Re: [PATCH v2] libdw/libdwfl: Add API for accessing registers

[Mark Wielaard <mark@klomp.org>]

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Hi,

On Fri, Jul 29, 2022 at 11:18:45PM +0800, Di Chen wrote:
> Re-pushed for fixing run-backtrace-core-sparc.sh failure which resulted
> from some wrong register number.

Thanks. Good the try check caught that copy/paste issue, I would have
probably missed it on review.

> On Fri, Jul 29, 2022 at 9:27 PM Di Chen <dichen@redhat.com> wrote:
> 
> > Thanks for the review, Mark.
> >
> > Re-pushed a patch for it.
> >
> > 1. NEWS entry added.
> > 2. __libdwfl_frame_reg_get/dwfl_frame_reg updated with return int.
> > 3. New DWFL_ERROR added: REGISTER_VAL_UNKNOWN.

Thanks, this looks good.  I added ChangeLog entries while
reviewing. Not code issues found. I did change invalud -> invalid in
the comments and tweaked the comment on __libdwfl_frame_reg_get to
explain no error code is ever set. Pushed with those changes.

Cheers,

Mark

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From ccc157dc2b96e47d6d1bbb1b066ecbea4975051b Mon Sep 17 00:00:00 2001
From: Di Chen <dichen@redhat.com>
Date: Thu, 28 Jul 2022 16:31:05 +0800
Subject: [PATCH] libdwfl: Add new function dwfl_frame_reg

Dwfl has most of the infrastructure to keep the full unwind state,
including the state of unwound registers per frame using
Dwfl_Thread_Callbacks. But there is no public API to access the state,
except for the PC (dwfl_frame_pc).

This commit adds a new function dwfl_frame_reg to get the value of the
DWARF register number in the given frame.

https://sourceware.org/bugzilla/show_bug.cgi?id=28579

Signed-off-by: Di Chen <dichen@redhat.com>
---
 ChangeLog                   |  4 ++++
 NEWS                        |  1 +
 libdw/ChangeLog             |  4 ++++
 libdw/libdw.map             |  1 +
 libdwfl/ChangeLog           | 15 ++++++++++++++
 libdwfl/dwfl_frame_regs.c   | 12 +++++++++++
 libdwfl/frame_unwind.c      | 40 ++++++++++++++-----------------------
 libdwfl/libdwfl.h           |  6 ++++++
 libdwfl/libdwflP.h          | 10 +++++++---
 libdwfl/linux-core-attach.c |  2 +-
 10 files changed, 66 insertions(+), 29 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index eb2a35f5..0ececcc9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2022-07-28  Di Chen  <dichen@redhat.com>
+
+	* NEWS: Add dwfl_frame_reg.
+
 2022-07-13  Mark Wielaard  <mark@klomp.org>
 
 	* NEWS: Add dwfl_get_debuginfod_client.
diff --git a/NEWS b/NEWS
index 392f2edc..82c86cb6 100644
--- a/NEWS
+++ b/NEWS
@@ -3,6 +3,7 @@ Version 0.188 some time after 0.187
 debuginfod: Add --disable-source-scan option.
 
 libdwfl: Add new function dwfl_get_debuginfod_client.
+         Add new function dwfl_frame_reg.
 
 Version 0.187
 
diff --git a/libdw/ChangeLog b/libdw/ChangeLog
index 6a8f7e51..c9d94e0b 100644
--- a/libdw/ChangeLog
+++ b/libdw/ChangeLog
@@ -1,3 +1,7 @@
+2022-07-28  Di Chen  <dichen@redhat.com>
+
+	* libdw.map (ELFUTILS_0.188): Add dwfl_frame_reg.
+
 2022-07-13  Mark Wielaard  <mark@klomp.org>
 
 	* libdw.map (ELFUTILS_0.187): Renamed to...
diff --git a/libdw/libdw.map b/libdw/libdw.map
index 6da25561..8f393438 100644
--- a/libdw/libdw.map
+++ b/libdw/libdw.map
@@ -370,4 +370,5 @@ ELFUTILS_0.186 {
 ELFUTILS_0.188 {
   global:
     dwfl_get_debuginfod_client;
+    dwfl_frame_reg;
 } ELFUTILS_0.186;
diff --git a/libdwfl/ChangeLog b/libdwfl/ChangeLog
index acdaa013..30f30b14 100644
--- a/libdwfl/ChangeLog
+++ b/libdwfl/ChangeLog
@@ -1,3 +1,18 @@
+2022-07-28  Di Chen  <dichen@redhat.com>
+
+	* libdwfl.h (dwfl_frame_reg): New function.
+	* libdwflP.h (DWFL_E_REGISTER_VAL_UNKNOWN): New error code.
+	(__libdwfl_frame_reg_get): Return an int.
+	(dwfl_frame_reg): INTDECL.
+	* dwfl_frame_regs.c (dwfl_frame_reg): New function.
+	* frame_unwind.c (__libdwfl_frame_reg_get): Return an int.
+	(state_get_reg): Removed.
+	(expr_eval): Use INTUSE (dwfl_frame_reg) instead of state_get_reg.
+	(handle_cfi): Likewise.
+	(getfunc): Likewise.
+	* linux-core-attach.c (core_set_initial_registers): Check
+	__libdwfl_frame_reg_get returns zero.
+
 2022-07-28  Mark Wielaard  <mark@klomp.org>
 
 	* core-file.c (elf_begin_rand): Replace struct ar_hdr h with
diff --git a/libdwfl/dwfl_frame_regs.c b/libdwfl/dwfl_frame_regs.c
index 83b1abef..a4bd3884 100644
--- a/libdwfl/dwfl_frame_regs.c
+++ b/libdwfl/dwfl_frame_regs.c
@@ -59,3 +59,15 @@ dwfl_thread_state_register_pc (Dwfl_Thread *thread, Dwarf_Word pc)
   state->pc_state = DWFL_FRAME_STATE_PC_SET;
 }
 INTDEF(dwfl_thread_state_register_pc)
+
+int
+dwfl_frame_reg (Dwfl_Frame *state, unsigned regno, Dwarf_Word *val)
+{
+  int res = __libdwfl_frame_reg_get (state, regno, val);
+  if (res == -1)
+      __libdwfl_seterrno (DWFL_E_INVALID_REGISTER);
+  else if (res == 1)
+      __libdwfl_seterrno (DWFL_E_REGISTER_VAL_UNKNOWN);
+  return res;
+}
+INTDEF(dwfl_frame_reg)
diff --git a/libdwfl/frame_unwind.c b/libdwfl/frame_unwind.c
index 9ac33833..8185d84b 100644
--- a/libdwfl/frame_unwind.c
+++ b/libdwfl/frame_unwind.c
@@ -43,21 +43,21 @@
    error.  */
 #define DWARF_EXPR_STEPS_MAX 0x1000
 
-bool
+int
 internal_function
 __libdwfl_frame_reg_get (Dwfl_Frame *state, unsigned regno, Dwarf_Addr *val)
 {
   Ebl *ebl = state->thread->process->ebl;
   if (! ebl_dwarf_to_regno (ebl, &regno))
-    return false;
+    return -1;
   if (regno >= ebl_frame_nregs (ebl))
-    return false;
+    return -1;
   if ((state->regs_set[regno / sizeof (*state->regs_set) / 8]
        & ((uint64_t) 1U << (regno % (sizeof (*state->regs_set) * 8)))) == 0)
-    return false;
+    return 1;
   if (val)
     *val = state->regs[regno];
-  return true;
+  return 0;
 }
 
 bool
@@ -78,17 +78,6 @@ __libdwfl_frame_reg_set (Dwfl_Frame *state, unsigned regno, Dwarf_Addr val)
   return true;
 }
 
-static bool
-state_get_reg (Dwfl_Frame *state, unsigned regno, Dwarf_Addr *val)
-{
-  if (! __libdwfl_frame_reg_get (state, regno, val))
-    {
-      __libdwfl_seterrno (DWFL_E_INVALID_REGISTER);
-      return false;
-    }
-  return true;
-}
-
 static int
 bra_compar (const void *key_voidp, const void *elem_voidp)
 {
@@ -211,7 +200,7 @@ expr_eval (Dwfl_Frame *state, Dwarf_Frame *frame, const Dwarf_Op *ops,
 	    }
 	  break;
 	case DW_OP_reg0 ... DW_OP_reg31:
-	  if (! state_get_reg (state, op->atom - DW_OP_reg0, &val1)
+	  if (INTUSE (dwfl_frame_reg) (state, op->atom - DW_OP_reg0, &val1) != 0
 	      || ! push (val1))
 	    {
 	      free (stack.addrs);
@@ -219,14 +208,14 @@ expr_eval (Dwfl_Frame *state, Dwarf_Frame *frame, const Dwarf_Op *ops,
 	    }
 	  break;
 	case DW_OP_regx:
-	  if (! state_get_reg (state, op->number, &val1) || ! push (val1))
+	  if (INTUSE (dwfl_frame_reg) (state, op->number, &val1) != 0 || ! push (val1))
 	    {
 	      free (stack.addrs);
 	      return false;
 	    }
 	  break;
 	case DW_OP_breg0 ... DW_OP_breg31:
-	  if (! state_get_reg (state, op->atom - DW_OP_breg0, &val1))
+	  if (INTUSE (dwfl_frame_reg) (state, op->atom - DW_OP_breg0, &val1) != 0)
 	    {
 	      free (stack.addrs);
 	      return false;
@@ -239,7 +228,7 @@ expr_eval (Dwfl_Frame *state, Dwarf_Frame *frame, const Dwarf_Op *ops,
 	    }
 	  break;
 	case DW_OP_bregx:
-	  if (! state_get_reg (state, op->number, &val1))
+	  if (INTUSE (dwfl_frame_reg) (state, op->number, &val1) != 0)
 	    {
 	      free (stack.addrs);
 	      return false;
@@ -591,7 +580,7 @@ handle_cfi (Dwfl_Frame *state, Dwarf_Addr pc, Dwarf_CFI *cfi, Dwarf_Addr bias)
 	  else if (reg_ops == NULL)
 	    {
 	      /* REGNO is same-value.  */
-	      if (! state_get_reg (state, regno, &regval))
+	      if (INTUSE (dwfl_frame_reg) (state, regno, &regval) != 0)
 		continue;
 	    }
 	  else
@@ -638,9 +627,10 @@ handle_cfi (Dwfl_Frame *state, Dwarf_Addr pc, Dwarf_CFI *cfi, Dwarf_Addr bias)
     }
   if (unwound->pc_state == DWFL_FRAME_STATE_ERROR)
     {
-      if (__libdwfl_frame_reg_get (unwound,
-				   frame->fde->cie->return_address_register,
-				   &unwound->pc))
+      int res = INTUSE (dwfl_frame_reg) (unwound,
+          frame->fde->cie->return_address_register,
+          &unwound->pc);
+      if (res == 0)
 	{
 	  /* PPC32 __libc_start_main properly CFI-unwinds PC as zero.
 	     Currently none of the archs supported for unwinding have
@@ -698,7 +688,7 @@ getfunc (int firstreg, unsigned nregs, Dwarf_Word *regs, void *arg)
   Dwfl_Frame *state = arg;
   assert (firstreg >= 0);
   while (nregs--)
-    if (! __libdwfl_frame_reg_get (state, firstreg++, regs++))
+    if (INTUSE (dwfl_frame_reg) (state, firstreg++, regs++) != 0)
       return false;
   return true;
 }
diff --git a/libdwfl/libdwfl.h b/libdwfl/libdwfl.h
index b323e8fb..edb537c2 100644
--- a/libdwfl/libdwfl.h
+++ b/libdwfl/libdwfl.h
@@ -798,6 +798,12 @@ int dwfl_getthread_frames (Dwfl *dwfl, pid_t tid,
 bool dwfl_frame_pc (Dwfl_Frame *state, Dwarf_Addr *pc, bool *isactivation)
   __nonnull_attribute__ (1, 2);
 
+/* Get the value of the DWARF register number in the given frame.
+   Returns zero on success, -1 on error (invalid DWARF register
+   number) or 1 if the value of the register in the frame is unknown.  */
+int dwfl_frame_reg (Dwfl_Frame *state, unsigned regno, Dwarf_Word *val)
+  __nonnull_attribute__ (1);
+
 /* Return the internal debuginfod-client connection handle for the DWFL session.
    When the client connection has not yet been initialized, it will be done on the
    first call to this function. If elfutils is compiled without support for debuginfod,
diff --git a/libdwfl/libdwflP.h b/libdwfl/libdwflP.h
index 9f598370..a2949e74 100644
--- a/libdwfl/libdwflP.h
+++ b/libdwfl/libdwflP.h
@@ -81,6 +81,7 @@ typedef struct Dwfl_Process Dwfl_Process;
   DWFL_ERROR (LIBEBL_BAD, N_("Internal error due to ebl"))		      \
   DWFL_ERROR (CORE_MISSING, N_("Missing data in core file"))		      \
   DWFL_ERROR (INVALID_REGISTER, N_("Invalid register"))			      \
+  DWFL_ERROR (REGISTER_VAL_UNKNOWN, N_("Unknown register value"))			      \
   DWFL_ERROR (PROCESS_MEMORY_READ, N_("Error reading process memory"))	      \
   DWFL_ERROR (PROCESS_NO_ARCH, N_("Couldn't find architecture of any ELF"))   \
   DWFL_ERROR (PARSE_PROC, N_("Error parsing /proc filesystem"))		      \
@@ -276,9 +277,11 @@ struct Dwfl_Frame
   Dwarf_Addr regs[];
 };
 
-/* Fetch value from Dwfl_Frame->regs indexed by DWARF REGNO.
-   No error code is set if the function returns FALSE.  */
-bool __libdwfl_frame_reg_get (Dwfl_Frame *state, unsigned regno,
+/* Fetch value from Dwfl_Frame->regs indexed by DWARF REGNO.  The
+   function returns 0 on success, -1 on error (invalid DWARF register
+   number), 1 if the value of the register in the frame is unknown.
+   Even on error, no error code is set.  */
+int __libdwfl_frame_reg_get (Dwfl_Frame *state, unsigned regno,
 			      Dwarf_Addr *val)
   internal_function;
 
@@ -786,6 +789,7 @@ INTDECL (dwfl_getthread_frames)
 INTDECL (dwfl_getthreads)
 INTDECL (dwfl_thread_getframes)
 INTDECL (dwfl_frame_pc)
+INTDECL (dwfl_frame_reg)
 INTDECL (dwfl_get_debuginfod_client)
 
 /* Leading arguments standard to callbacks passed a Dwfl_Module.  */
diff --git a/libdwfl/linux-core-attach.c b/libdwfl/linux-core-attach.c
index f68062f0..ee7afa40 100644
--- a/libdwfl/linux-core-attach.c
+++ b/libdwfl/linux-core-attach.c
@@ -257,7 +257,7 @@ core_set_initial_registers (Dwfl_Thread *thread, void *thread_arg_voidp)
 	     FIXME: It depends now on their order in core notes.
 	     FIXME: It uses private function.  */
 	  if (regno < nregs
-	      && __libdwfl_frame_reg_get (thread->unwound, regno, NULL))
+	      && __libdwfl_frame_reg_get (thread->unwound, regno, NULL) == 0)
 	    continue;
 	  Dwarf_Word val;
 	  switch (regloc->bits)
-- 
2.30.2