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From: "vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug gdb/27891] maintenance selftest fail when an executable is loaded
Date: Mon, 13 Sep 2021 10:32:12 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D27891

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |alahay01 at gcc dot gnu.or=
g,
                   |                            |luis.machado at linaro dot=
 org,
                   |                            |vries at gcc dot gnu.org

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Andrew Burgess from comment #0)
>  Self test failed: arch armv8.1-m.main: self-test failed at
> ../../src/gdb/disasm-selftests.c:165

The first error I run into is this one, and I've debugged it.

1. With exec.

In gdb_print_insn_arm, we run into this and set info->flags |=3D
USER_SPECIFIED_MACHINE_TYPE:
...
  /* GDB is able to get bfd_mach from the exe_bfd, info->mach is=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20
     accurate, so mark USER_SPECIFIED_MACHINE_TYPE bit.  Otherwise,=20=20=
=20=20=20=20=20=20=20=20=20=20=20
     opcodes/arm-dis.c:print_insn reset info->mach, and it will trigger=20=
=20=20=20=20=20=20=20=20
     the assert on the mismatch of info->mach and=20=20=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
     bfd_get_mach (current_program_space->exec_bfd ()) in=20=20=20=20=20=20=
=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20=20
     default_print_insn.  */
  if (current_program_space->exec_bfd () !=3D NULL)
    info->flags |=3D USER_SPECIFIED_MACHINE_TYPE;
...
and consequently we don't do this in print_insn:
...
      if ((info->flags & USER_SPECIFIED_MACHINE_TYPE) =3D=3D 0)
          info->mach =3D bfd_mach_arm_unknown;
...
so we end up doing this in select_arm_features:
...
    case bfd_mach_arm_8_1M_MAIN:
      ARM_SET_FEATURES (ARM_ARCH_V8_1M_MAIN);
      arm_feature_set mve_all
        =3D ARM_FEATURE_CORE_HIGH (ARM_EXT2_MVE | ARM_EXT2_MVE_FP);
      ARM_MERGE_FEATURE_SETS (arch_fset, arch_fset, mve_all);
      force_thumb =3D 1;
      break;
...

With force_thumb set, we disassemble only two bytes, and the selftest fails.

2. Without exec.

- in gdb_print_insn_arm, we don't set
  info->flags |=3D USER_SPECIFIED_MACHINE_TYPE.
- in print_insn, we do bfd_mach_arm_unknown
- in select_arm_features, we don't set force_thumb

Without force_thumb set, we disassemble four bytes, and the selftest passes.

--=20
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