The issue is fixed in function process_event_stop_test by adding a check
> that the frame is not a SIGTRAMP_FRAME to the if statement to stop in
> a subroutine call.  This prevents GDB from erroneously detecting the
> trampoline invocation as a subroutine call.
>
> This patch fixes two regression test failures in gdb.base/store.exp.  It
> also fixes two regression failures in gdb.python/py-thread-exited.exp.

On the one random PPC box I tried this patch on, I'm not seeing any
failures in gdb.python/py-thread-exited.exp either before, or after this
commit.

Which tests in gdb.python/py-thread-exited.exp are you seeing as broken?
And which of the two fixes in this commit fix the problems you're seeing?

>
> Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10 with no
> new regressions.
> ---
>  gdb/infrun.c         | 13 ++++++++++
>  gdb/ppc-linux-tdep.c | 56 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 69 insertions(+)
>
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 4730d290442..922d8a6913d 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -7334,8 +7334,21 @@ process_event_stop_test (struct execution_control_state *ecs)
>       initial outermost frame, before sp was valid, would
>       have code_addr == &_start.  See the comment in frame_id::operator==
>       for more.  */
> +
> +  /* We want "nexti" to step into, not over, signal handlers invoked
> +     by the kernel, therefore this subroutine check should not trigger
> +     for a signal handler invocation.  On most platforms, this is already
> +     not the case, as the kernel puts a signal trampoline frame onto the
> +     stack to handle proper return after the handler, and therefore at this
> +     point, the current frame is a grandchild of the step frame, not a
> +     child.  However, on some platforms, the kernel actually uses a
> +     trampoline to handle *invocation* of the handler.  In that case,
> +     when executing the first instruction of the trampoline, this check
> +     would erroneously detect the trampoline invocation as a subroutine
> +     call.  Fix this by checking for SIGTRAMP_FRAME.  */
>    if ((get_stack_frame_id (frame)
>         != ecs->event_thread->control.step_stack_frame_id)
> +      && get_frame_type (frame) != SIGTRAMP_FRAME
>        && ((frame_unwind_caller_id (get_current_frame ())
>  	   == ecs->event_thread->control.step_stack_frame_id)
>  	  && ((ecs->event_thread->control.step_stack_frame_id
> diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> index 784dafa59db..7fb90799dff 100644
> --- a/gdb/ppc-linux-tdep.c
> +++ b/gdb/ppc-linux-tdep.c
> @@ -83,6 +83,7 @@
>  #include "features/rs6000/powerpc-isa207-vsx64l.c"
>  #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
>  #include "features/rs6000/powerpc-e500l.c"
> +#include "dwarf2/frame.h"
>  
>  /* Shared library operations for PowerPC-Linux.  */
>  static struct target_so_ops powerpc_so_ops;
> @@ -2088,6 +2089,52 @@ ppc_linux_displaced_step_prepare  (gdbarch *arch, thread_info *thread,
>    return per_inferior->disp_step_buf->prepare (thread, displaced_pc);
>  }
>  
> +/* Convert a Dwarf 2 register number to a GDB register number for Linux.  */
> +static int
> +rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
> +{
> +  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
> +
> +  if (0 <= num && num <= 31)
> +    return tdep->ppc_gp0_regnum + num;
> +  else if (32 <= num && num <= 63)
> +    /* FIXME: jimb/2004-05-05: What should we do when the debug info
> +       specifies registers the architecture doesn't have?  Our
> +       callers don't check the value we return.  */

I see this comment was just copied from else where, but isn't the answer
just: return -1 ?

The comment about the 'return -1' at the trail of this function seems to
suggest that would be the correct thing to do.

I guess I'm asking: do we need to add another copy of this (I think out
of date) fixme?

Thanks,
Andrew

> +    return tdep->ppc_fp0_regnum + (num - 32);
> +  else if (77 <= num && num < 77 + 32)
> +    return tdep->ppc_vr0_regnum + (num - 77);
> +  else
> +    switch (num)
> +      {
> +      case 65:
> +	return tdep->ppc_lr_regnum;
> +      case 66:
> +	return tdep->ppc_ctr_regnum;
> +      case 76:
> +	return tdep->ppc_xer_regnum;
> +      case 109:
> +	return tdep->ppc_vrsave_regnum;
> +      case 110:
> +	return tdep->ppc_vrsave_regnum - 1; /* vscr */
> +      }
> +
> +  /* Unknown DWARF register number.  */
> +  return -1;
> +}
> +
> +/* Translate a .eh_frame register to DWARF register, or adjust a
> +   .debug_frame register.  */
> +
> +
> +static int
> +rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
> +				  int eh_frame_p)
> +{
> +  /* Linux uses the same numbering for .debug_frame numbering as .eh_frame.  */
> +  return num;
> +}
> +
>  static void
>  ppc_linux_init_abi (struct gdbarch_info info,
>  		    struct gdbarch *gdbarch)
> @@ -2135,6 +2182,15 @@ ppc_linux_init_abi (struct gdbarch_info info,
>    set_gdbarch_stap_is_single_operand (gdbarch, ppc_stap_is_single_operand);
>    set_gdbarch_stap_parse_special_token (gdbarch,
>  					ppc_stap_parse_special_token);
> +  /* Linux DWARF register mapping is different from the othe OS's.  */
> +  set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  /* Note on Linux the mapping for the DWARF registers and the stab registers
> +     use the same numbers.  Install rs6000_linux_dwarf2_reg_to_regnum for the
> +     stab register mappings as well.  */
> +  set_gdbarch_stab_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  dwarf2_frame_set_adjust_regnum (gdbarch, rs6000_linux_adjust_frame_regnum);
>  
>    if (tdep->wordsize == 4)
>      {
> -- 
> 2.37.2

Re: [PATCH 2/2] PowerPC, Fix-test-gdb.base-store.exp

[Andrew Burgess]

Carl Love <cel@us.ibm.com> writes:

> GDB maintainers:
>
> This is the second patch which fixes the 128-bit floating point
> register mappings.
>
>              Carl 
> --------------------------------------------------------
> Fix test gdb.base/store.exp
>
> The test currently fails for IEEE 128-bit floating point types.  PowerPC
> supports the IBM double 128-bit floating point	format and IEEE 128-bit
> format.  The IBM double 128-bit floating point format uses two 64-bit
> floating point registers to store the 128-bit value.  The IEEE 128-bit
> floating point format stores the value in a single 128-bit vector-scalar
> register (vsr).
>
> The various floating point values, 32-bit float, 64-bit double, IBM double
> 128-bit float and IEEE 128-bit floating point numbers are all mapped to the
> DWARF fpr numbers.  The issue is the IEEE 128-bit floating point values are
> actually stored in a vsr not the fprs.  This patch changes the register
> mapping for the vsrs from the fpr to the vsr registers so the value is
> properly accessed by GDB.  The functions rs6000_linux_register_to_value,
> rs6000_linux_value_to_register, rs6000_linux_value_from_register check if
> the value is an IEEE 128-bit floating point value and adjust the register
> number as needed.  The test in function rs6000_convert_register_p is fixed
> to so it is only true for floating point values.
>
> This patch fixes three regression tests in gdb.base/store.exp.
>
> The patch has been tested on Power 8 LE/BE, Power 9 LE/BE and Power 10 LE
> with no regressions.
>
> Change to inline function
> ---
>  gdb/ppc-linux-tdep.c |  4 +++
>  gdb/rs6000-tdep.c    | 66 +++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 69 insertions(+), 1 deletion(-)
>
> diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> index 7fb90799dff..ba646a7230f 100644
> --- a/gdb/ppc-linux-tdep.c
> +++ b/gdb/ppc-linux-tdep.c
> @@ -63,6 +63,7 @@
>  #include <ctype.h>
>  #include "elf-bfd.h"
>  #include "producer.h"
> +#include "target-float.h"
>  
>  #include "features/rs6000/powerpc-32l.c"
>  #include "features/rs6000/powerpc-altivec32l.c"
> @@ -2101,6 +2102,9 @@ rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
>      /* FIXME: jimb/2004-05-05: What should we do when the debug info
>         specifies registers the architecture doesn't have?  Our
>         callers don't check the value we return.  */
> +    /* Map dwarf register numbers for floating point, double, IBM double and
> +       IEEE 128-bit floating point to the fpr range.  Will have to fix the
> +       mapping for the IEEE 128-bit register numbers later.  */
>      return tdep->ppc_fp0_regnum + (num - 32);
>    else if (77 <= num && num < 77 + 32)
>      return tdep->ppc_vr0_regnum + (num - 77);
> diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
> index 23397d037ae..ada9cea3353 100644
> --- a/gdb/rs6000-tdep.c
> +++ b/gdb/rs6000-tdep.c
> @@ -2676,7 +2676,25 @@ rs6000_convert_register_p (struct gdbarch *gdbarch, int regnum,
>  	  && regnum < tdep->ppc_fp0_regnum + ppc_num_fprs
>  	  && type->code () == TYPE_CODE_FLT
>  	  && (type->length ()
> -	      != builtin_type (gdbarch)->builtin_double->length ()));
> +	      == builtin_type (gdbarch)->builtin_float->length ()));
> +}
> +
> +static int
> +ieee_128_float_regnum_adjust (struct gdbarch *gdbarch, struct type *type,
> +			      int regnum)
> +{
> +  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
> +
> +  /* If we have the an IEEE 128-bit floating point value, need to map the
> +   register number to the corresponding VSR.  */
> +  if (tdep->ppc_vsr0_regnum != -1
> +      && regnum >= tdep->ppc_fp0_regnum
> +      && regnum < (tdep->ppc_fp0_regnum + ppc_num_fprs)
> +      && (gdbarch_long_double_format (gdbarch) == floatformats_ieee_quad)
> +      && (type->length() == 16))
> +    regnum = regnum - tdep->ppc_fp0_regnum + tdep->ppc_vsr0_regnum;
> +
> +  return regnum;
>  }
>  
>  static int
> @@ -2691,6 +2709,10 @@ rs6000_register_to_value (frame_info_ptr frame,
>    
>    gdb_assert (type->code () == TYPE_CODE_FLT);
>  
> +  /* We have an IEEE 128-bit float need to change regnum mapping from
> +     fpr to vsr.  */
> +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> +
>    if (!get_frame_register_bytes (frame, regnum, 0,
>  				 gdb::make_array_view (from,
>  						       register_size (gdbarch,
> @@ -2715,11 +2737,52 @@ rs6000_value_to_register (frame_info_ptr frame,
>  
>    gdb_assert (type->code () == TYPE_CODE_FLT);
>  
> +  /* We have an IEEE 128-bit float need to change regnum mapping from
> +     fpr to vsr.  */
> +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> +
>    target_float_convert (from, type,
>  			to, builtin_type (gdbarch)->builtin_double);
>    put_frame_register (frame, regnum, to);
>  }
>  
> +static struct value *
> +rs6000_value_from_register (struct gdbarch *gdbarch, struct type *type,
> +			    int regnum, struct frame_id frame_id)
> +{
> +  int len = type->length ();
> +  struct value *value = value::allocate (type);
> +  frame_info_ptr frame;
> +
> +  /* We have an IEEE 128-bit float need to change regnum mapping from
> +     fpr to vsr.  */
> +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> +
> +  value->set_lval (lval_register);
> +  frame = frame_find_by_id (frame_id);

You can move the declaration of frame to here:

  frame_info_ptr frame = frame_find_by_id (frame_id);

which is the preferred GDB style these days.

Reviewed-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew

> +
> +  if (frame == NULL)
> +    frame_id = null_frame_id;
> +  else
> +    frame_id = get_frame_id (get_next_frame_sentinel_okay (frame));
> +
> +  VALUE_NEXT_FRAME_ID (value) = frame_id;
> +  VALUE_REGNUM (value) = regnum;
> +
> +  /* Any structure stored in more than one register will always be
> +     an integral number of registers.  Otherwise, you need to do
> +     some fiddling with the last register copied here for little
> +     endian machines.  */
> +  if (type_byte_order (type) == BFD_ENDIAN_BIG
> +      && len < register_size (gdbarch, regnum))
> +    /* Big-endian, and we want less than full size.  */
> +    value->set_offset (register_size (gdbarch, regnum) - len);
> +  else
> +    value->set_offset (0);
> +
> +  return value;
> +}
> +
>   /* The type of a function that moves the value of REG between CACHE
>      or BUF --- in either direction.  */
>  typedef enum register_status (*move_ev_register_func) (struct regcache *,
> @@ -8337,6 +8400,7 @@ rs6000_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>    set_gdbarch_convert_register_p (gdbarch, rs6000_convert_register_p);
>    set_gdbarch_register_to_value (gdbarch, rs6000_register_to_value);
>    set_gdbarch_value_to_register (gdbarch, rs6000_value_to_register);
> +  set_gdbarch_value_from_register (gdbarch, rs6000_value_from_register);
>  
>    set_gdbarch_stab_reg_to_regnum (gdbarch, rs6000_stab_reg_to_regnum);
>    set_gdbarch_dwarf2_reg_to_regnum (gdbarch, rs6000_dwarf2_reg_to_regnum);
> -- 
> 2.37.2

RE: [Patch 1/2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

Andrew:

Thanks for the review and comments.  See responses below.

On Mon, 2023-10-16 at 15:31 +0100, Andrew Burgess wrote:
> Carl Love <cel@us.ibm.com> writes:
> 
> > GDB maintainers:
> > 
> > This is the first patch in the series which fixes the DWWARF
> > register
> > mapping and signal handling issues on PowerPC.
> > 
> >                   Carl
> > 
> > -----------------------------------------------
> > 
> > rs6000, Fix Linux DWARF register mapping
> > 
> > The PowerPC DWARF register mapping is the same for the .eh_frame
> > and
> > .debug_frame on Linux.  PowerPC uses different mapping for
> > .eh_frame and
> > .debug_frame on other operating systems.  The current GDB support
> > for
> > mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum
> > and
> > rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct
> > for Linux.
> > The files have some legacy mappings for spe_acc, spefscr, EV which
> > was
> > removed from GCC in 2017.
> > 
> > This patch adds a two new functions
> > rs6000_linux_dwarf2_reg_to_regnum,
> > and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c
> > to handle
> > the DWARF register mappings on Linux.  Function
> > rs6000_linux_dwarf2_reg_to_regnum is installed for both
> > gdb_dwarf_to_regnum
> > and gdbarch_stab_reg_to_regnum since the mappings are the same.
> > 
> > The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is updated
> > to
> > call set_gdbarch_dwarf2_reg_to_regnum map the new function
> > rs6000_linux_dwarf2_reg_to_regnum for the architecture.  Similarly,
> > dwarf2_frame_set_adjust_regnum is called to map
> > rs6000_linux_adjust_frame_regnum into the architecture.
> > 
> > The second issue fixed by this patch is the check for subroutine
> > process_event_stop_test.  Need to make sure the frame is not the
> > SIGTRAMP_FRAME.  The sequence of events on most platforms is:
> 
> Usually for GDB we avoid bundling unrelated changes into a single
> commit.  Each commit should address one self contained issue (as far
> as
> possible).
> 
> I really struggling to see any connection between the two fixes you
> have
> here.

As mentioned in the commit log, the first patch which fixes the DWARF
register mapping fixes two of the 5 failures seen in store.exp. 
Specifically the patch fixes the issue of GDB not stopping in the
handler which results in the step.exp test failing.  The second patch
then fixes the rest of the issues with the step.exp test.
> 
> >   1) Some code is running when a signal arrives.
> >   2) The kernel handles the signal and dispatches to the handler.
> >     ...
> > 
> > However on PowerPC the sequence of events is:
> > 
> >   1) Some code is running when a signal arrives.
> >   2) The kernel handles the signal and dispatches to the
> > trampoline.
> >   3) The trampoline performs a normal function call to the handler.
> >       ...
> > 
> > We want "nexti" to step into, not over, signal handlers invoked
> > by the kernel.  This is the case most platforms as the kernel puts
> > a
> > signal trampoline frame onto the stack to handle proper return
> > after the
> > handler.  However, on some platforms such as PowerPC, the kernel
> > actually
> > uses a trampoline to handle *invocation* of the handler.
> > 
> > The issue is fixed in function process_event_stop_test by adding a
> > check
> > that the frame is not a SIGTRAMP_FRAME to the if statement to stop
> > in
> > a subroutine call.  This prevents GDB from erroneously detecting
> > the
> > trampoline invocation as a subroutine call.
> > 
> > This patch fixes two regression test failures in
> > gdb.base/store.exp.  It
> > also fixes two regression failures in gdb.python/py-thread-
> > exited.exp.
> 
> On the one random PPC box I tried this patch on, I'm not seeing any
> failures in gdb.python/py-thread-exited.exp either before, or after
> this
> commit.
> 
> Which tests in gdb.python/py-thread-exited.exp are you seeing as
> broken?
> And which of the two fixes in this commit fix the problems you're
> seeing?

The comment about the py-thread-exited.exp should have been removed.  I
found that sometimes that test fails and sometime passes.  I have yet
to dig into it and figure out why the test is inconsistent.  The
inconsistent behavior exists with and without these patches.

I will remove the comment about the gdb.python/py-thread-exited.exp
fixes as that is erroneous.


> 
> > Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10
> > with no
> > new regressions.
> > ---
> >  gdb/infrun.c         | 13 ++++++++++
> >  gdb/ppc-linux-tdep.c | 56
> > ++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 69 insertions(+)
> > 
> > diff --git a/gdb/infrun.c b/gdb/infrun.c
> > index 4730d290442..922d8a6913d 100644
> > --- a/gdb/infrun.c
> > +++ b/gdb/infrun.c
> > @@ -7334,8 +7334,21 @@ process_event_stop_test (struct
> > execution_control_state *ecs)
> >       initial outermost frame, before sp was valid, would
> >       have code_addr == &_start.  See the comment in
> > frame_id::operator==
> >       for more.  */
> > +
> > +  /* We want "nexti" to step into, not over, signal handlers
> > invoked
> > +     by the kernel, therefore this subroutine check should not
> > trigger
> > +     for a signal handler invocation.  On most platforms, this is
> > already
> > +     not the case, as the kernel puts a signal trampoline frame
> > onto the
> > +     stack to handle proper return after the handler, and
> > therefore at this
> > +     point, the current frame is a grandchild of the step frame,
> > not a
> > +     child.  However, on some platforms, the kernel actually uses
> > a
> > +     trampoline to handle *invocation* of the handler.  In that
> > case,
> > +     when executing the first instruction of the trampoline, this
> > check
> > +     would erroneously detect the trampoline invocation as a
> > subroutine
> > +     call.  Fix this by checking for SIGTRAMP_FRAME.  */
> >    if ((get_stack_frame_id (frame)
> >         != ecs->event_thread->control.step_stack_frame_id)
> > +      && get_frame_type (frame) != SIGTRAMP_FRAME
> >        && ((frame_unwind_caller_id (get_current_frame ())
> >  	   == ecs->event_thread->control.step_stack_frame_id)
> >  	  && ((ecs->event_thread->control.step_stack_frame_id
> > diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> > index 784dafa59db..7fb90799dff 100644
> > --- a/gdb/ppc-linux-tdep.c
> > +++ b/gdb/ppc-linux-tdep.c
> > @@ -83,6 +83,7 @@
> >  #include "features/rs6000/powerpc-isa207-vsx64l.c"
> >  #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
> >  #include "features/rs6000/powerpc-e500l.c"
> > +#include "dwarf2/frame.h"
> >  
> >  /* Shared library operations for PowerPC-Linux.  */
> >  static struct target_so_ops powerpc_so_ops;
> > @@ -2088,6 +2089,52 @@ ppc_linux_displaced_step_prepare  (gdbarch
> > *arch, thread_info *thread,
> >    return per_inferior->disp_step_buf->prepare (thread,
> > displaced_pc);
> >  }
> >  
> > +/* Convert a Dwarf 2 register number to a GDB register number for
> > Linux.  */
> > +static int
> > +rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int
> > num)
> > +{
> > +  ppc_gdbarch_tdep *tdep =
> > gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
> > +
> > +  if (0 <= num && num <= 31)
> > +    return tdep->ppc_gp0_regnum + num;
> > +  else if (32 <= num && num <= 63)
> > +    /* FIXME: jimb/2004-05-05: What should we do when the debug
> > info
> > +       specifies registers the architecture doesn't have?  Our
> > +       callers don't check the value we return.  */
> 
> I see this comment was just copied from else where, but isn't the
> answer
> just: return -1 ?
> 
> The comment about the 'return -1' at the trail of this function seems
> to
> suggest that would be the correct thing to do.
> 
> I guess I'm asking: do we need to add another copy of this (I think
> out
> of date) fixme?

Yes, the function is based on rs6000_dwarf2_reg_to_regnum with the
specific changes for the Linux DWARF mappings.  The comment looked out
of date to me, but I left it for consistency with the other two
functions that have the same comment. It would probably be best to
investigate the comment further and update it in all places in a
separate patch. 

Would it be acceptable to leave the comment as is for now, for
consistency sake, and I will work on a separate cleanup patch to
address removing the comment in the original two places and this
additional place?  I will want to look into it a bit more but I think
we can just remove the comment.  But I do want to verify that the
return value is never used first.

                          Carl 

RE: [PATCH 2/2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

Andrew:

On Mon, 2023-10-16 at 15:36 +0100, Andrew Burgess wrote:
> Carl Love <cel@us.ibm.com> writes:
> 
> > GDB maintainers:
> > 
> > This is the second patch which fixes the 128-bit floating point
> > register mappings.
> >  

<snip>
 
> > +static struct value *
> > +rs6000_value_from_register (struct gdbarch *gdbarch, struct type
> > *type,
> > +			    int regnum, struct frame_id frame_id)
> > +{
> > +  int len = type->length ();
> > +  struct value *value = value::allocate (type);
> > +  frame_info_ptr frame;
> > +
> > +  /* We have an IEEE 128-bit float need to change regnum mapping
> > from
> > +     fpr to vsr.  */
> > +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> > +
> > +  value->set_lval (lval_register);
> > +  frame = frame_find_by_id (frame_id);
> 
> You can move the declaration of frame to here:
> 
>   frame_info_ptr frame = frame_find_by_id (frame_id);

OK, fixed.


> 
> which is the preferred GDB style these days.
> 
> Reviewed-By: Andrew Burgess <aburgess@redhat.com>
> 
> Thanks,
> Andrew
> 

RE: [Patch 1/2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

Andrew:

Just wanted to make sure you were OK with response, particularly about
creating a new patch to address the issues with the comment in the code
before I commit the two patches.

Sorry for the slow response.  My email is being migrated from 
cel@us.ibm.com to cel@linux.ibm.com.  There have been some issues with
the migration.  I don't seem to be getting email at the old address but
the new address does seem to work.  So any replies need to include the
new email address.  Thanks.

                  Carl 

On Mon, 2023-10-16 at 08:51 -0700, Carl Love wrote:
> Andrew:
> 
> Thanks for the review and comments.  See responses below.
> 
> On Mon, 2023-10-16 at 15:31 +0100, Andrew Burgess wrote:
> > Carl Love <cel@us.ibm.com> writes:
> > 
> > > GDB maintainers:
> > > 
> > > This is the first patch in the series which fixes the DWWARF
> > > register
> > > mapping and signal handling issues on PowerPC.
> > > 
> > >                   Carl
> > > 
> > > -----------------------------------------------
> > > 
> > > rs6000, Fix Linux DWARF register mapping
> > > 
> > > The PowerPC DWARF register mapping is the same for the .eh_frame
> > > and
> > > .debug_frame on Linux.  PowerPC uses different mapping for
> > > .eh_frame and
> > > .debug_frame on other operating systems.  The current GDB support
> > > for
> > > mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum
> > > and
> > > rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct
> > > for Linux.
> > > The files have some legacy mappings for spe_acc, spefscr, EV
> > > which
> > > was
> > > removed from GCC in 2017.
> > > 
> > > This patch adds a two new functions
> > > rs6000_linux_dwarf2_reg_to_regnum,
> > > and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c
> > > to handle
> > > the DWARF register mappings on Linux.  Function
> > > rs6000_linux_dwarf2_reg_to_regnum is installed for both
> > > gdb_dwarf_to_regnum
> > > and gdbarch_stab_reg_to_regnum since the mappings are the same.
> > > 
> > > The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is
> > > updated
> > > to
> > > call set_gdbarch_dwarf2_reg_to_regnum map the new function
> > > rs6000_linux_dwarf2_reg_to_regnum for the
> > > architecture.  Similarly,
> > > dwarf2_frame_set_adjust_regnum is called to map
> > > rs6000_linux_adjust_frame_regnum into the architecture.
> > > 
> > > The second issue fixed by this patch is the check for subroutine
> > > process_event_stop_test.  Need to make sure the frame is not the
> > > SIGTRAMP_FRAME.  The sequence of events on most platforms is:
> > 
> > Usually for GDB we avoid bundling unrelated changes into a single
> > commit.  Each commit should address one self contained issue (as
> > far
> > as
> > possible).
> > 
> > I really struggling to see any connection between the two fixes you
> > have
> > here.
> 
> As mentioned in the commit log, the first patch which fixes the DWARF
> register mapping fixes two of the 5 failures seen in store.exp. 
> Specifically the patch fixes the issue of GDB not stopping in the
> handler which results in the step.exp test failing.  The second patch
> then fixes the rest of the issues with the step.exp test.
> > >   1) Some code is running when a signal arrives.
> > >   2) The kernel handles the signal and dispatches to the handler.
> > >     ...
> > > 
> > > However on PowerPC the sequence of events is:
> > > 
> > >   1) Some code is running when a signal arrives.
> > >   2) The kernel handles the signal and dispatches to the
> > > trampoline.
> > >   3) The trampoline performs a normal function call to the
> > > handler.
> > >       ...
> > > 
> > > We want "nexti" to step into, not over, signal handlers invoked
> > > by the kernel.  This is the case most platforms as the kernel
> > > puts
> > > a
> > > signal trampoline frame onto the stack to handle proper return
> > > after the
> > > handler.  However, on some platforms such as PowerPC, the kernel
> > > actually
> > > uses a trampoline to handle *invocation* of the handler.
> > > 
> > > The issue is fixed in function process_event_stop_test by adding
> > > a
> > > check
> > > that the frame is not a SIGTRAMP_FRAME to the if statement to
> > > stop
> > > in
> > > a subroutine call.  This prevents GDB from erroneously detecting
> > > the
> > > trampoline invocation as a subroutine call.
> > > 
> > > This patch fixes two regression test failures in
> > > gdb.base/store.exp.  It
> > > also fixes two regression failures in gdb.python/py-thread-
> > > exited.exp.
> > 
> > On the one random PPC box I tried this patch on, I'm not seeing any
> > failures in gdb.python/py-thread-exited.exp either before, or after
> > this
> > commit.
> > 
> > Which tests in gdb.python/py-thread-exited.exp are you seeing as
> > broken?
> > And which of the two fixes in this commit fix the problems you're
> > seeing?
> 
> The comment about the py-thread-exited.exp should have been
> removed.  I
> found that sometimes that test fails and sometime passes.  I have yet
> to dig into it and figure out why the test is inconsistent.  The
> inconsistent behavior exists with and without these patches.
> 
> I will remove the comment about the gdb.python/py-thread-exited.exp
> fixes as that is erroneous.
> 
> 
> > > Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10
> > > with no
> > > new regressions.
> > > ---
> > >  gdb/infrun.c         | 13 ++++++++++
> > >  gdb/ppc-linux-tdep.c | 56
> > > ++++++++++++++++++++++++++++++++++++++++++++
> > >  2 files changed, 69 insertions(+)
> > > 
> > > diff --git a/gdb/infrun.c b/gdb/infrun.c
> > > index 4730d290442..922d8a6913d 100644
> > > --- a/gdb/infrun.c
> > > +++ b/gdb/infrun.c
> > > @@ -7334,8 +7334,21 @@ process_event_stop_test (struct
> > > execution_control_state *ecs)
> > >       initial outermost frame, before sp was valid, would
> > >       have code_addr == &_start.  See the comment in
> > > frame_id::operator==
> > >       for more.  */
> > > +
> > > +  /* We want "nexti" to step into, not over, signal handlers
> > > invoked
> > > +     by the kernel, therefore this subroutine check should not
> > > trigger
> > > +     for a signal handler invocation.  On most platforms, this
> > > is
> > > already
> > > +     not the case, as the kernel puts a signal trampoline frame
> > > onto the
> > > +     stack to handle proper return after the handler, and
> > > therefore at this
> > > +     point, the current frame is a grandchild of the step frame,
> > > not a
> > > +     child.  However, on some platforms, the kernel actually
> > > uses
> > > a
> > > +     trampoline to handle *invocation* of the handler.  In that
> > > case,
> > > +     when executing the first instruction of the trampoline,
> > > this
> > > check
> > > +     would erroneously detect the trampoline invocation as a
> > > subroutine
> > > +     call.  Fix this by checking for SIGTRAMP_FRAME.  */
> > >    if ((get_stack_frame_id (frame)
> > >         != ecs->event_thread->control.step_stack_frame_id)
> > > +      && get_frame_type (frame) != SIGTRAMP_FRAME
> > >        && ((frame_unwind_caller_id (get_current_frame ())
> > >  	   == ecs->event_thread->control.step_stack_frame_id)
> > >  	  && ((ecs->event_thread->control.step_stack_frame_id
> > > diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> > > index 784dafa59db..7fb90799dff 100644
> > > --- a/gdb/ppc-linux-tdep.c
> > > +++ b/gdb/ppc-linux-tdep.c
> > > @@ -83,6 +83,7 @@
> > >  #include "features/rs6000/powerpc-isa207-vsx64l.c"
> > >  #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
> > >  #include "features/rs6000/powerpc-e500l.c"
> > > +#include "dwarf2/frame.h"
> > >  
> > >  /* Shared library operations for PowerPC-Linux.  */
> > >  static struct target_so_ops powerpc_so_ops;
> > > @@ -2088,6 +2089,52 @@ ppc_linux_displaced_step_prepare  (gdbarch
> > > *arch, thread_info *thread,
> > >    return per_inferior->disp_step_buf->prepare (thread,
> > > displaced_pc);
> > >  }
> > >  
> > > +/* Convert a Dwarf 2 register number to a GDB register number
> > > for
> > > Linux.  */
> > > +static int
> > > +rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int
> > > num)
> > > +{
> > > +  ppc_gdbarch_tdep *tdep =
> > > gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
> > > +
> > > +  if (0 <= num && num <= 31)
> > > +    return tdep->ppc_gp0_regnum + num;
> > > +  else if (32 <= num && num <= 63)
> > > +    /* FIXME: jimb/2004-05-05: What should we do when the debug
> > > info
> > > +       specifies registers the architecture doesn't have?  Our
> > > +       callers don't check the value we return.  */
> > 
> > I see this comment was just copied from else where, but isn't the
> > answer
> > just: return -1 ?
> > 
> > The comment about the 'return -1' at the trail of this function
> > seems
> > to
> > suggest that would be the correct thing to do.
> > 
> > I guess I'm asking: do we need to add another copy of this (I think
> > out
> > of date) fixme?
> 
> Yes, the function is based on rs6000_dwarf2_reg_to_regnum with the
> specific changes for the Linux DWARF mappings.  The comment looked
> out
> of date to me, but I left it for consistency with the other two
> functions that have the same comment. It would probably be best to
> investigate the comment further and update it in all places in a
> separate patch. 
> 
> Would it be acceptable to leave the comment as is for now, for
> consistency sake, and I will work on a separate cleanup patch to
> address removing the comment in the original two places and this
> additional place?  I will want to look into it a bit more but I think
> we can just remove the comment.  But I do want to verify that the
> return value is never used first.
> 
>                           Carl 
> 

[PATCH 1/2, ver2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

GDB maintainers:

Ver2, added a missing blank line, removed an extra blank line, fixed
spelling mistakes.  Removed comment in ChangeLog about fixing py-
thread-exited.exp test errors.  Patch just fixes issues with the
store.exp.  Did not change the comment:

> +    /* FIXME: jimb/2004-05-05: What should we do when the debug info
> +       specifies registers the architecture doesn't have?  Our
> +       callers don't check the value we return.  */
  
Will create a new patch to address the comment in all three places in
the source code.

Note, fixing the register mapping fixes two of the five test failures
for the store.exp test.

Patch was retested on Power10.

This is the first patch in the series which fixes the DWWARF register
mapping and signal handling issues on PowerPC.

                  Carl


-------------------------------------------------
Fix Linux DWARF register mapping

The PowerPC DWARF register mapping is the same for the .eh_frame and
.debug_frame on Linux.  PowerPC uses different mapping for .eh_frame and
.debug_frame on other operating systems.  The current GDB support for
mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum and
rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct for Linux.
The files have some legacy mappings for spe_acc, spefscr, EV which was
removed from GCC in 2017.

This patch adds a two new functions rs6000_linux_dwarf2_reg_to_regnum,
and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c to handle
the DWARF register mappings on Linux.  Function
rs6000_linux_dwarf2_reg_to_regnum is installed for both gdb_dwarf_to_regnum
and gdbarch_stab_reg_to_regnum since the mappings are the same.

The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is updated to
call set_gdbarch_dwarf2_reg_to_regnum map the new function
rs6000_linux_dwarf2_reg_to_regnum for the architecture.  Similarly,
dwarf2_frame_set_adjust_regnum is called to map
rs6000_linux_adjust_frame_regnum into the architecture.

The second issue fixed by this patch is the check for subroutine
process_event_stop_test.  Need to make sure the frame is not the
SIGTRAMP_FRAME.  The sequence of events on most platforms is:

  1) Some code is running when a signal arrives.
  2) The kernel handles the signal and dispatches to the handler.
    ...

However on PowerPC the sequence of events is:

  1) Some code is running when a signal arrives.
  2) The kernel handles the signal and dispatches to the trampoline.
  3) The trampoline performs a normal function call to the handler.
      ...

We want "nexti" to step into, not over, signal handlers invoked
by the kernel.  This is the case most platforms as the kernel puts a
signal trampoline frame onto the stack to handle proper return after the
handler.  However, on some platforms such as PowerPC, the kernel actually
uses a trampoline to handle *invocation* of the handler.

The issue is fixed in function process_event_stop_test by adding a check
that the frame is not a SIGTRAMP_FRAME to the if statement to stop in
a subroutine call.  This prevents GDB from erroneously detecting the
trampoline invocation as a subroutine call.

This patch fixes two regression test failures in gdb.base/store.exp.

Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10 with no
new regressions.
---
 gdb/infrun.c         | 13 ++++++++++
 gdb/ppc-linux-tdep.c | 56 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 69 insertions(+)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 4730d290442..922d8a6913d 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -7334,8 +7334,21 @@ process_event_stop_test (struct execution_control_state *ecs)
      initial outermost frame, before sp was valid, would
      have code_addr == &_start.  See the comment in frame_id::operator==
      for more.  */
+
+  /* We want "nexti" to step into, not over, signal handlers invoked
+     by the kernel, therefore this subroutine check should not trigger
+     for a signal handler invocation.  On most platforms, this is already
+     not the case, as the kernel puts a signal trampoline frame onto the
+     stack to handle proper return after the handler, and therefore at this
+     point, the current frame is a grandchild of the step frame, not a
+     child.  However, on some platforms, the kernel actually uses a
+     trampoline to handle *invocation* of the handler.  In that case,
+     when executing the first instruction of the trampoline, this check
+     would erroneously detect the trampoline invocation as a subroutine
+     call.  Fix this by checking for SIGTRAMP_FRAME.  */
   if ((get_stack_frame_id (frame)
        != ecs->event_thread->control.step_stack_frame_id)
+      && get_frame_type (frame) != SIGTRAMP_FRAME
       && ((frame_unwind_caller_id (get_current_frame ())
 	   == ecs->event_thread->control.step_stack_frame_id)
 	  && ((ecs->event_thread->control.step_stack_frame_id
diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index 784dafa59db..dc03430e2af 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -83,6 +83,7 @@
 #include "features/rs6000/powerpc-isa207-vsx64l.c"
 #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
 #include "features/rs6000/powerpc-e500l.c"
+#include "dwarf2/frame.h"
 
 /* Shared library operations for PowerPC-Linux.  */
 static struct target_so_ops powerpc_so_ops;
@@ -2088,6 +2089,52 @@ ppc_linux_displaced_step_prepare  (gdbarch *arch, thread_info *thread,
   return per_inferior->disp_step_buf->prepare (thread, displaced_pc);
 }
 
+/* Convert a Dwarf 2 register number to a GDB register number for Linux.  */
+
+static int
+rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
+{
+  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
+
+  if (0 <= num && num <= 31)
+    return tdep->ppc_gp0_regnum + num;
+  else if (32 <= num && num <= 63)
+    /* FIXME: jimb/2004-05-05: What should we do when the debug info
+       specifies registers the architecture doesn't have?  Our
+       callers don't check the value we return.  */
+    return tdep->ppc_fp0_regnum + (num - 32);
+  else if (77 <= num && num < 77 + 32)
+    return tdep->ppc_vr0_regnum + (num - 77);
+  else
+    switch (num)
+      {
+      case 65:
+	return tdep->ppc_lr_regnum;
+      case 66:
+	return tdep->ppc_ctr_regnum;
+      case 76:
+	return tdep->ppc_xer_regnum;
+      case 109:
+	return tdep->ppc_vrsave_regnum;
+      case 110:
+	return tdep->ppc_vrsave_regnum - 1; /* vscr */
+      }
+
+  /* Unknown DWARF register number.  */
+  return -1;
+}
+
+/* Translate a .eh_frame register to DWARF register, or adjust a
+   .debug_frame register.  */
+
+static int
+rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
+				  int eh_frame_p)
+{
+  /* Linux uses the same numbering for .debug_frame numbering as .eh_frame.  */
+  return num;
+}
+
 static void
 ppc_linux_init_abi (struct gdbarch_info info,
 		    struct gdbarch *gdbarch)
@@ -2135,6 +2182,15 @@ ppc_linux_init_abi (struct gdbarch_info info,
   set_gdbarch_stap_is_single_operand (gdbarch, ppc_stap_is_single_operand);
   set_gdbarch_stap_parse_special_token (gdbarch,
 					ppc_stap_parse_special_token);
+  /* Linux DWARF register mapping is different from the other OSes.  */
+  set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
+				    rs6000_linux_dwarf2_reg_to_regnum);
+  /* Note on Linux the mapping for the DWARF registers and the stab registers
+     use the same numbers.  Install rs6000_linux_dwarf2_reg_to_regnum for the
+     stab register mappings as well.  */
+  set_gdbarch_stab_reg_to_regnum (gdbarch,
+				    rs6000_linux_dwarf2_reg_to_regnum);
+  dwarf2_frame_set_adjust_regnum (gdbarch, rs6000_linux_adjust_frame_regnum);
 
   if (tdep->wordsize == 4)
     {
-- 
2.37.2

[PATCH 2/2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

GDB maintainers:

Ver 2:  In the new function, rs6000_value_from_register, moved the
declaration of frame to where it gets initialized.   Patch was retested
on Power10.

This is the second patch which fixes the 128-bit floating point
register mappings.  This fixes the remaining three issues with the
store.exp test.

             Carl 

-----------------------------------------
rs6000, Fix test gdb.base/store.exp

The test currently fails for IEEE 128-bit floating point types.  PowerPC
supports the IBM double 128-bit floating point format and IEEE 128-bit
format.  The IBM double 128-bit floating point format uses two 64-bit
floating point registers to store the 128-bit value.  The IEEE 128-bit
floating point format stores the value in a single 128-bit vector-scalar
register (vsr).

The various floating point values, 32-bit float, 64-bit double, IBM double
128-bit float and IEEE 128-bit floating point numbers are all mapped to the
DWARF fpr numbers.  The issue is the IEEE 128-bit floating point values are
actually stored in a vsr not the fprs.  This patch changes the register
mapping for the vsrs from the fpr to the vsr registers so the value is
properly accessed by GDB.  The functions rs6000_linux_register_to_value,
rs6000_linux_value_to_register, rs6000_linux_value_from_register check if
the value is an IEEE 128-bit floating point value and adjust the register
number as needed.  The test in function rs6000_convert_register_p is fixed
so it is only true for floating point values.

This patch fixes three regression tests in gdb.base/store.exp.

The patch has been tested on Power 8 LE/BE, Power 9 LE/BE and Power 10 LE
with no regressions.
---
 gdb/ppc-linux-tdep.c |  4 +++
 gdb/rs6000-tdep.c    | 65 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 68 insertions(+), 1 deletion(-)

diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index dc03430e2af..fac56d961cb 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -63,6 +63,7 @@
 #include <ctype.h>
 #include "elf-bfd.h"
 #include "producer.h"
+#include "target-float.h"
 
 #include "features/rs6000/powerpc-32l.c"
 #include "features/rs6000/powerpc-altivec32l.c"
@@ -2102,6 +2103,9 @@ rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
     /* FIXME: jimb/2004-05-05: What should we do when the debug info
        specifies registers the architecture doesn't have?  Our
        callers don't check the value we return.  */
+    /* Map dwarf register numbers for floating point, double, IBM double and
+       IEEE 128-bit floating point to the fpr range.  Will have to fix the
+       mapping for the IEEE 128-bit register numbers later.  */
     return tdep->ppc_fp0_regnum + (num - 32);
   else if (77 <= num && num < 77 + 32)
     return tdep->ppc_vr0_regnum + (num - 77);
diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
index 23397d037ae..186646673f0 100644
--- a/gdb/rs6000-tdep.c
+++ b/gdb/rs6000-tdep.c
@@ -2676,7 +2676,25 @@ rs6000_convert_register_p (struct gdbarch *gdbarch, int regnum,
 	  && regnum < tdep->ppc_fp0_regnum + ppc_num_fprs
 	  && type->code () == TYPE_CODE_FLT
 	  && (type->length ()
-	      != builtin_type (gdbarch)->builtin_double->length ()));
+	      == builtin_type (gdbarch)->builtin_float->length ()));
+}
+
+static int
+ieee_128_float_regnum_adjust (struct gdbarch *gdbarch, struct type *type,
+			      int regnum)
+{
+  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
+
+  /* If we have the an IEEE 128-bit floating point value, need to map the
+   register number to the corresponding VSR.  */
+  if (tdep->ppc_vsr0_regnum != -1
+      && regnum >= tdep->ppc_fp0_regnum
+      && regnum < (tdep->ppc_fp0_regnum + ppc_num_fprs)
+      && (gdbarch_long_double_format (gdbarch) == floatformats_ieee_quad)
+      && (type->length() == 16))
+    regnum = regnum - tdep->ppc_fp0_regnum + tdep->ppc_vsr0_regnum;
+
+  return regnum;
 }
 
 static int
@@ -2691,6 +2709,10 @@ rs6000_register_to_value (frame_info_ptr frame,
   
   gdb_assert (type->code () == TYPE_CODE_FLT);
 
+  /* We have an IEEE 128-bit float -- need to change regnum mapping from
+     fpr to vsr.  */
+  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
+
   if (!get_frame_register_bytes (frame, regnum, 0,
 				 gdb::make_array_view (from,
 						       register_size (gdbarch,
@@ -2715,11 +2737,51 @@ rs6000_value_to_register (frame_info_ptr frame,
 
   gdb_assert (type->code () == TYPE_CODE_FLT);
 
+  /* We have an IEEE 128-bit float -- need to change regnum mapping from
+     fpr to vsr.  */
+  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
+
   target_float_convert (from, type,
 			to, builtin_type (gdbarch)->builtin_double);
   put_frame_register (frame, regnum, to);
 }
 
+static struct value *
+rs6000_value_from_register (struct gdbarch *gdbarch, struct type *type,
+			    int regnum, struct frame_id frame_id)
+{
+  int len = type->length ();
+  struct value *value = value::allocate (type);
+
+  /* We have an IEEE 128-bit float -- need to change regnum mapping from
+     fpr to vsr.  */
+  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
+
+  value->set_lval (lval_register);
+  frame_info_ptr frame = frame_find_by_id (frame_id);
+
+  if (frame == NULL)
+    frame_id = null_frame_id;
+  else
+    frame_id = get_frame_id (get_next_frame_sentinel_okay (frame));
+
+  VALUE_NEXT_FRAME_ID (value) = frame_id;
+  VALUE_REGNUM (value) = regnum;
+
+  /* Any structure stored in more than one register will always be
+     an integral number of registers.  Otherwise, you need to do
+     some fiddling with the last register copied here for little
+     endian machines.  */
+  if (type_byte_order (type) == BFD_ENDIAN_BIG
+      && len < register_size (gdbarch, regnum))
+    /* Big-endian, and we want less than full size.  */
+    value->set_offset (register_size (gdbarch, regnum) - len);
+  else
+    value->set_offset (0);
+
+  return value;
+}
+
  /* The type of a function that moves the value of REG between CACHE
     or BUF --- in either direction.  */
 typedef enum register_status (*move_ev_register_func) (struct regcache *,
@@ -8337,6 +8399,7 @@ rs6000_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   set_gdbarch_convert_register_p (gdbarch, rs6000_convert_register_p);
   set_gdbarch_register_to_value (gdbarch, rs6000_register_to_value);
   set_gdbarch_value_to_register (gdbarch, rs6000_value_to_register);
+  set_gdbarch_value_from_register (gdbarch, rs6000_value_from_register);
 
   set_gdbarch_stab_reg_to_regnum (gdbarch, rs6000_stab_reg_to_regnum);
   set_gdbarch_dwarf2_reg_to_regnum (gdbarch, rs6000_dwarf2_reg_to_regnum);
-- 
2.37.2

RE: [Patch 1/2] PowerPC, Fix-test-gdb.base-store.exp

[Andrew Burgess]

Carl Love <cel@us.ibm.com> writes:

> Andrew:
>
> Thanks for the review and comments.  See responses below.

Carl,

Sorry for my slow reply.

>
> On Mon, 2023-10-16 at 15:31 +0100, Andrew Burgess wrote:
>> Carl Love <cel@us.ibm.com> writes:
>> 
>> > GDB maintainers:
>> > 
>> > This is the first patch in the series which fixes the DWWARF
>> > register
>> > mapping and signal handling issues on PowerPC.
>> > 
>> >                   Carl
>> > 
>> > -----------------------------------------------
>> > 
>> > rs6000, Fix Linux DWARF register mapping
>> > 
>> > The PowerPC DWARF register mapping is the same for the .eh_frame
>> > and
>> > .debug_frame on Linux.  PowerPC uses different mapping for
>> > .eh_frame and
>> > .debug_frame on other operating systems.  The current GDB support
>> > for
>> > mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum
>> > and
>> > rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct
>> > for Linux.
>> > The files have some legacy mappings for spe_acc, spefscr, EV which
>> > was
>> > removed from GCC in 2017.
>> > 
>> > This patch adds a two new functions
>> > rs6000_linux_dwarf2_reg_to_regnum,
>> > and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c
>> > to handle
>> > the DWARF register mappings on Linux.  Function
>> > rs6000_linux_dwarf2_reg_to_regnum is installed for both
>> > gdb_dwarf_to_regnum
>> > and gdbarch_stab_reg_to_regnum since the mappings are the same.
>> > 
>> > The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is updated
>> > to
>> > call set_gdbarch_dwarf2_reg_to_regnum map the new function
>> > rs6000_linux_dwarf2_reg_to_regnum for the architecture.  Similarly,
>> > dwarf2_frame_set_adjust_regnum is called to map
>> > rs6000_linux_adjust_frame_regnum into the architecture.
>> > 
>> > The second issue fixed by this patch is the check for subroutine
>> > process_event_stop_test.  Need to make sure the frame is not the
>> > SIGTRAMP_FRAME.  The sequence of events on most platforms is:
>> 
>> Usually for GDB we avoid bundling unrelated changes into a single
>> commit.  Each commit should address one self contained issue (as far
>> as
>> possible).
>> 
>> I really struggling to see any connection between the two fixes you
>> have
>> here.
>
> As mentioned in the commit log, the first patch which fixes the DWARF
> register mapping fixes two of the 5 failures seen in store.exp. 
> Specifically the patch fixes the issue of GDB not stopping in the
> handler which results in the step.exp test failing.  The second patch
> then fixes the rest of the issues with the step.exp test.

I'm now even more confused.

The commit message for the first patch suggests that it contains two
separate fixes, but the commit message, even your updated commit message
for 'ver2' only mentions store.exp.

To be more specific, in patch 1/2, the changes in ppc-linux-tdep.c seem
unrelated to the changes in infrun.c.  And I'm confused about how the
changes in infrun.c can fix anything in the store.exp test script -- the
comments relating to that part of the patch specifically talk about
'nexti' and signal handlers, but I don't see either of these being used
in store.exp (we do use 'next' though, so maybe that's what you mean?)
But I'm not clear if a signal is invoked in that test at all.

In the text above you do mention step.exp, so maybe that's what the
infrun.c changes are fixing?  I'll grab a PPC machine and have a play,
but your 'ver 2' commit message has no mention of step.exp, so if that
test is important you might need to update the text.

Usually in GDB when we talk about each patch containing a single fix
we're talking about changes to GDB functionality, not fixing a test
script.  So it's not: 'Patch 1/1 fixes all of store.exp' but rather,
'Patch 1/2 fixes PPC DWARF register mapping' and 'Patch 2/2 fixes nexti
blah blah signal frames'.

>> 
>> >   1) Some code is running when a signal arrives.
>> >   2) The kernel handles the signal and dispatches to the handler.
>> >     ...
>> > 
>> > However on PowerPC the sequence of events is:
>> > 
>> >   1) Some code is running when a signal arrives.
>> >   2) The kernel handles the signal and dispatches to the
>> > trampoline.
>> >   3) The trampoline performs a normal function call to the handler.
>> >       ...
>> > 
>> > We want "nexti" to step into, not over, signal handlers invoked
>> > by the kernel.  This is the case most platforms as the kernel puts
>> > a
>> > signal trampoline frame onto the stack to handle proper return
>> > after the
>> > handler.  However, on some platforms such as PowerPC, the kernel
>> > actually
>> > uses a trampoline to handle *invocation* of the handler.
>> > 
>> > The issue is fixed in function process_event_stop_test by adding a
>> > check
>> > that the frame is not a SIGTRAMP_FRAME to the if statement to stop
>> > in
>> > a subroutine call.  This prevents GDB from erroneously detecting
>> > the
>> > trampoline invocation as a subroutine call.
>> > 
>> > This patch fixes two regression test failures in
>> > gdb.base/store.exp.  It
>> > also fixes two regression failures in gdb.python/py-thread-
>> > exited.exp.
>> 
>> On the one random PPC box I tried this patch on, I'm not seeing any
>> failures in gdb.python/py-thread-exited.exp either before, or after
>> this
>> commit.
>> 
>> Which tests in gdb.python/py-thread-exited.exp are you seeing as
>> broken?
>> And which of the two fixes in this commit fix the problems you're
>> seeing?
>
> The comment about the py-thread-exited.exp should have been removed.  I
> found that sometimes that test fails and sometime passes.  I have yet
> to dig into it and figure out why the test is inconsistent.  The
> inconsistent behavior exists with and without these patches.
>
> I will remove the comment about the gdb.python/py-thread-exited.exp
> fixes as that is erroneous.

Thanks.

>
>
>> 
>> > Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10
>> > with no
>> > new regressions.
>> > ---
>> >  gdb/infrun.c         | 13 ++++++++++
>> >  gdb/ppc-linux-tdep.c | 56
>> > ++++++++++++++++++++++++++++++++++++++++++++
>> >  2 files changed, 69 insertions(+)
>> > 
>> > diff --git a/gdb/infrun.c b/gdb/infrun.c
>> > index 4730d290442..922d8a6913d 100644
>> > --- a/gdb/infrun.c
>> > +++ b/gdb/infrun.c
>> > @@ -7334,8 +7334,21 @@ process_event_stop_test (struct
>> > execution_control_state *ecs)
>> >       initial outermost frame, before sp was valid, would
>> >       have code_addr == &_start.  See the comment in
>> > frame_id::operator==
>> >       for more.  */
>> > +
>> > +  /* We want "nexti" to step into, not over, signal handlers
>> > invoked
>> > +     by the kernel, therefore this subroutine check should not
>> > trigger
>> > +     for a signal handler invocation.  On most platforms, this is
>> > already
>> > +     not the case, as the kernel puts a signal trampoline frame
>> > onto the
>> > +     stack to handle proper return after the handler, and
>> > therefore at this
>> > +     point, the current frame is a grandchild of the step frame,
>> > not a
>> > +     child.  However, on some platforms, the kernel actually uses
>> > a
>> > +     trampoline to handle *invocation* of the handler.  In that
>> > case,
>> > +     when executing the first instruction of the trampoline, this
>> > check
>> > +     would erroneously detect the trampoline invocation as a
>> > subroutine
>> > +     call.  Fix this by checking for SIGTRAMP_FRAME.  */
>> >    if ((get_stack_frame_id (frame)
>> >         != ecs->event_thread->control.step_stack_frame_id)
>> > +      && get_frame_type (frame) != SIGTRAMP_FRAME
>> >        && ((frame_unwind_caller_id (get_current_frame ())
>> >  	   == ecs->event_thread->control.step_stack_frame_id)
>> >  	  && ((ecs->event_thread->control.step_stack_frame_id
>> > diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
>> > index 784dafa59db..7fb90799dff 100644
>> > --- a/gdb/ppc-linux-tdep.c
>> > +++ b/gdb/ppc-linux-tdep.c
>> > @@ -83,6 +83,7 @@
>> >  #include "features/rs6000/powerpc-isa207-vsx64l.c"
>> >  #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
>> >  #include "features/rs6000/powerpc-e500l.c"
>> > +#include "dwarf2/frame.h"
>> >  
>> >  /* Shared library operations for PowerPC-Linux.  */
>> >  static struct target_so_ops powerpc_so_ops;
>> > @@ -2088,6 +2089,52 @@ ppc_linux_displaced_step_prepare  (gdbarch
>> > *arch, thread_info *thread,
>> >    return per_inferior->disp_step_buf->prepare (thread,
>> > displaced_pc);
>> >  }
>> >  
>> > +/* Convert a Dwarf 2 register number to a GDB register number for
>> > Linux.  */
>> > +static int
>> > +rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int
>> > num)
>> > +{
>> > +  ppc_gdbarch_tdep *tdep =
>> > gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
>> > +
>> > +  if (0 <= num && num <= 31)
>> > +    return tdep->ppc_gp0_regnum + num;
>> > +  else if (32 <= num && num <= 63)
>> > +    /* FIXME: jimb/2004-05-05: What should we do when the debug
>> > info
>> > +       specifies registers the architecture doesn't have?  Our
>> > +       callers don't check the value we return.  */
>> 
>> I see this comment was just copied from else where, but isn't the
>> answer
>> just: return -1 ?
>> 
>> The comment about the 'return -1' at the trail of this function seems
>> to
>> suggest that would be the correct thing to do.
>> 
>> I guess I'm asking: do we need to add another copy of this (I think
>> out
>> of date) fixme?
>
> Yes, the function is based on rs6000_dwarf2_reg_to_regnum with the
> specific changes for the Linux DWARF mappings.  The comment looked out
> of date to me, but I left it for consistency with the other two
> functions that have the same comment. It would probably be best to
> investigate the comment further and update it in all places in a
> separate patch. 
>
> Would it be acceptable to leave the comment as is for now, for
> consistency sake, and I will work on a separate cleanup patch to
> address removing the comment in the original two places and this
> additional place?  I will want to look into it a bit more but I think
> we can just remove the comment.  But I do want to verify that the
> return value is never used first.

I took a quick look.  There are three callers: 1 in dwarf2/loc.c, and 2
in jit.c.  One of the callers in jit.c does fail to check the return
value, but this looks like a bug to me.  The other callers do check for
a -1 return value.  The comment in gdbarch-gen.h is also explicit that
the right thing to do is return -1.

Coupled with the fact that the comment, in its current location just
makes no sense I think the best idea would be to drop it from your new
function.  Cleaning up the older code in the future would be nice, but
is not required.  But I don't think we need to introduce more incorrect
comments just for consistency.

Thanks,
Andrew

Re: [PATCH 2/2] PowerPC, Fix-test-gdb.base-store.exp

[Andrew Burgess]

Carl Love <cel@linux.ibm.com> writes:

> GDB maintainers:
>
> Ver 2:  In the new function, rs6000_value_from_register, moved the
> declaration of frame to where it gets initialized.   Patch was retested
> on Power10.
>
> This is the second patch which fixes the 128-bit floating point
> register mappings.  This fixes the remaining three issues with the
> store.exp test.
>
>              Carl 
>
> -----------------------------------------
> rs6000, Fix test gdb.base/store.exp
>
> The test currently fails for IEEE 128-bit floating point types.  PowerPC
> supports the IBM double 128-bit floating point format and IEEE 128-bit
> format.  The IBM double 128-bit floating point format uses two 64-bit
> floating point registers to store the 128-bit value.  The IEEE 128-bit
> floating point format stores the value in a single 128-bit vector-scalar
> register (vsr).
>
> The various floating point values, 32-bit float, 64-bit double, IBM double
> 128-bit float and IEEE 128-bit floating point numbers are all mapped to the
> DWARF fpr numbers.  The issue is the IEEE 128-bit floating point values are
> actually stored in a vsr not the fprs.  This patch changes the register
> mapping for the vsrs from the fpr to the vsr registers so the value is
> properly accessed by GDB.  The functions rs6000_linux_register_to_value,
> rs6000_linux_value_to_register, rs6000_linux_value_from_register check if
> the value is an IEEE 128-bit floating point value and adjust the register
> number as needed.  The test in function rs6000_convert_register_p is fixed
> so it is only true for floating point values.
>
> This patch fixes three regression tests in gdb.base/store.exp.

If this doesn't depend on patch #1 then feel free to go ahead an merge.

Approved-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew


>
> The patch has been tested on Power 8 LE/BE, Power 9 LE/BE and Power 10 LE
> with no regressions.
> ---
>  gdb/ppc-linux-tdep.c |  4 +++
>  gdb/rs6000-tdep.c    | 65 +++++++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 68 insertions(+), 1 deletion(-)
>
> diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> index dc03430e2af..fac56d961cb 100644
> --- a/gdb/ppc-linux-tdep.c
> +++ b/gdb/ppc-linux-tdep.c
> @@ -63,6 +63,7 @@
>  #include <ctype.h>
>  #include "elf-bfd.h"
>  #include "producer.h"
> +#include "target-float.h"
>  
>  #include "features/rs6000/powerpc-32l.c"
>  #include "features/rs6000/powerpc-altivec32l.c"
> @@ -2102,6 +2103,9 @@ rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
>      /* FIXME: jimb/2004-05-05: What should we do when the debug info
>         specifies registers the architecture doesn't have?  Our
>         callers don't check the value we return.  */
> +    /* Map dwarf register numbers for floating point, double, IBM double and
> +       IEEE 128-bit floating point to the fpr range.  Will have to fix the
> +       mapping for the IEEE 128-bit register numbers later.  */
>      return tdep->ppc_fp0_regnum + (num - 32);
>    else if (77 <= num && num < 77 + 32)
>      return tdep->ppc_vr0_regnum + (num - 77);
> diff --git a/gdb/rs6000-tdep.c b/gdb/rs6000-tdep.c
> index 23397d037ae..186646673f0 100644
> --- a/gdb/rs6000-tdep.c
> +++ b/gdb/rs6000-tdep.c
> @@ -2676,7 +2676,25 @@ rs6000_convert_register_p (struct gdbarch *gdbarch, int regnum,
>  	  && regnum < tdep->ppc_fp0_regnum + ppc_num_fprs
>  	  && type->code () == TYPE_CODE_FLT
>  	  && (type->length ()
> -	      != builtin_type (gdbarch)->builtin_double->length ()));
> +	      == builtin_type (gdbarch)->builtin_float->length ()));
> +}
> +
> +static int
> +ieee_128_float_regnum_adjust (struct gdbarch *gdbarch, struct type *type,
> +			      int regnum)
> +{
> +  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep> (gdbarch);
> +
> +  /* If we have the an IEEE 128-bit floating point value, need to map the
> +   register number to the corresponding VSR.  */
> +  if (tdep->ppc_vsr0_regnum != -1
> +      && regnum >= tdep->ppc_fp0_regnum
> +      && regnum < (tdep->ppc_fp0_regnum + ppc_num_fprs)
> +      && (gdbarch_long_double_format (gdbarch) == floatformats_ieee_quad)
> +      && (type->length() == 16))
> +    regnum = regnum - tdep->ppc_fp0_regnum + tdep->ppc_vsr0_regnum;
> +
> +  return regnum;
>  }
>  
>  static int
> @@ -2691,6 +2709,10 @@ rs6000_register_to_value (frame_info_ptr frame,
>    
>    gdb_assert (type->code () == TYPE_CODE_FLT);
>  
> +  /* We have an IEEE 128-bit float -- need to change regnum mapping from
> +     fpr to vsr.  */
> +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> +
>    if (!get_frame_register_bytes (frame, regnum, 0,
>  				 gdb::make_array_view (from,
>  						       register_size (gdbarch,
> @@ -2715,11 +2737,51 @@ rs6000_value_to_register (frame_info_ptr frame,
>  
>    gdb_assert (type->code () == TYPE_CODE_FLT);
>  
> +  /* We have an IEEE 128-bit float -- need to change regnum mapping from
> +     fpr to vsr.  */
> +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> +
>    target_float_convert (from, type,
>  			to, builtin_type (gdbarch)->builtin_double);
>    put_frame_register (frame, regnum, to);
>  }
>  
> +static struct value *
> +rs6000_value_from_register (struct gdbarch *gdbarch, struct type *type,
> +			    int regnum, struct frame_id frame_id)
> +{
> +  int len = type->length ();
> +  struct value *value = value::allocate (type);
> +
> +  /* We have an IEEE 128-bit float -- need to change regnum mapping from
> +     fpr to vsr.  */
> +  regnum = ieee_128_float_regnum_adjust (gdbarch, type, regnum);
> +
> +  value->set_lval (lval_register);
> +  frame_info_ptr frame = frame_find_by_id (frame_id);
> +
> +  if (frame == NULL)
> +    frame_id = null_frame_id;
> +  else
> +    frame_id = get_frame_id (get_next_frame_sentinel_okay (frame));
> +
> +  VALUE_NEXT_FRAME_ID (value) = frame_id;
> +  VALUE_REGNUM (value) = regnum;
> +
> +  /* Any structure stored in more than one register will always be
> +     an integral number of registers.  Otherwise, you need to do
> +     some fiddling with the last register copied here for little
> +     endian machines.  */
> +  if (type_byte_order (type) == BFD_ENDIAN_BIG
> +      && len < register_size (gdbarch, regnum))
> +    /* Big-endian, and we want less than full size.  */
> +    value->set_offset (register_size (gdbarch, regnum) - len);
> +  else
> +    value->set_offset (0);
> +
> +  return value;
> +}
> +
>   /* The type of a function that moves the value of REG between CACHE
>      or BUF --- in either direction.  */
>  typedef enum register_status (*move_ev_register_func) (struct regcache *,
> @@ -8337,6 +8399,7 @@ rs6000_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>    set_gdbarch_convert_register_p (gdbarch, rs6000_convert_register_p);
>    set_gdbarch_register_to_value (gdbarch, rs6000_register_to_value);
>    set_gdbarch_value_to_register (gdbarch, rs6000_value_to_register);
> +  set_gdbarch_value_from_register (gdbarch, rs6000_value_from_register);
>  
>    set_gdbarch_stab_reg_to_regnum (gdbarch, rs6000_stab_reg_to_regnum);
>    set_gdbarch_dwarf2_reg_to_regnum (gdbarch, rs6000_dwarf2_reg_to_regnum);
> -- 
> 2.37.2

Re: [PATCH 1/2, ver2] PowerPC, Fix-test-gdb.base-store.exp

[Andrew Burgess]

Carl Love <cel@linux.ibm.com> writes:

> GDB maintainers:
>
> Ver2, added a missing blank line, removed an extra blank line, fixed
> spelling mistakes.  Removed comment in ChangeLog about fixing py-
> thread-exited.exp test errors.  Patch just fixes issues with the
> store.exp.  Did not change the comment:
>
>> +    /* FIXME: jimb/2004-05-05: What should we do when the debug info
>> +       specifies registers the architecture doesn't have?  Our
>> +       callers don't check the value we return.  */
>   
> Will create a new patch to address the comment in all three places in
> the source code.
>
> Note, fixing the register mapping fixes two of the five test failures
> for the store.exp test.
>
> Patch was retested on Power10.
>
> This is the first patch in the series which fixes the DWWARF register
> mapping and signal handling issues on PowerPC.
>
>                   Carl
>
>
> -------------------------------------------------
> Fix Linux DWARF register mapping
>
> The PowerPC DWARF register mapping is the same for the .eh_frame and
> .debug_frame on Linux.  PowerPC uses different mapping for .eh_frame and
> .debug_frame on other operating systems.  The current GDB support for
> mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum and
> rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct for Linux.
> The files have some legacy mappings for spe_acc, spefscr, EV which was
> removed from GCC in 2017.
>
> This patch adds a two new functions rs6000_linux_dwarf2_reg_to_regnum,
> and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c to handle
> the DWARF register mappings on Linux.  Function
> rs6000_linux_dwarf2_reg_to_regnum is installed for both gdb_dwarf_to_regnum
> and gdbarch_stab_reg_to_regnum since the mappings are the same.
>
> The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is updated to
> call set_gdbarch_dwarf2_reg_to_regnum map the new function
> rs6000_linux_dwarf2_reg_to_regnum for the architecture.  Similarly,
> dwarf2_frame_set_adjust_regnum is called to map
> rs6000_linux_adjust_frame_regnum into the architecture.
>
> The second issue fixed by this patch is the check for subroutine
> process_event_stop_test.  Need to make sure the frame is not the
> SIGTRAMP_FRAME.  The sequence of events on most platforms is:
>
>   1) Some code is running when a signal arrives.
>   2) The kernel handles the signal and dispatches to the handler.
>     ...
>
> However on PowerPC the sequence of events is:
>
>   1) Some code is running when a signal arrives.
>   2) The kernel handles the signal and dispatches to the trampoline.
>   3) The trampoline performs a normal function call to the handler.
>       ...
>
> We want "nexti" to step into, not over, signal handlers invoked
> by the kernel.  This is the case most platforms as the kernel puts a
> signal trampoline frame onto the stack to handle proper return after the
> handler.  However, on some platforms such as PowerPC, the kernel actually
> uses a trampoline to handle *invocation* of the handler.
>
> The issue is fixed in function process_event_stop_test by adding a check
> that the frame is not a SIGTRAMP_FRAME to the if statement to stop in
> a subroutine call.  This prevents GDB from erroneously detecting the
> trampoline invocation as a subroutine call.
>
> This patch fixes two regression test failures in gdb.base/store.exp.
>
> Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10 with no
> new regressions.

Hi Carl,

Sorry for being such a pain w.r.t. this patch.  Honestly, it's mostly
because you touched infrun.c that I'm so interested here.

I left some notes here that need addressing:

  https://inbox.sourceware.org/gdb-patches/6f9c8fa20962129048384d74f6f15d1b37d255ed.camel@us.ibm.com/T/#m83b4f0d7da45f15c2df44344fbf3e326cf7435e3

But I wonder if you could be more specific about when you would expect
to see the failures in gdb.base/store.exp.  I grabbed a random Power9
Linux machine and tried running store.exp with an unpatched GDB, and see
no failures.  I guess there's a specific architecture/compiler combo
that I need in order to see failures -- but if those details are in the
above text, I'm just not seeing them.

Could you give some more details about the setup needed to see failures
on store.exp.

And I'd like to see clearer details about which tests the infrun.c
changes will fix.

Thanks,
Andrew




> ---
>  gdb/infrun.c         | 13 ++++++++++
>  gdb/ppc-linux-tdep.c | 56 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 69 insertions(+)
>
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 4730d290442..922d8a6913d 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -7334,8 +7334,21 @@ process_event_stop_test (struct execution_control_state *ecs)
>       initial outermost frame, before sp was valid, would
>       have code_addr == &_start.  See the comment in frame_id::operator==
>       for more.  */
> +
> +  /* We want "nexti" to step into, not over, signal handlers invoked
> +     by the kernel, therefore this subroutine check should not trigger
> +     for a signal handler invocation.  On most platforms, this is already
> +     not the case, as the kernel puts a signal trampoline frame onto the
> +     stack to handle proper return after the handler, and therefore at this
> +     point, the current frame is a grandchild of the step frame, not a
> +     child.  However, on some platforms, the kernel actually uses a
> +     trampoline to handle *invocation* of the handler.  In that case,
> +     when executing the first instruction of the trampoline, this check
> +     would erroneously detect the trampoline invocation as a subroutine
> +     call.  Fix this by checking for SIGTRAMP_FRAME.  */
>    if ((get_stack_frame_id (frame)
>         != ecs->event_thread->control.step_stack_frame_id)
> +      && get_frame_type (frame) != SIGTRAMP_FRAME
>        && ((frame_unwind_caller_id (get_current_frame ())
>  	   == ecs->event_thread->control.step_stack_frame_id)
>  	  && ((ecs->event_thread->control.step_stack_frame_id
> diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> index 784dafa59db..dc03430e2af 100644
> --- a/gdb/ppc-linux-tdep.c
> +++ b/gdb/ppc-linux-tdep.c
> @@ -83,6 +83,7 @@
>  #include "features/rs6000/powerpc-isa207-vsx64l.c"
>  #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
>  #include "features/rs6000/powerpc-e500l.c"
> +#include "dwarf2/frame.h"
>  
>  /* Shared library operations for PowerPC-Linux.  */
>  static struct target_so_ops powerpc_so_ops;
> @@ -2088,6 +2089,52 @@ ppc_linux_displaced_step_prepare  (gdbarch *arch, thread_info *thread,
>    return per_inferior->disp_step_buf->prepare (thread, displaced_pc);
>  }
>  
> +/* Convert a Dwarf 2 register number to a GDB register number for Linux.  */
> +
> +static int
> +rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
> +{
> +  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
> +
> +  if (0 <= num && num <= 31)
> +    return tdep->ppc_gp0_regnum + num;
> +  else if (32 <= num && num <= 63)
> +    /* FIXME: jimb/2004-05-05: What should we do when the debug info
> +       specifies registers the architecture doesn't have?  Our
> +       callers don't check the value we return.  */
> +    return tdep->ppc_fp0_regnum + (num - 32);
> +  else if (77 <= num && num < 77 + 32)
> +    return tdep->ppc_vr0_regnum + (num - 77);
> +  else
> +    switch (num)
> +      {
> +      case 65:
> +	return tdep->ppc_lr_regnum;
> +      case 66:
> +	return tdep->ppc_ctr_regnum;
> +      case 76:
> +	return tdep->ppc_xer_regnum;
> +      case 109:
> +	return tdep->ppc_vrsave_regnum;
> +      case 110:
> +	return tdep->ppc_vrsave_regnum - 1; /* vscr */
> +      }
> +
> +  /* Unknown DWARF register number.  */
> +  return -1;
> +}
> +
> +/* Translate a .eh_frame register to DWARF register, or adjust a
> +   .debug_frame register.  */
> +
> +static int
> +rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
> +				  int eh_frame_p)
> +{
> +  /* Linux uses the same numbering for .debug_frame numbering as .eh_frame.  */
> +  return num;
> +}
> +
>  static void
>  ppc_linux_init_abi (struct gdbarch_info info,
>  		    struct gdbarch *gdbarch)
> @@ -2135,6 +2182,15 @@ ppc_linux_init_abi (struct gdbarch_info info,
>    set_gdbarch_stap_is_single_operand (gdbarch, ppc_stap_is_single_operand);
>    set_gdbarch_stap_parse_special_token (gdbarch,
>  					ppc_stap_parse_special_token);
> +  /* Linux DWARF register mapping is different from the other OSes.  */
> +  set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  /* Note on Linux the mapping for the DWARF registers and the stab registers
> +     use the same numbers.  Install rs6000_linux_dwarf2_reg_to_regnum for the
> +     stab register mappings as well.  */
> +  set_gdbarch_stab_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  dwarf2_frame_set_adjust_regnum (gdbarch, rs6000_linux_adjust_frame_regnum);
>  
>    if (tdep->wordsize == 4)
>      {
> -- 
> 2.37.2

Re: [Patch 1/2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

Andrew:

On Tue, 2023-10-24 at 09:50 +0100, Andrew Burgess wrote:
> Carl Love <cel@us.ibm.com> writes:
> 
> > Andrew:
> > 
> > Thanks for the review and comments.  See responses below.
> 
> Carl,
> 
> Sorry for my slow reply.
> 
> > On Mon, 2023-10-16 at 15:31 +0100, Andrew Burgess wrote:
> > > Carl Love <cel@us.ibm.com> writes:
> > > 
> > > > GDB maintainers:
> > > > 
> > > > This is the first patch in the series which fixes the DWWARF
> > > > register
> > > > mapping and signal handling issues on PowerPC.
> > > > 
> > > >                   Carl
> > > > 
> > > > -----------------------------------------------
> > > > 
> > > > rs6000, Fix Linux DWARF register mapping
> > > > 
> > > > The PowerPC DWARF register mapping is the same for the
> > > > .eh_frame
> > > > and
> > > > .debug_frame on Linux.  PowerPC uses different mapping for
> > > > .eh_frame and
> > > > .debug_frame on other operating systems.  The current GDB
> > > > support
> > > > for
> > > > mapping the DWARF registers in
> > > > rs6000_linux_dwarf2_reg_to_regnum
> > > > and
> > > > rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not
> > > > correct
> > > > for Linux.
> > > > The files have some legacy mappings for spe_acc, spefscr, EV
> > > > which
> > > > was
> > > > removed from GCC in 2017.
> > > > 
> > > > This patch adds a two new functions
> > > > rs6000_linux_dwarf2_reg_to_regnum,
> > > > and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-
> > > > tdep.c
> > > > to handle
> > > > the DWARF register mappings on Linux.  Function
> > > > rs6000_linux_dwarf2_reg_to_regnum is installed for both
> > > > gdb_dwarf_to_regnum
> > > > and gdbarch_stab_reg_to_regnum since the mappings are the same.
> > > > 
> > > > The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is
> > > > updated
> > > > to
> > > > call set_gdbarch_dwarf2_reg_to_regnum map the new function
> > > > rs6000_linux_dwarf2_reg_to_regnum for the
> > > > architecture.  Similarly,
> > > > dwarf2_frame_set_adjust_regnum is called to map
> > > > rs6000_linux_adjust_frame_regnum into the architecture.
> > > > 
> > > > The second issue fixed by this patch is the check for
> > > > subroutine
> > > > process_event_stop_test.  Need to make sure the frame is not
> > > > the
> > > > SIGTRAMP_FRAME.  The sequence of events on most platforms is:
> > > 
> > > Usually for GDB we avoid bundling unrelated changes into a single
> > > commit.  Each commit should address one self contained issue (as
> > > far
> > > as
> > > possible).
> > > 
> > > I really struggling to see any connection between the two fixes
> > > you
> > > have
> > > here.
> > 
> > As mentioned in the commit log, the first patch which fixes the
> > DWARF
> > register mapping fixes two of the 5 failures seen in store.exp. 
> > Specifically the patch fixes the issue of GDB not stopping in the
> > handler which results in the step.exp test failing.  The second
> > patch
> > then fixes the rest of the issues with the step.exp test.
> 
> I'm now even more confused.
> 
> The commit message for the first patch suggests that it contains two
> separate fixes, but the commit message, even your updated commit
> message
> for 'ver2' only mentions store.exp.
> 
> To be more specific, in patch 1/2, the changes in ppc-linux-tdep.c
> seem
> unrelated to the changes in infrun.c.  And I'm confused about how the
> changes in infrun.c can fix anything in the store.exp test script --
> the
> comments relating to that part of the patch specifically talk about
> 'nexti' and signal handlers, but I don't see either of these being
> used
> in store.exp (we do use 'next' though, so maybe that's what you
> mean?)
> But I'm not clear if a signal is invoked in that test at all.
> 
> In the text above you do mention step.exp, so maybe that's what the
> infrun.c changes are fixing?  I'll grab a PPC machine and have a
> play,
> but your 'ver 2' commit message has no mention of step.exp, so if
> that
> test is important you might need to update the text.
> 

The 128-bit floating point issues in store.exp will need a Power10
system which supports the 128-bit floating point types.  A Power 9
system is not sufficient.  

OK, I think I see what is missing in the explanation. So initially, I
fixed the DWARF register mapping for the store.exp test.  This fixed a
couple of the issues with the store.exp test.  Then in the second patch
we fixed the DWARF register mapping for the 128-bit floating point
values.  Specifically, DWARF used the same register numbers for 64-bit
and 128-bit floating point values.  However, the 128-bit floating point
values are stored in the VSR register file while the 64-bit values are
stored in the floating point registers.  The function
ieee_128_float_regnum_adjust takes care of that fix.  So at this point,
the store.exp test works.  

But now I have a regression failure on gdb.base/sigstep.exp.  This test
is specifically dealing with signal handlers.  Fixing the register
mapping, in patch 1, exposed an underlying bug in the signal handler
code.  The fixes for the nexti, stepi in the signal handling fixes the
regression error.  The signal handling fix is needed as part of the
DWARF register mapping fix so we don't have any regression failures and
so these fixes got rolled into the first patch but it was not really
explained in the original patch description.  So yes, there are really
two things getting fixed in the first patch. But you don't see the
signal handler issue until after the register mapping is fixed for
Linux.

The signal handler issues should be exposed on Power 9 if we split out
the DWARF register mapping from the signal handler fixes.  I didn't
play with these individually on Power 9 as part of the patch work.  All
of the patch work was done on Power 10.

So maybe it will be best if I redo the two patch sequence into three
patches.  Patch 1, fix the mapping; Patch 2 fix the signal handling
issue exposed once the register mapping is fixed; Patch 3 fix the
handling of the 128-bit float DWARF register mapping.  This should then
make it clearer what is going on in each patch.  Thoughts?

                      Carl 

> Usually in GDB when we talk about each patch containing a single fix
> we're talking about changes to GDB functionality, not fixing a test
> script.  So it's not: 'Patch 1/1 fixes all of store.exp' but rather,
> 'Patch 1/2 fixes PPC DWARF register mapping' and 'Patch 2/2 fixes
> nexti
> blah blah signal frames'.
> 
> > > >   1) Some code is running when a signal arrives.
> > > >   2) The kernel handles the signal and dispatches to the
> > > > handler.
> > > >     ...
> > > > 
> > > > However on PowerPC the sequence of events is:
> > > > 
> > > >   1) Some code is running when a signal arrives.
> > > >   2) The kernel handles the signal and dispatches to the
> > > > trampoline.
> > > >   3) The trampoline performs a normal function call to the
> > > > handler.
> > > >       ...
> > > > 
> > > > We want "nexti" to step into, not over, signal handlers invoked
> > > > by the kernel.  This is the case most platforms as the kernel
> > > > puts
> > > > a
> > > > signal trampoline frame onto the stack to handle proper return
> > > > after the
> > > > handler.  However, on some platforms such as PowerPC, the
> > > > kernel
> > > > actually
> > > > uses a trampoline to handle *invocation* of the handler.
> > > > 
> > > > The issue is fixed in function process_event_stop_test by
> > > > adding a
> > > > check
> > > > that the frame is not a SIGTRAMP_FRAME to the if statement to
> > > > stop
> > > > in
> > > > a subroutine call.  This prevents GDB from erroneously
> > > > detecting
> > > > the
> > > > trampoline invocation as a subroutine call.
> > > > 
> > > > This patch fixes two regression test failures in
> > > > gdb.base/store.exp.  It
> > > > also fixes two regression failures in gdb.python/py-thread-
> > > > exited.exp.
> > > 
> > > On the one random PPC box I tried this patch on, I'm not seeing
> > > any
> > > failures in gdb.python/py-thread-exited.exp either before, or
> > > after
> > > this
> > > commit.
> > > 
> > > Which tests in gdb.python/py-thread-exited.exp are you seeing as
> > > broken?
> > > And which of the two fixes in this commit fix the problems you're
> > > seeing?
> > 
> > The comment about the py-thread-exited.exp should have been
> > removed.  I
> > found that sometimes that test fails and sometime passes.  I have
> > yet
> > to dig into it and figure out why the test is inconsistent.  The
> > inconsistent behavior exists with and without these patches.
> > 
> > I will remove the comment about the gdb.python/py-thread-exited.exp
> > fixes as that is erroneous.
> 
> Thanks.
> 
> > 
> > > > Patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10
> > > > with no
> > > > new regressions.
> > > > ---
> > > >  gdb/infrun.c         | 13 ++++++++++
> > > >  gdb/ppc-linux-tdep.c | 56
> > > > ++++++++++++++++++++++++++++++++++++++++++++
> > > >  2 files changed, 69 insertions(+)
> > > > 
> > > > diff --git a/gdb/infrun.c b/gdb/infrun.c
> > > > index 4730d290442..922d8a6913d 100644
> > > > --- a/gdb/infrun.c
> > > > +++ b/gdb/infrun.c
> > > > @@ -7334,8 +7334,21 @@ process_event_stop_test (struct
> > > > execution_control_state *ecs)
> > > >       initial outermost frame, before sp was valid, would
> > > >       have code_addr == &_start.  See the comment in
> > > > frame_id::operator==
> > > >       for more.  */
> > > > +
> > > > +  /* We want "nexti" to step into, not over, signal handlers
> > > > invoked
> > > > +     by the kernel, therefore this subroutine check should not
> > > > trigger
> > > > +     for a signal handler invocation.  On most platforms, this
> > > > is
> > > > already
> > > > +     not the case, as the kernel puts a signal trampoline
> > > > frame
> > > > onto the
> > > > +     stack to handle proper return after the handler, and
> > > > therefore at this
> > > > +     point, the current frame is a grandchild of the step
> > > > frame,
> > > > not a
> > > > +     child.  However, on some platforms, the kernel actually
> > > > uses
> > > > a
> > > > +     trampoline to handle *invocation* of the handler.  In
> > > > that
> > > > case,
> > > > +     when executing the first instruction of the trampoline,
> > > > this
> > > > check
> > > > +     would erroneously detect the trampoline invocation as a
> > > > subroutine
> > > > +     call.  Fix this by checking for SIGTRAMP_FRAME.  */
> > > >    if ((get_stack_frame_id (frame)
> > > >         != ecs->event_thread->control.step_stack_frame_id)
> > > > +      && get_frame_type (frame) != SIGTRAMP_FRAME
> > > >        && ((frame_unwind_caller_id (get_current_frame ())
> > > >  	   == ecs->event_thread->control.step_stack_frame_id)
> > > >  	  && ((ecs->event_thread->control.step_stack_frame_id
> > > > diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> > > > index 784dafa59db..7fb90799dff 100644
> > > > --- a/gdb/ppc-linux-tdep.c
> > > > +++ b/gdb/ppc-linux-tdep.c
> > > > @@ -83,6 +83,7 @@
> > > >  #include "features/rs6000/powerpc-isa207-vsx64l.c"
> > > >  #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
> > > >  #include "features/rs6000/powerpc-e500l.c"
> > > > +#include "dwarf2/frame.h"
> > > >  
> > > >  /* Shared library operations for PowerPC-Linux.  */
> > > >  static struct target_so_ops powerpc_so_ops;
> > > > @@ -2088,6 +2089,52 @@
> > > > ppc_linux_displaced_step_prepare  (gdbarch
> > > > *arch, thread_info *thread,
> > > >    return per_inferior->disp_step_buf->prepare (thread,
> > > > displaced_pc);
> > > >  }
> > > >  
> > > > +/* Convert a Dwarf 2 register number to a GDB register number
> > > > for
> > > > Linux.  */
> > > > +static int
> > > > +rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch,
> > > > int
> > > > num)
> > > > +{
> > > > +  ppc_gdbarch_tdep *tdep =
> > > > gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
> > > > +
> > > > +  if (0 <= num && num <= 31)
> > > > +    return tdep->ppc_gp0_regnum + num;
> > > > +  else if (32 <= num && num <= 63)
> > > > +    /* FIXME: jimb/2004-05-05: What should we do when the
> > > > debug
> > > > info
> > > > +       specifies registers the architecture doesn't have?  Our
> > > > +       callers don't check the value we return.  */
> > > 
> > > I see this comment was just copied from else where, but isn't the
> > > answer
> > > just: return -1 ?
> > > 
> > > The comment about the 'return -1' at the trail of this function
> > > seems
> > > to
> > > suggest that would be the correct thing to do.
> > > 
> > > I guess I'm asking: do we need to add another copy of this (I
> > > think
> > > out
> > > of date) fixme?
> > 
> > Yes, the function is based on rs6000_dwarf2_reg_to_regnum with the
> > specific changes for the Linux DWARF mappings.  The comment looked
> > out
> > of date to me, but I left it for consistency with the other two
> > functions that have the same comment. It would probably be best to
> > investigate the comment further and update it in all places in a
> > separate patch. 
> > 
> > Would it be acceptable to leave the comment as is for now, for
> > consistency sake, and I will work on a separate cleanup patch to
> > address removing the comment in the original two places and this
> > additional place?  I will want to look into it a bit more but I
> > think
> > we can just remove the comment.  But I do want to verify that the
> > return value is never used first.
> 
> I took a quick look.  There are three callers: 1 in dwarf2/loc.c, and
> 2
> in jit.c.  One of the callers in jit.c does fail to check the return
> value, but this looks like a bug to me.  The other callers do check
> for
> a -1 return value.  The comment in gdbarch-gen.h is also explicit
> that
> the right thing to do is return -1.
> 
> Coupled with the fact that the comment, in its current location just
> makes no sense I think the best idea would be to drop it from your
> new
> function.  Cleaning up the older code in the future would be nice,
> but
> is not required.  But I don't think we need to introduce more
> incorrect
> comments just for consistency.
> 
> Thanks,
> Andrew
> 

RE: [PATCH 1/2, ver2] PowerPC, Fix-test-gdb.base-store.exp

[Ulrich Weigand]

Andrew Burgess <aburgess@redhat.com> wrote:

>Sorry for being such a pain w.r.t. this patch.  Honestly, it's mostly
>because you touched infrun.c that I'm so interested here.
[...]
>And I'd like to see clearer details about which tests the infrun.c
>changes will fix.

Hi Andrew, as I suggested that particular infrun.c change
to Carl, let me add some background to what Carl replied.

This one-line change in infrun.c fixes a (potential) common-code
bug in existing code.  However, this bug is likely dormant on
all current platforms:

First of all, the bug only shows up on platforms where the
kernel uses a trampoline to dispatch *calls to* the signal
handler (not just *returns from* the signal handler).  Many
platforms use a trampoline for signal return, and that is
working fine, but the only platform I'm aware of that uses
a trampoline for signal handler calls is (recent kernels for)
PowerPC.  I believe the rationale for using a trampoline here
is to improve performance by avoiding unbalancing of the
branch predictor's call/return stack.

However, on PowerPC the bug is dormant as well as it is hidden
by *another* bug that prevents correct unwinding out of the
signal trampoline.  This is because the custom CFI for the
trampoline uses a register number (VSCR) that is not ever used
by compiler-generated CFI, and that particular register is
mapped to an invalid number by the current PowerPC DWARF
mapper.

Now, as Carl fixed the PowerPC DWARF mapper to fix some test
case regressions that showed up on POWER10, he added correct
mappings for all registers including VSCR.  This then caused
unwinding out of the signal trampoline to start working
correctly, which in turn exposed the pre-existing infrun.c bug
in handling signal call trampolines.

Now, that particular bug is that if the kernel uses a signal
call trampoline, infrun.c will see that the current PC is
in a frame that is an immediate child of the step frame (as
the trampoline frame unwinds to the step frame) - and then
incorrectly thinks that a *subroutine call* must have happened.
But we don't want to treat a signal handler invocation like
a subroutine call, in particular we want "nexti" to step
into it.  That's fixed by the one-line change.


Bye,
Ulrich

RE: [PATCH 1/2, ver2] PowerPC, Fix-test-gdb.base-store.exp

[Andrew Burgess]

Ulrich Weigand <Ulrich.Weigand@de.ibm.com> writes:

> Andrew Burgess <aburgess@redhat.com> wrote:
>
>>Sorry for being such a pain w.r.t. this patch.  Honestly, it's mostly
>>because you touched infrun.c that I'm so interested here.
> [...]
>>And I'd like to see clearer details about which tests the infrun.c
>>changes will fix.
>
> Hi Andrew, as I suggested that particular infrun.c change
> to Carl, let me add some background to what Carl replied.
>
> This one-line change in infrun.c fixes a (potential) common-code
> bug in existing code.  However, this bug is likely dormant on
> all current platforms:
>
> First of all, the bug only shows up on platforms where the
> kernel uses a trampoline to dispatch *calls to* the signal
> handler (not just *returns from* the signal handler).  Many
> platforms use a trampoline for signal return, and that is
> working fine, but the only platform I'm aware of that uses
> a trampoline for signal handler calls is (recent kernels for)
> PowerPC.  I believe the rationale for using a trampoline here
> is to improve performance by avoiding unbalancing of the
> branch predictor's call/return stack.
>
> However, on PowerPC the bug is dormant as well as it is hidden
> by *another* bug that prevents correct unwinding out of the
> signal trampoline.  This is because the custom CFI for the
> trampoline uses a register number (VSCR) that is not ever used
> by compiler-generated CFI, and that particular register is
> mapped to an invalid number by the current PowerPC DWARF
> mapper.

Ulrich,

Thanks for the great explanation.

I think adding this to the commit message would be a great improvement.
But also, you said:

> Now, as Carl fixed the PowerPC DWARF mapper to fix some test
> case regressions that showed up on POWER10, he added correct
> mappings for all registers including VSCR.  This then caused
> unwinding out of the signal trampoline to start working
> correctly, which in turn exposed the pre-existing infrun.c bug
> in handling signal call trampolines.

As part of the commit message at this point I'd like to see the name of
at least one (if the number is small, I'd list them all though) test(s)
that required this change in order to keep working correctly.

Often, when I end up looking at old commits in the history, I want to
know, what is an example of something that this change actually fixes,
and it's super frustrating when I have to try and figure this
information out for myself -- given that it must have been known at
commit time.

>
> Now, that particular bug is that if the kernel uses a signal
> call trampoline, infrun.c will see that the current PC is
> in a frame that is an immediate child of the step frame (as
> the trampoline frame unwinds to the step frame) - and then
> incorrectly thinks that a *subroutine call* must have happened.
> But we don't want to treat a signal handler invocation like
> a subroutine call, in particular we want "nexti" to step
> into it.  That's fixed by the one-line change.

Thanks,
Andrew

Re: [PATCH 1/2, ver2] PowerPC, Fix-test-gdb.base-store.exp

[Ulrich Weigand]

Andrew Burgess <aburgess@redhat.com> wrote:

>I think adding this to the commit message would be a great improvement.
>But also, you said:
>
> >Now, as Carl fixed the PowerPC DWARF mapper to fix some test
> >case regressions that showed up on POWER10, he added correct
> >mappings for all registers including VSCR.  This then caused
> >unwinding out of the signal trampoline to start working
> >correctly, which in turn exposed the pre-existing infrun.c bug
> >in handling signal call trampolines.
>
>As part of the commit message at this point I'd like to see the name of
>at least one (if the number is small, I'd list them all though) test(s)
>that required this change in order to keep working correctly.

I believe this showed up in sigstep.exp, but Carl would know for sure.
Carl, please update the commit message as requested by Andrew.

Thanks,
Ulrich

Re: [PATCH 1/2, ver2] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

Ulrich, Andrew:

On Mon, 2023-10-30 at 16:44 +0000, Ulrich Weigand wrote:
> Andrew Burgess <aburgess@redhat.com> wrote:
> 
> > I think adding this to the commit message would be a great
> > improvement.
> > But also, you said:
> > 
> > > Now, as Carl fixed the PowerPC DWARF mapper to fix some test
> > > case regressions that showed up on POWER10, he added correct
> > > mappings for all registers including VSCR.  This then caused
> > > unwinding out of the signal trampoline to start working
> > > correctly, which in turn exposed the pre-existing infrun.c bug
> > > in handling signal call trampolines.
> > 
> > As part of the commit message at this point I'd like to see the
> > name of
> > at least one (if the number is small, I'd list them all though)
> > test(s)
> > that required this change in order to keep working correctly.
> 
> I believe this showed up in sigstep.exp, but Carl would know for
> sure.
> Carl, please update the commit message as requested by Andrew.

I have updated the commit message adding some of the additional detail
that Ulrch gave on the underlying issue.  The commit message now starts
with an overview of the initial issue to be fixed in store.exp followed
by a discussion of the underlying bug that was then exposed by test
sigstep.exp.  The commit message then goes on with the detailed
discussion of the fix for both issues.  Finally, it summarizes the
failures in both store.exp and sigstep.exp that are fixed.  Hopefully
this updated commit message clearly explains the two separate issues
that the patch addresses. 

Thanks for the feedback from Andrew and the help from Ulrich to improve
the commit message. I will post the update patch for your review.

                            Carl 

                              

[PATCH 1/2, ver3] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

Andrew, Ulrich:

Per the discussions, the commit message has been updated to make it
clear that the patch fixes the DWARF register mapping which fixes two
of the test failures in step.exp.  The fix exposed a dormant issue with
the signal handling on PowerPC.  The underlying issue which is then
exposed causes the signal handling test sigstep.exp to fail.  The test
sigstep.exp tests stepping into a signal handler.  The patch also fixes
the underlying signal handler issue.  

This new verion of the patch only updates the commit log to make it
clear the patch is fixing multiple issues.

Please let me know if the commit description is clear and acceptable.

Thanks.

                            Carl 
------------------------------------------------------------
rs6000, Fix Linux DWARF register mapping

Overview of issues fixed by the patch.

The primary issue this patch fixes is the DWARF register mapping for
Linux.  The changes in ppc-linux-tdep.c fix the DWARF register mapping
issues.  The register mapping issue is responsible for two of the
five regression bugs seen in gdb.base/store.exp.

Once the register mapping is fixed, an underlying issue with the unwinding
of the signal trampoline in common-code in ifrun.c was found.  This
underlying bug is best described by Ulrich in the following description.

  The unwinder bug shows up on platforms where the kernel uses a trampoline
  to dispatch "calls to" the signal handler (not just *returns from* the
  signal handler).  Many platforms use a trampoline for signal return, and
  that is working fine, but the only platform I'm (Ulrich) aware of that
  uses a trampoline for signal handler calls is (recent kernels for)
  PowerPC.  I believe the rationale for using a trampoline here
  is to improve performance by avoiding unbalancing of the
  branch predictor's call/return stack.

  However, on PowerPC the bug is dormant as well as it is hidden
  by *another* bug that prevents correct unwinding out of the
  signal trampoline.  This is because the custom CFI for the
  trampoline uses a register number (VSCR) that is not ever used
  by compiler-generated CFI, and that particular register is
  mapped to an invalid number by the current PowerPC DWARF mapper.

The underlying unwinder bug is exposed by the "new" regression failures
in gdb.base/sigstep.exp.  These failures were previously masked by
the fact that GDB was not seeing a valid frame when it tried to unwind
the frames.  The sigstep.exp test is specifically testing stepping into
a signal handler.  With the correct DWARF register mapping in place,
specifically the VSCR mapping, the signal trampoline code now unwinds to a
valid frame exposing the pre-existing bug in how the signal handler on
PowerPC works.  The one line change infrun.c fixes the exiting bug in
the common-code for platforms that use a trampoline to dispatch calls
to the signal handler by not stopping in the SIGTRAMP_FRAME.

Detailed description of the DWARF register mapping fix.

The PowerPC DWARF register mapping is the same for the .eh_frame and
.debug_frame on Linux.  PowerPC uses different mapping for .eh_frame and
.debug_frame on other operating systems.  The current GDB support for
mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum and
rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct for Linux.
The files have some legacy mappings for spe_acc, spefscr, EV which was
removed from GCC in 2017.

This patch adds a two new functions rs6000_linux_dwarf2_reg_to_regnum,
and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c to handle
the DWARF register mappings on Linux.  Function
rs6000_linux_dwarf2_reg_to_regnum is installed for both gdb_dwarf_to_regnum
and gdbarch_stab_reg_to_regnum since the mappings are the same.

The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is updated to
call set_gdbarch_dwarf2_reg_to_regnum map the new function
rs6000_linux_dwarf2_reg_to_regnum for the architecture.  Similarly,
dwarf2_frame_set_adjust_regnum is called to map
rs6000_linux_adjust_frame_regnum into the architecture.

Additional detail on the signal handling fix.

The specific sequence of events for handling a signal on most
architectures is as follows:

  1) Some code is running when a signal arrives.
  2) The kernel handles the signal and dispatches to the handler.
    ...

However on PowerPC the sequence of events is:

  1) Some code is running when a signal arrives.
  2) The kernel handles the signal and dispatches to the trampoline.
  3) The trampoline performs a normal function call to the handler.
      ...

We want the "nexti" to step into, not over, signal handlers invoked by
the kernel.  This is the case for most platforms as the kernel puts a
signal trampoline frame onto the stack to handle proper return after the
handler.  However, on some platforms such as PowerPC, the kernel actually
uses a trampoline to handle *invocation* of the handler.  We do not
want GDB to stop in the SIGTRAMP_FRAME.  The issue is fixed in function
process_event_stop_test by adding a check that the frame is not a
SIGTRAMP_FRAME to the if statement to stop in a subroutine call.  This
prevents GDB from erroneously detecting the trampoline invocation as a
subroutine call.

This patch fixes two regression test failures in gdb.base/store.exp.

The patch then fixes an exposed, dormant, signal handling issue that
is exposed in the signal handling test gdb.base/sigstep.exp.

The patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10 with
no new regressions.  Note, only two of the five failures in store.exp
are fixed.  The remaining three failures are fixed in a following
patch.
---
 gdb/infrun.c         | 13 +++++++++++
 gdb/ppc-linux-tdep.c | 53 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 4730d290442..922d8a6913d 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -7334,8 +7334,21 @@ process_event_stop_test (struct execution_control_state *ecs)
      initial outermost frame, before sp was valid, would
      have code_addr == &_start.  See the comment in frame_id::operator==
      for more.  */
+
+  /* We want "nexti" to step into, not over, signal handlers invoked
+     by the kernel, therefore this subroutine check should not trigger
+     for a signal handler invocation.  On most platforms, this is already
+     not the case, as the kernel puts a signal trampoline frame onto the
+     stack to handle proper return after the handler, and therefore at this
+     point, the current frame is a grandchild of the step frame, not a
+     child.  However, on some platforms, the kernel actually uses a
+     trampoline to handle *invocation* of the handler.  In that case,
+     when executing the first instruction of the trampoline, this check
+     would erroneously detect the trampoline invocation as a subroutine
+     call.  Fix this by checking for SIGTRAMP_FRAME.  */
   if ((get_stack_frame_id (frame)
        != ecs->event_thread->control.step_stack_frame_id)
+      && get_frame_type (frame) != SIGTRAMP_FRAME
       && ((frame_unwind_caller_id (get_current_frame ())
 	   == ecs->event_thread->control.step_stack_frame_id)
 	  && ((ecs->event_thread->control.step_stack_frame_id
diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index 784dafa59db..8d975336fe5 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -83,6 +83,7 @@
 #include "features/rs6000/powerpc-isa207-vsx64l.c"
 #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
 #include "features/rs6000/powerpc-e500l.c"
+#include "dwarf2/frame.h"
 
 /* Shared library operations for PowerPC-Linux.  */
 static struct target_so_ops powerpc_so_ops;
@@ -2088,6 +2089,49 @@ ppc_linux_displaced_step_prepare  (gdbarch *arch, thread_info *thread,
   return per_inferior->disp_step_buf->prepare (thread, displaced_pc);
 }
 
+/* Convert a Dwarf 2 register number to a GDB register number for Linux.  */
+
+static int
+rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
+{
+  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
+
+  if (0 <= num && num <= 31)
+    return tdep->ppc_gp0_regnum + num;
+  else if (32 <= num && num <= 63)
+    return tdep->ppc_fp0_regnum + (num - 32);
+  else if (77 <= num && num < 77 + 32)
+    return tdep->ppc_vr0_regnum + (num - 77);
+  else
+    switch (num)
+      {
+      case 65:
+	return tdep->ppc_lr_regnum;
+      case 66:
+	return tdep->ppc_ctr_regnum;
+      case 76:
+	return tdep->ppc_xer_regnum;
+      case 109:
+	return tdep->ppc_vrsave_regnum;
+      case 110:
+	return tdep->ppc_vrsave_regnum - 1; /* vscr */
+      }
+
+  /* Unknown DWARF register number.  */
+  return -1;
+}
+
+/* Translate a .eh_frame register to DWARF register, or adjust a
+   .debug_frame register.  */
+
+static int
+rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
+				  int eh_frame_p)
+{
+  /* Linux uses the same numbering for .debug_frame numbering as .eh_frame.  */
+  return num;
+}
+
 static void
 ppc_linux_init_abi (struct gdbarch_info info,
 		    struct gdbarch *gdbarch)
@@ -2135,6 +2179,15 @@ ppc_linux_init_abi (struct gdbarch_info info,
   set_gdbarch_stap_is_single_operand (gdbarch, ppc_stap_is_single_operand);
   set_gdbarch_stap_parse_special_token (gdbarch,
 					ppc_stap_parse_special_token);
+  /* Linux DWARF register mapping is different from the other OSes.  */
+  set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
+				    rs6000_linux_dwarf2_reg_to_regnum);
+  /* Note on Linux the mapping for the DWARF registers and the stab registers
+     use the same numbers.  Install rs6000_linux_dwarf2_reg_to_regnum for the
+     stab register mappings as well.  */
+  set_gdbarch_stab_reg_to_regnum (gdbarch,
+				    rs6000_linux_dwarf2_reg_to_regnum);
+  dwarf2_frame_set_adjust_regnum (gdbarch, rs6000_linux_adjust_frame_regnum);
 
   if (tdep->wordsize == 4)
     {
-- 
2.37.2

Re: [PATCH 1/2, ver3] PowerPC, Fix-test-gdb.base-store.exp

[Carl Love]

Ping

Andrew:

Is the updated commit log OK?

              Carl 
-----------------------------------------
On Mon, 2023-10-30 at 10:25 -0700, Carl Love wrote:
> Andrew, Ulrich:
> 
> Per the discussions, the commit message has been updated to make it
> clear that the patch fixes the DWARF register mapping which fixes two
> of the test failures in step.exp.  The fix exposed a dormant issue
> with
> the signal handling on PowerPC.  The underlying issue which is then
> exposed causes the signal handling test sigstep.exp to fail.  The
> test
> sigstep.exp tests stepping into a signal handler.  The patch also
> fixes
> the underlying signal handler issue.  
> 
> This new verion of the patch only updates the commit log to make it
> clear the patch is fixing multiple issues.
> 
> Please let me know if the commit description is clear and acceptable.
> 
> Thanks.
> 
>                             Carl 
> ------------------------------------------------------------
> rs6000, Fix Linux DWARF register mapping
> 
> Overview of issues fixed by the patch.
> 
> The primary issue this patch fixes is the DWARF register mapping for
> Linux.  The changes in ppc-linux-tdep.c fix the DWARF register
> mapping
> issues.  The register mapping issue is responsible for two of the
> five regression bugs seen in gdb.base/store.exp.
> 
> Once the register mapping is fixed, an underlying issue with the
> unwinding
> of the signal trampoline in common-code in ifrun.c was found.  This
> underlying bug is best described by Ulrich in the following
> description.
> 
>   The unwinder bug shows up on platforms where the kernel uses a
> trampoline
>   to dispatch "calls to" the signal handler (not just *returns from*
> the
>   signal handler).  Many platforms use a trampoline for signal
> return, and
>   that is working fine, but the only platform I'm (Ulrich) aware of
> that
>   uses a trampoline for signal handler calls is (recent kernels for)
>   PowerPC.  I believe the rationale for using a trampoline here
>   is to improve performance by avoiding unbalancing of the
>   branch predictor's call/return stack.
> 
>   However, on PowerPC the bug is dormant as well as it is hidden
>   by *another* bug that prevents correct unwinding out of the
>   signal trampoline.  This is because the custom CFI for the
>   trampoline uses a register number (VSCR) that is not ever used
>   by compiler-generated CFI, and that particular register is
>   mapped to an invalid number by the current PowerPC DWARF mapper.
> 
> The underlying unwinder bug is exposed by the "new" regression
> failures
> in gdb.base/sigstep.exp.  These failures were previously masked by
> the fact that GDB was not seeing a valid frame when it tried to
> unwind
> the frames.  The sigstep.exp test is specifically testing stepping
> into
> a signal handler.  With the correct DWARF register mapping in place,
> specifically the VSCR mapping, the signal trampoline code now unwinds
> to a
> valid frame exposing the pre-existing bug in how the signal handler
> on
> PowerPC works.  The one line change infrun.c fixes the exiting bug in
> the common-code for platforms that use a trampoline to dispatch calls
> to the signal handler by not stopping in the SIGTRAMP_FRAME.
> 
> Detailed description of the DWARF register mapping fix.
> 
> The PowerPC DWARF register mapping is the same for the .eh_frame and
> .debug_frame on Linux.  PowerPC uses different mapping for .eh_frame
> and
> .debug_frame on other operating systems.  The current GDB support for
> mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum and
> rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct for
> Linux.
> The files have some legacy mappings for spe_acc, spefscr, EV which
> was
> removed from GCC in 2017.
> 
> This patch adds a two new functions
> rs6000_linux_dwarf2_reg_to_regnum,
> and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c to
> handle
> the DWARF register mappings on Linux.  Function
> rs6000_linux_dwarf2_reg_to_regnum is installed for both
> gdb_dwarf_to_regnum
> and gdbarch_stab_reg_to_regnum since the mappings are the same.
> 
> The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is updated to
> call set_gdbarch_dwarf2_reg_to_regnum map the new function
> rs6000_linux_dwarf2_reg_to_regnum for the architecture.  Similarly,
> dwarf2_frame_set_adjust_regnum is called to map
> rs6000_linux_adjust_frame_regnum into the architecture.
> 
> Additional detail on the signal handling fix.
> 
> The specific sequence of events for handling a signal on most
> architectures is as follows:
> 
>   1) Some code is running when a signal arrives.
>   2) The kernel handles the signal and dispatches to the handler.
>     ...
> 
> However on PowerPC the sequence of events is:
> 
>   1) Some code is running when a signal arrives.
>   2) The kernel handles the signal and dispatches to the trampoline.
>   3) The trampoline performs a normal function call to the handler.
>       ...
> 
> We want the "nexti" to step into, not over, signal handlers invoked
> by
> the kernel.  This is the case for most platforms as the kernel puts a
> signal trampoline frame onto the stack to handle proper return after
> the
> handler.  However, on some platforms such as PowerPC, the kernel
> actually
> uses a trampoline to handle *invocation* of the handler.  We do not
> want GDB to stop in the SIGTRAMP_FRAME.  The issue is fixed in
> function
> process_event_stop_test by adding a check that the frame is not a
> SIGTRAMP_FRAME to the if statement to stop in a subroutine
> call.  This
> prevents GDB from erroneously detecting the trampoline invocation as
> a
> subroutine call.
> 
> This patch fixes two regression test failures in gdb.base/store.exp.
> 
> The patch then fixes an exposed, dormant, signal handling issue that
> is exposed in the signal handling test gdb.base/sigstep.exp.
> 
> The patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10
> with
> no new regressions.  Note, only two of the five failures in store.exp
> are fixed.  The remaining three failures are fixed in a following
> patch.
> ---
>  gdb/infrun.c         | 13 +++++++++++
>  gdb/ppc-linux-tdep.c | 53
> ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 66 insertions(+)
> 
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 4730d290442..922d8a6913d 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -7334,8 +7334,21 @@ process_event_stop_test (struct
> execution_control_state *ecs)
>       initial outermost frame, before sp was valid, would
>       have code_addr == &_start.  See the comment in
> frame_id::operator==
>       for more.  */
> +
> +  /* We want "nexti" to step into, not over, signal handlers invoked
> +     by the kernel, therefore this subroutine check should not
> trigger
> +     for a signal handler invocation.  On most platforms, this is
> already
> +     not the case, as the kernel puts a signal trampoline frame onto
> the
> +     stack to handle proper return after the handler, and therefore
> at this
> +     point, the current frame is a grandchild of the step frame, not
> a
> +     child.  However, on some platforms, the kernel actually uses a
> +     trampoline to handle *invocation* of the handler.  In that
> case,
> +     when executing the first instruction of the trampoline, this
> check
> +     would erroneously detect the trampoline invocation as a
> subroutine
> +     call.  Fix this by checking for SIGTRAMP_FRAME.  */
>    if ((get_stack_frame_id (frame)
>         != ecs->event_thread->control.step_stack_frame_id)
> +      && get_frame_type (frame) != SIGTRAMP_FRAME
>        && ((frame_unwind_caller_id (get_current_frame ())
>  	   == ecs->event_thread->control.step_stack_frame_id)
>  	  && ((ecs->event_thread->control.step_stack_frame_id
> diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> index 784dafa59db..8d975336fe5 100644
> --- a/gdb/ppc-linux-tdep.c
> +++ b/gdb/ppc-linux-tdep.c
> @@ -83,6 +83,7 @@
>  #include "features/rs6000/powerpc-isa207-vsx64l.c"
>  #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
>  #include "features/rs6000/powerpc-e500l.c"
> +#include "dwarf2/frame.h"
>  
>  /* Shared library operations for PowerPC-Linux.  */
>  static struct target_so_ops powerpc_so_ops;
> @@ -2088,6 +2089,49 @@ ppc_linux_displaced_step_prepare  (gdbarch
> *arch, thread_info *thread,
>    return per_inferior->disp_step_buf->prepare (thread,
> displaced_pc);
>  }
>  
> +/* Convert a Dwarf 2 register number to a GDB register number for
> Linux.  */
> +
> +static int
> +rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
> +{
> +  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
> +
> +  if (0 <= num && num <= 31)
> +    return tdep->ppc_gp0_regnum + num;
> +  else if (32 <= num && num <= 63)
> +    return tdep->ppc_fp0_regnum + (num - 32);
> +  else if (77 <= num && num < 77 + 32)
> +    return tdep->ppc_vr0_regnum + (num - 77);
> +  else
> +    switch (num)
> +      {
> +      case 65:
> +	return tdep->ppc_lr_regnum;
> +      case 66:
> +	return tdep->ppc_ctr_regnum;
> +      case 76:
> +	return tdep->ppc_xer_regnum;
> +      case 109:
> +	return tdep->ppc_vrsave_regnum;
> +      case 110:
> +	return tdep->ppc_vrsave_regnum - 1; /* vscr */
> +      }
> +
> +  /* Unknown DWARF register number.  */
> +  return -1;
> +}
> +
> +/* Translate a .eh_frame register to DWARF register, or adjust a
> +   .debug_frame register.  */
> +
> +static int
> +rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
> +				  int eh_frame_p)
> +{
> +  /* Linux uses the same numbering for .debug_frame numbering as
> .eh_frame.  */
> +  return num;
> +}
> +
>  static void
>  ppc_linux_init_abi (struct gdbarch_info info,
>  		    struct gdbarch *gdbarch)
> @@ -2135,6 +2179,15 @@ ppc_linux_init_abi (struct gdbarch_info info,
>    set_gdbarch_stap_is_single_operand (gdbarch,
> ppc_stap_is_single_operand);
>    set_gdbarch_stap_parse_special_token (gdbarch,
>  					ppc_stap_parse_special_token);
> +  /* Linux DWARF register mapping is different from the other
> OSes.  */
> +  set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  /* Note on Linux the mapping for the DWARF registers and the stab
> registers
> +     use the same numbers.  Install
> rs6000_linux_dwarf2_reg_to_regnum for the
> +     stab register mappings as well.  */
> +  set_gdbarch_stab_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  dwarf2_frame_set_adjust_regnum (gdbarch,
> rs6000_linux_adjust_frame_regnum);
>  
>    if (tdep->wordsize == 4)
>      {

Re: [PATCH 1/2, ver3] PowerPC, Fix-test-gdb.base-store.exp

[Andrew Burgess]

Carl Love <cel@linux.ibm.com> writes:

> Andrew, Ulrich:
>
> Per the discussions, the commit message has been updated to make it
> clear that the patch fixes the DWARF register mapping which fixes two
> of the test failures in step.exp.  The fix exposed a dormant issue with
> the signal handling on PowerPC.  The underlying issue which is then
> exposed causes the signal handling test sigstep.exp to fail.  The test
> sigstep.exp tests stepping into a signal handler.  The patch also fixes
> the underlying signal handler issue.  
>
> This new verion of the patch only updates the commit log to make it
> clear the patch is fixing multiple issues.
>
> Please let me know if the commit description is clear and acceptable.
>
> Thanks.
>
>                             Carl 
> ------------------------------------------------------------
> rs6000, Fix Linux DWARF register mapping
>
> Overview of issues fixed by the patch.
>
> The primary issue this patch fixes is the DWARF register mapping for
> Linux.  The changes in ppc-linux-tdep.c fix the DWARF register mapping
> issues.  The register mapping issue is responsible for two of the
> five regression bugs seen in gdb.base/store.exp.
>
> Once the register mapping is fixed, an underlying issue with the unwinding
> of the signal trampoline in common-code in ifrun.c was found.  This
> underlying bug is best described by Ulrich in the following description.
>
>   The unwinder bug shows up on platforms where the kernel uses a trampoline
>   to dispatch "calls to" the signal handler (not just *returns from* the
>   signal handler).  Many platforms use a trampoline for signal return, and
>   that is working fine, but the only platform I'm (Ulrich) aware of that
>   uses a trampoline for signal handler calls is (recent kernels for)
>   PowerPC.  I believe the rationale for using a trampoline here
>   is to improve performance by avoiding unbalancing of the
>   branch predictor's call/return stack.
>
>   However, on PowerPC the bug is dormant as well as it is hidden
>   by *another* bug that prevents correct unwinding out of the
>   signal trampoline.  This is because the custom CFI for the
>   trampoline uses a register number (VSCR) that is not ever used
>   by compiler-generated CFI, and that particular register is
>   mapped to an invalid number by the current PowerPC DWARF mapper.
>
> The underlying unwinder bug is exposed by the "new" regression failures
> in gdb.base/sigstep.exp.  These failures were previously masked by
> the fact that GDB was not seeing a valid frame when it tried to unwind
> the frames.  The sigstep.exp test is specifically testing stepping into
> a signal handler.  With the correct DWARF register mapping in place,
> specifically the VSCR mapping, the signal trampoline code now unwinds to a
> valid frame exposing the pre-existing bug in how the signal handler on
> PowerPC works.  The one line change infrun.c fixes the exiting bug in
> the common-code for platforms that use a trampoline to dispatch calls
> to the signal handler by not stopping in the SIGTRAMP_FRAME.
>
> Detailed description of the DWARF register mapping fix.
>
> The PowerPC DWARF register mapping is the same for the .eh_frame and
> .debug_frame on Linux.  PowerPC uses different mapping for .eh_frame and
> .debug_frame on other operating systems.  The current GDB support for
> mapping the DWARF registers in rs6000_linux_dwarf2_reg_to_regnum and
> rs6000_adjust_frame_regnum file gdb/rs6000-tdep.c is not correct for Linux.
> The files have some legacy mappings for spe_acc, spefscr, EV which was
> removed from GCC in 2017.
>
> This patch adds a two new functions rs6000_linux_dwarf2_reg_to_regnum,
> and rs6000_linux_adjust_frame_regnum in file gdb/ppc-linux-tdep.c to handle
> the DWARF register mappings on Linux.  Function
> rs6000_linux_dwarf2_reg_to_regnum is installed for both gdb_dwarf_to_regnum
> and gdbarch_stab_reg_to_regnum since the mappings are the same.
>
> The ppc_linux_init_abi function in gdb/ppc-linux-tdep.c is updated to
> call set_gdbarch_dwarf2_reg_to_regnum map the new function
> rs6000_linux_dwarf2_reg_to_regnum for the architecture.  Similarly,
> dwarf2_frame_set_adjust_regnum is called to map
> rs6000_linux_adjust_frame_regnum into the architecture.
>
> Additional detail on the signal handling fix.
>
> The specific sequence of events for handling a signal on most
> architectures is as follows:
>
>   1) Some code is running when a signal arrives.
>   2) The kernel handles the signal and dispatches to the handler.
>     ...
>
> However on PowerPC the sequence of events is:
>
>   1) Some code is running when a signal arrives.
>   2) The kernel handles the signal and dispatches to the trampoline.
>   3) The trampoline performs a normal function call to the handler.
>       ...
>
> We want the "nexti" to step into, not over, signal handlers invoked by
> the kernel.  This is the case for most platforms as the kernel puts a
> signal trampoline frame onto the stack to handle proper return after the
> handler.  However, on some platforms such as PowerPC, the kernel actually
> uses a trampoline to handle *invocation* of the handler.  We do not
> want GDB to stop in the SIGTRAMP_FRAME.  The issue is fixed in function
> process_event_stop_test by adding a check that the frame is not a
> SIGTRAMP_FRAME to the if statement to stop in a subroutine call.  This
> prevents GDB from erroneously detecting the trampoline invocation as a
> subroutine call.
>
> This patch fixes two regression test failures in gdb.base/store.exp.
>
> The patch then fixes an exposed, dormant, signal handling issue that
> is exposed in the signal handling test gdb.base/sigstep.exp.
>
> The patch has been tested on Power 8 LE/BE, Power 9 LE/BE, Power 10 with
> no new regressions.  Note, only two of the five failures in store.exp
> are fixed.  The remaining three failures are fixed in a following
> patch.

Carl,

Sorry for the slow delay, I had to find some time to play with this a
little.  But thanks to the expanded explanation, it's now clear what's
going on.  This all looks great.

Approved-By: Andrew Burgess <aburgess@redhat.com>

Thanks,
Andrew


> ---
>  gdb/infrun.c         | 13 +++++++++++
>  gdb/ppc-linux-tdep.c | 53 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 66 insertions(+)
>
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 4730d290442..922d8a6913d 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -7334,8 +7334,21 @@ process_event_stop_test (struct execution_control_state *ecs)
>       initial outermost frame, before sp was valid, would
>       have code_addr == &_start.  See the comment in frame_id::operator==
>       for more.  */
> +
> +  /* We want "nexti" to step into, not over, signal handlers invoked
> +     by the kernel, therefore this subroutine check should not trigger
> +     for a signal handler invocation.  On most platforms, this is already
> +     not the case, as the kernel puts a signal trampoline frame onto the
> +     stack to handle proper return after the handler, and therefore at this
> +     point, the current frame is a grandchild of the step frame, not a
> +     child.  However, on some platforms, the kernel actually uses a
> +     trampoline to handle *invocation* of the handler.  In that case,
> +     when executing the first instruction of the trampoline, this check
> +     would erroneously detect the trampoline invocation as a subroutine
> +     call.  Fix this by checking for SIGTRAMP_FRAME.  */
>    if ((get_stack_frame_id (frame)
>         != ecs->event_thread->control.step_stack_frame_id)
> +      && get_frame_type (frame) != SIGTRAMP_FRAME
>        && ((frame_unwind_caller_id (get_current_frame ())
>  	   == ecs->event_thread->control.step_stack_frame_id)
>  	  && ((ecs->event_thread->control.step_stack_frame_id
> diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
> index 784dafa59db..8d975336fe5 100644
> --- a/gdb/ppc-linux-tdep.c
> +++ b/gdb/ppc-linux-tdep.c
> @@ -83,6 +83,7 @@
>  #include "features/rs6000/powerpc-isa207-vsx64l.c"
>  #include "features/rs6000/powerpc-isa207-htm-vsx64l.c"
>  #include "features/rs6000/powerpc-e500l.c"
> +#include "dwarf2/frame.h"
>  
>  /* Shared library operations for PowerPC-Linux.  */
>  static struct target_so_ops powerpc_so_ops;
> @@ -2088,6 +2089,49 @@ ppc_linux_displaced_step_prepare  (gdbarch *arch, thread_info *thread,
>    return per_inferior->disp_step_buf->prepare (thread, displaced_pc);
>  }
>  
> +/* Convert a Dwarf 2 register number to a GDB register number for Linux.  */
> +
> +static int
> +rs6000_linux_dwarf2_reg_to_regnum (struct gdbarch *gdbarch, int num)
> +{
> +  ppc_gdbarch_tdep *tdep = gdbarch_tdep<ppc_gdbarch_tdep>(gdbarch);
> +
> +  if (0 <= num && num <= 31)
> +    return tdep->ppc_gp0_regnum + num;
> +  else if (32 <= num && num <= 63)
> +    return tdep->ppc_fp0_regnum + (num - 32);
> +  else if (77 <= num && num < 77 + 32)
> +    return tdep->ppc_vr0_regnum + (num - 77);
> +  else
> +    switch (num)
> +      {
> +      case 65:
> +	return tdep->ppc_lr_regnum;
> +      case 66:
> +	return tdep->ppc_ctr_regnum;
> +      case 76:
> +	return tdep->ppc_xer_regnum;
> +      case 109:
> +	return tdep->ppc_vrsave_regnum;
> +      case 110:
> +	return tdep->ppc_vrsave_regnum - 1; /* vscr */
> +      }
> +
> +  /* Unknown DWARF register number.  */
> +  return -1;
> +}
> +
> +/* Translate a .eh_frame register to DWARF register, or adjust a
> +   .debug_frame register.  */
> +
> +static int
> +rs6000_linux_adjust_frame_regnum (struct gdbarch *gdbarch, int num,
> +				  int eh_frame_p)
> +{
> +  /* Linux uses the same numbering for .debug_frame numbering as .eh_frame.  */
> +  return num;
> +}
> +
>  static void
>  ppc_linux_init_abi (struct gdbarch_info info,
>  		    struct gdbarch *gdbarch)
> @@ -2135,6 +2179,15 @@ ppc_linux_init_abi (struct gdbarch_info info,
>    set_gdbarch_stap_is_single_operand (gdbarch, ppc_stap_is_single_operand);
>    set_gdbarch_stap_parse_special_token (gdbarch,
>  					ppc_stap_parse_special_token);
> +  /* Linux DWARF register mapping is different from the other OSes.  */
> +  set_gdbarch_dwarf2_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  /* Note on Linux the mapping for the DWARF registers and the stab registers
> +     use the same numbers.  Install rs6000_linux_dwarf2_reg_to_regnum for the
> +     stab register mappings as well.  */
> +  set_gdbarch_stab_reg_to_regnum (gdbarch,
> +				    rs6000_linux_dwarf2_reg_to_regnum);
> +  dwarf2_frame_set_adjust_regnum (gdbarch, rs6000_linux_adjust_frame_regnum);
>  
>    if (tdep->wordsize == 4)
>      {
> -- 
> 2.37.2