[PINGv2][PATCH] gdb/testsuite: change hardcoded assembly in gdb.arch/disp-step-insn-reloc.exp

[Bruno Larsen <blarsen@redhat.com>]

Ping!

-- 
Cheers,
Bruno

On 26/04/2023 15:29, Bruno Larsen wrote:
> When testing gdb.arch.disp-step-insn-reloc.exp with clang in an x86_64
> machine, the compiled test case would segfault when returning from
> the function can_relocate_call, with a suggestion of a broken stack.
> The example assembly in the commment was the following:
>
>     f:
>       MOV $1, %[ok]
>       JMP end
>     set_point0:
>       CALL f ; tracepoint here.
>     end:
>
> And the segmentation fault happening at the final "ret" instruction of
> the original function.  This suggests that gcc's compilation process would
> realize that no ret instruction ever happened after that call and doesn't
> save the return address, while clang's process wouldn't.  Looking at the
> generated instructions, we can indeed see a difference:
>
> clang's version: e8 f1 ff ff ff          call   11a4 <can_relocate_call+0x14>
> gcc's version:   e8 f4 ff ff ff          call   401125 <can_relocate_call+0x11>
>
> Notice the difference on the second byte.
>
> Changing the assembly to use "ret" instead of "JMP end" does not change
> the behavior of the program and guarantees a compiler independent
> behavior.  This commit does just that.
> ---
>   gdb/testsuite/gdb.arch/insn-reloc.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/gdb/testsuite/gdb.arch/insn-reloc.c b/gdb/testsuite/gdb.arch/insn-reloc.c
> index f687c2c5631..365e6180057 100644
> --- a/gdb/testsuite/gdb.arch/insn-reloc.c
> +++ b/gdb/testsuite/gdb.arch/insn-reloc.c
> @@ -49,10 +49,9 @@ fail (void)
>        JMP set_point0
>      f:
>        MOV $1, %[ok]
> -     JMP end
> +     RET
>      set_point0:
>        CALL f ; tracepoint here.
> -   end:
>   
>      */
>   
> @@ -65,10 +64,9 @@ can_relocate_call (void)
>          "  jmp " SYMBOL (set_point0) "\n"
>          "0:\n"
>          "  mov $1, %[ok]\n"
> -       "  jmp 1f\n"
> +       "  ret\n"
>          SYMBOL (set_point0) ":\n"
>          "  call 0b\n"
> -       "1:\n"
>          : [ok] "=r" (ok));
>   
>     if (ok == 1)