Re: [PATCH ver 2] PowerPC: fix _Float128 type output string

[Carl Love <cel@us.ibm.com>]

Kevin, GDB maintainers:

I have updated the patch with an additional comment in function
read_type to explain what the if statement is doing per Kevin's
feedback.

Please let me know if the patch is acceptable for mainline.  Thanks.

                         Carl

P.S. I am resending this as the first message bounced on Kevin's
address.

-----------------------------------------------------
PowerPC: fix _Float128 type output string

PowerPC supports two 128-bit floating point formats, the IBM long double
and IEEE 128-bit float.  The issue is the DWARF information does not
distinguish between the two.  There have been proposals of how to extend
the DWARF information as discussed in

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104194

but has not been fully implemented.

GCC introduced the _Float128 internal type as a work around for the issue.
The workaround is not transparent to GDB.  The internal _Float128 type
name is printed rather then the user specified long double type.  This
patch adds a new gdbarch method to allow PowerPC to detect the GCC
workaround.  The workaround checks for "_Float128" name when reading the
base typedef from the die_info.  If the workaround is detected, the type
and format fields from the _Float128 typedef are copied to the long
double typedef.  The same is done for the complex long double typedef.

This patch fixes 74 regression test failures in
gdb.base/whatis-ptype-typedefs.exp on PowerPC with IEEE float 128 as the
default on GCC.  It fixes one regression test failure in
gdb.base/complex-parts.exp.

The patch has been tested on Power 10 where GCC defaults to IEEE Float
128-bit and on Power 10 where GCC defaults to the IBM 128-bit float.  The
patch as also been tested on X86-64 with no new regression failures.
---
 gdb/arch-utils.c          |  7 +++++++
 gdb/arch-utils.h          |  5 +++++
 gdb/dwarf2/read.c         | 23 +++++++++++++++++++----
 gdb/gdbarch-gen.h         |  8 ++++++++
 gdb/gdbarch.c             | 22 ++++++++++++++++++++++
 gdb/gdbarch_components.py | 19 +++++++++++++++++++
 gdb/ppc-linux-tdep.c      | 36 ++++++++++++++++++++++++++++++++++++
 gdb/ppc-tdep.h            |  3 +++
 8 files changed, 119 insertions(+), 4 deletions(-)

diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
index e3af9ce2dbc..997a292e9ef 100644
--- a/gdb/arch-utils.c
+++ b/gdb/arch-utils.c
@@ -1098,6 +1098,13 @@ default_get_return_buf_addr (struct type *val_type, frame_info_ptr cur_frame)
   return 0;
 }
 
+bool
+default_dwarf2_omit_typedef_p (struct type *target_type, const char *producer,
+			       const char *name)
+{
+  return false;
+}
+
 /* Non-zero if we want to trace architecture code.  */
 
 #ifndef GDBARCH_DEBUG
diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h
index 56690f0fd43..fc0c0b16793 100644
--- a/gdb/arch-utils.h
+++ b/gdb/arch-utils.h
@@ -309,6 +309,11 @@ extern void default_read_core_file_mappings
 extern CORE_ADDR default_get_return_buf_addr (struct type *val_typegdbarch,
 					      frame_info_ptr cur_frame);
 
+/* Default implementation of gdbaarch default_dwarf2_omit_typedef_p method.  */
+extern bool default_dwarf2_omit_typedef_p (struct type *target_type,
+					   const char *producer,
+					   const char *name);
+
 extern enum return_value_convention default_gdbarch_return_value
      (struct gdbarch *gdbarch, struct value *function, struct type *valtype,
       struct regcache *regcache, struct value **read_value,
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index c9208a097bf..19654f408ee 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -14702,14 +14702,29 @@ static struct type *
 read_typedef (struct die_info *die, struct dwarf2_cu *cu)
 {
   struct objfile *objfile = cu->per_objfile->objfile;
-  const char *name = NULL;
-  struct type *this_type, *target_type;
+  const char *name = dwarf2_full_name (NULL, die, cu);
+  struct type *this_type;
+  struct gdbarch *gdbarch = objfile->arch ();
+  struct type *target_type = die_type (die, cu);
+
+  if (gdbarch_dwarf2_omit_typedef_p (gdbarch, target_type, cu->producer, name))
+    {
+      /* The long double is defined as a base type in C.  GCC creates a long
+	 double typedef with target-type _Float128 for the long double to
+	 identify it as the IEEE Float128 value.  This is a GCC hack since the
+	 DWARF doesn't distinquish between the IBM long double and IEEE
+	 128-bit float.	 Replace the GCC workaround for the long double
+	 typedef with the actual type information copied from the target-type
+	 with the correct long double base type name.  */
+      this_type = copy_type (target_type);
+      this_type->set_name (name);
+      set_die_type (die, this_type, cu);
+      return this_type;
+    }
 
-  name = dwarf2_full_name (NULL, die, cu);
   this_type = type_allocator (objfile).new_type (TYPE_CODE_TYPEDEF, 0, name);
   this_type->set_target_is_stub (true);
   set_die_type (die, this_type, cu);
-  target_type = die_type (die, cu);
   if (target_type != this_type)
     this_type->set_target_type (target_type);
   else
diff --git a/gdb/gdbarch-gen.h b/gdb/gdbarch-gen.h
index a3fc0b9272b..3d8aafd5ea6 100644
--- a/gdb/gdbarch-gen.h
+++ b/gdb/gdbarch-gen.h
@@ -468,6 +468,14 @@ typedef CORE_ADDR (gdbarch_get_return_buf_addr_ftype) (struct type *val_type, fr
 extern CORE_ADDR gdbarch_get_return_buf_addr (struct gdbarch *gdbarch, struct type *val_type, frame_info_ptr cur_frame);
 extern void set_gdbarch_get_return_buf_addr (struct gdbarch *gdbarch, gdbarch_get_return_buf_addr_ftype *get_return_buf_addr);
 
+/* Return true if the typedef record needs to be replaced.".
+
+   Return 0 by default */
+
+typedef bool (gdbarch_dwarf2_omit_typedef_p_ftype) (struct type *target_type, const char *producer, const char *name);
+extern bool gdbarch_dwarf2_omit_typedef_p (struct gdbarch *gdbarch, struct type *target_type, const char *producer, const char *name);
+extern void set_gdbarch_dwarf2_omit_typedef_p (struct gdbarch *gdbarch, gdbarch_dwarf2_omit_typedef_p_ftype *dwarf2_omit_typedef_p);
+
 /* Return true if the return value of function is stored in the first hidden
    parameter.  In theory, this feature should be language-dependent, specified
    by language and its ABI, such as C++.  Unfortunately, compiler may
diff --git a/gdb/gdbarch.c b/gdb/gdbarch.c
index b676e346fd0..00e7191653a 100644
--- a/gdb/gdbarch.c
+++ b/gdb/gdbarch.c
@@ -114,6 +114,7 @@ struct gdbarch
   gdbarch_return_value_ftype *return_value = nullptr;
   gdbarch_return_value_as_value_ftype *return_value_as_value = default_gdbarch_return_value;
   gdbarch_get_return_buf_addr_ftype *get_return_buf_addr = default_get_return_buf_addr;
+  gdbarch_dwarf2_omit_typedef_p_ftype *dwarf2_omit_typedef_p = default_dwarf2_omit_typedef_p;
   gdbarch_return_in_first_hidden_param_p_ftype *return_in_first_hidden_param_p = default_return_in_first_hidden_param_p;
   gdbarch_skip_prologue_ftype *skip_prologue = nullptr;
   gdbarch_skip_main_prologue_ftype *skip_main_prologue = nullptr;
@@ -370,6 +371,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   if ((gdbarch->return_value_as_value == default_gdbarch_return_value) == (gdbarch->return_value == nullptr))
     log.puts ("\n\treturn_value_as_value");
   /* Skip verify of get_return_buf_addr, invalid_p == 0 */
+  /* Skip verify of dwarf2_omit_typedef_p, invalid_p == 0 */
   /* Skip verify of return_in_first_hidden_param_p, invalid_p == 0 */
   if (gdbarch->skip_prologue == 0)
     log.puts ("\n\tskip_prologue");
@@ -788,6 +790,9 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
   gdb_printf (file,
 	      "gdbarch_dump: get_return_buf_addr = <%s>\n",
 	      host_address_to_string (gdbarch->get_return_buf_addr));
+  gdb_printf (file,
+	      "gdbarch_dump: dwarf2_omit_typedef_p = <%s>\n",
+	      host_address_to_string (gdbarch->dwarf2_omit_typedef_p));
   gdb_printf (file,
 	      "gdbarch_dump: return_in_first_hidden_param_p = <%s>\n",
 	      host_address_to_string (gdbarch->return_in_first_hidden_param_p));
@@ -2617,6 +2622,23 @@ set_gdbarch_get_return_buf_addr (struct gdbarch *gdbarch,
   gdbarch->get_return_buf_addr = get_return_buf_addr;
 }
 
+bool
+gdbarch_dwarf2_omit_typedef_p (struct gdbarch *gdbarch, struct type *target_type, const char *producer, const char *name)
+{
+  gdb_assert (gdbarch != NULL);
+  gdb_assert (gdbarch->dwarf2_omit_typedef_p != NULL);
+  if (gdbarch_debug >= 2)
+    gdb_printf (gdb_stdlog, "gdbarch_dwarf2_omit_typedef_p called\n");
+  return gdbarch->dwarf2_omit_typedef_p (target_type, producer, name);
+}
+
+void
+set_gdbarch_dwarf2_omit_typedef_p (struct gdbarch *gdbarch,
+				   gdbarch_dwarf2_omit_typedef_p_ftype dwarf2_omit_typedef_p)
+{
+  gdbarch->dwarf2_omit_typedef_p = dwarf2_omit_typedef_p;
+}
+
 int
 gdbarch_return_in_first_hidden_param_p (struct gdbarch *gdbarch, struct type *type)
 {
diff --git a/gdb/gdbarch_components.py b/gdb/gdbarch_components.py
index 2b1a2b4f602..7a64d9e006b 100644
--- a/gdb/gdbarch_components.py
+++ b/gdb/gdbarch_components.py
@@ -901,6 +901,25 @@ May return 0 when unable to determine that address.""",
     invalid=False,
 )
 
+
+# The DWARF info currently does not distinquish between IEEE 128-bit floating
+# point values and the IBM 128-bit floating point format.  GCC has an internal
+# hack that uses the _Float128 base typdef for IEEE 128-bit float values.  The
+# following method is used to "fix" the long double typedef so the _Float128
+# name is not printed.
+Function(
+    comment="""
+Return true if the typedef record needs to be replaced.".
+
+Return 0 by default""",
+    type="bool",
+    name="dwarf2_omit_typedef_p",
+    params=[("struct type *", "target_type"), ("const char *", "producer"),
+            ("const char *", "name")],
+    predefault="default_dwarf2_omit_typedef_p",
+    invalid=False,
+)
+
 Method(
     comment="""
 Return true if the return value of function is stored in the first hidden
diff --git a/gdb/ppc-linux-tdep.c b/gdb/ppc-linux-tdep.c
index fcddb2008a0..7f5f97b6510 100644
--- a/gdb/ppc-linux-tdep.c
+++ b/gdb/ppc-linux-tdep.c
@@ -62,6 +62,7 @@
 #include "user-regs.h"
 #include <ctype.h>
 #include "elf-bfd.h"
+#include "producer.h"
 
 #include "features/rs6000/powerpc-32l.c"
 #include "features/rs6000/powerpc-altivec32l.c"
@@ -2006,6 +2007,38 @@ ppc_floatformat_for_type (struct gdbarch *gdbarch,
   return default_floatformat_for_type (gdbarch, name, len);
 }
 
+bool
+linux_dwarf2_omit_typedef_p (struct type *target_type,
+			     const char *producer, const char *name)
+{
+  int gcc_major, gcc_minor;
+
+  if (producer_is_gcc (producer, &gcc_major, &gcc_minor))
+    {
+      if ((target_type->code () == TYPE_CODE_FLT
+	   || target_type->code () == TYPE_CODE_COMPLEX)
+	  && (strcmp (name, "long double") == 0
+	      || strcmp (name, "complex long double") == 0))
+	{
+	  /* IEEE 128-bit floating point and IBM long double are two
+	     encodings for 128-bit values.  The DWARF debug data can't
+	     distinguish between them.  See bugzilla:
+	     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104194
+
+	     A GCC hack was introduced to still allow the debugger to identify
+	     the case where "long double" uses the IEEE 128-bit floating point
+	     format: GCC will emit a bogus DWARF type record pretending that
+	     "long double" is a typedef alias for the _Float128 type.
+
+	     This hack should not be visible to the GDB user, so we replace
+	     this bogus typedef by a normal floating-point type, copying the
+	     format information from the target type of the bogus typedef.  */
+	  return true;
+	}
+    }
+  return false;
+}
+
 /* Specify the powerpc64le target triplet.
    This can be variations of
 	ppc64le-{distro}-linux-gcc
@@ -2083,6 +2116,9 @@ ppc_linux_init_abi (struct gdbarch_info info,
   /* Support for floating-point data type variants.  */
   set_gdbarch_floatformat_for_type (gdbarch, ppc_floatformat_for_type);
 
+  /* Support for replacing typedef record.  */
+  set_gdbarch_dwarf2_omit_typedef_p (gdbarch, linux_dwarf2_omit_typedef_p);
+
   /* Handle inferior calls during interrupted system calls.  */
   set_gdbarch_write_pc (gdbarch, ppc_linux_write_pc);
 
diff --git a/gdb/ppc-tdep.h b/gdb/ppc-tdep.h
index db4e53205a6..f078b3d45ab 100644
--- a/gdb/ppc-tdep.h
+++ b/gdb/ppc-tdep.h
@@ -176,6 +176,9 @@ extern void ppc_collect_vsxregset (const struct regset *regset,
 				  int regnum, void *vsxregs, size_t len);
 
 extern CORE_ADDR ppc64_sysv_get_return_buf_addr (type*, frame_info_ptr);
+extern bool linux_dwarf2_omit_typedef_p (struct type *target_type,
+					 const char *producer,
+					 const char *name);
 
 /* Private data that this module attaches to struct gdbarch.  */
 
-- 
2.37.2