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* [Bug tdep/30102] New: [gdb/tdep, amd64] Disable i386 unwinders
@ 2023-02-09 14:24 vries at gcc dot gnu.org
  2023-02-09 15:21 ` [Bug tdep/30102] " vries at gcc dot gnu.org
                   ` (4 more replies)
  0 siblings, 5 replies; 6+ messages in thread
From: vries at gcc dot gnu.org @ 2023-02-09 14:24 UTC (permalink / raw)
  To: gdb-prs

https://sourceware.org/bugzilla/show_bug.cgi?id=30102

            Bug ID: 30102
           Summary: [gdb/tdep, amd64] Disable i386 unwinders
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: minor
          Priority: P2
         Component: tdep
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

As mentioned here (
https://sourceware.org/pipermail/gdb-patches/2023-February/196724.html ), for
i386 we have these unwinders:
...
$ gdb -q -batch -ex "set arch i386" -ex "maint info frame-unwinders"
The target architecture is set to "i386".
dummy                   DUMMY_FRAME
dwarf2 tailcall         TAILCALL_FRAME
inline                  INLINE_FRAME
i386 epilogue           NORMAL_FRAME
dwarf2                  NORMAL_FRAME
dwarf2 signal           SIGTRAMP_FRAME
i386 stack tramp        NORMAL_FRAME
i386 sigtramp           SIGTRAMP_FRAME
i386 prologue           NORMAL_FRAME
...
and for amd64:
...
$ gdb -q -batch -ex "set arch i386:x86-64" -ex "maint info frame-unwinders"
The target architecture is set to "i386:x86-64".
dummy                   DUMMY_FRAME
dwarf2 tailcall         TAILCALL_FRAME
inline                  INLINE_FRAME
python                  NORMAL_FRAME
amd64 epilogue          NORMAL_FRAME
i386 epilogue           NORMAL_FRAME
dwarf2                  NORMAL_FRAME
dwarf2 signal           SIGTRAMP_FRAME
amd64 sigtramp          SIGTRAMP_FRAME
amd64 prologue          NORMAL_FRAME
i386 stack tramp        NORMAL_FRAME
i386 sigtramp           SIGTRAMP_FRAME
i386 prologue           NORMAL_FRAME
...

So, why are the i386 unwinders there for amd64?

I recently played around with disabling or moving the "amd64 epilogue"
unwinder, and while investigating the effect of that, I came across a failure
that was due to the "i386 epilogue" unwinder becoming active and giving the
wrong answer, which suggest that the i386 unwinders shouldn't be there for
amd64.

Using this tentative patch:
...
diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c
index 580664d2ce5..8dccae633f7 100644
--- a/gdb/i386-tdep.c
+++ b/gdb/i386-tdep.c
@@ -8613,7 +8613,8 @@ i386_gdbarch_init (struct gdbarch_info info, struct
gdbarch_list *arc
hes)
      appended to the list first, so that it supercedes the DWARF
      unwinder in function epilogues (where the DWARF unwinder
      currently fails).  */
-  frame_unwind_append_unwinder (gdbarch, &i386_epilogue_frame_unwind);
+  if (info.bfd_arch_info->bits_per_word == 32)
+    frame_unwind_append_unwinder (gdbarch, &i386_epilogue_frame_unwind);

   /* Hook in the DWARF CFI frame unwinder.  This unwinder is appended
      to the list before the prologue-based unwinders, so that DWARF
@@ -8792,9 +8793,12 @@ i386_gdbarch_init (struct gdbarch_info info, struct
gdbarch_list *ar
ches)
     tdep-> bnd0_regnum = -1;

   /* Hook in the legacy prologue-based unwinders last (fallback).  */
-  frame_unwind_append_unwinder (gdbarch, &i386_stack_tramp_frame_unwind);
-  frame_unwind_append_unwinder (gdbarch, &i386_sigtramp_frame_unwind);
-  frame_unwind_append_unwinder (gdbarch, &i386_frame_unwind);
+  if (info.bfd_arch_info->bits_per_word == 32)
+    {
+      frame_unwind_append_unwinder (gdbarch, &i386_stack_tramp_frame_unwind);
+      frame_unwind_append_unwinder (gdbarch, &i386_sigtramp_frame_unwind);
+      frame_unwind_append_unwinder (gdbarch, &i386_frame_unwind);
+    }

   /* If we have a register mapping, enable the generic core file
      support, unless it has already been enabled.  */
...
we have for i386 as before, and for amd64:
...
$ gdb -q -batch -ex "set arch i386:x86-64" -ex "maint info frame-unwinders"
The target architecture is set to "i386:x86-64".
dummy                   DUMMY_FRAME     
dwarf2 tailcall         TAILCALL_FRAME  
inline                  INLINE_FRAME    
python                  NORMAL_FRAME    
amd64 epilogue          NORMAL_FRAME    
dwarf2                  NORMAL_FRAME    
dwarf2 signal           SIGTRAMP_FRAME  
amd64 sigtramp          SIGTRAMP_FRAME  
amd64 prologue          NORMAL_FRAME    
...

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^ permalink raw reply	[flat|nested] 6+ messages in thread
end of thread, other threads:[~2023-02-11  8:05 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-02-09 14:24 [Bug tdep/30102] New: [gdb/tdep, amd64] Disable i386 unwinders vries at gcc dot gnu.org
2023-02-09 15:21 ` [Bug tdep/30102] " vries at gcc dot gnu.org
2023-02-09 22:02 ` vries at gcc dot gnu.org
2023-02-10 12:56 ` vries at gcc dot gnu.org
2023-02-11  8:04 ` cvs-commit at gcc dot gnu.org
2023-02-11  8:05 ` vries at gcc dot gnu.org

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