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

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

[Tom de Vries]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=af0d0f34d8bf7482e598308b54e7ba0ae9b0c349

commit af0d0f34d8bf7482e598308b54e7ba0ae9b0c349
Author: Tom de Vries <tdevries@suse.de>
Date:   Sat Feb 11 09:04:51 2023 +0100

    [gdb/tdep] Don't use i386 unwinder for amd64
    
    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 if
    "info.bfd_arch_info->bits_per_word == 32".
    
    Note that the x32 abi (x86_64/-mx32):
    - has the same unwinder list as amd64 (x86_64/-m64) before this commit,
    - has info.bfd_arch_info->bits_per_word == 64, the same as amd64, and
      consequently,
    - has the same unwinder list as amd64 after this commit.
    
    Tested on x86_64-linux, -m64 and -m32.  Not tested with -mx32.
    
    Reviewed-By: John Baldwin <jhb@freebsd.org>
    
    PR tdep/30102
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30102

Diff:
---
 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.  */