[PATCH] [gdb/tdep] Don't use i386 unwinder for amd64

[Tom de Vries <tdevries@suse.de>]

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
...

ISTM me there's no reason for the i386 unwinders to be there for amd64.

Furthermore, there's a generic need to play around with enabling and disabling
unwinders, see PR8434.  Currently, that's only available for both the
dwarf2 unwinders at once using "maint set dwarf unwinders on/off".

If I manually disable the "amd64 epilogue" unwinder, the "i386 epilogue"
unwinder becomes active and gives the wrong answer, while I'm actually
interested in the result of the dwarf2 unwinder.  Of course I can also
manually disable the "i386 epilogue", but I take the fact that I have to do
that as evidence that on amd64, the "i386 epilogue" is not only unnecessary,
but in the way.

Fix this by only adding the i386 unwinders only if
"info.bfd_arch_info->bits_per_word == 32".

Note that for the x32 abi (x86_64/-mx32) the unwinder list is the same as for
amd64 (x86_64/-m64), without and with this commit.

Tested on x86_64-linux, -m64 and -m32.  Not tested with -mx32.

PR tdep/30102
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30102
---
 gdb/i386-tdep.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

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 *arches)
      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 *arches)
     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.  */

base-commit: be01687991aa6c8517b3e635b8f13b0bac6a851a
-- 
2.35.3