Re: [PATCH][gdb/symtab] Fix gdb.base/vla-optimized-out.exp with clang

[Gary Benson via Gdb-patches <gdb-patches@sourceware.org>]

Gary Benson wrote:
> Thank you for picking this up Tom (de Vries).  Your patch looks good,
> however I wanted to point out that the location expressions Clang
> generates for gdb.base/vla-ptr.exp don't end with DW_OP_stack_value:
> 
>   < 2><0x000000a3>  DW_TAG_variable
>                       DW_AT_location    len 0x0002: 9168: DW_OP_fbreg -24
>                       DW_AT_name      __vla_expr0
>                       DW_AT_type      <0x00000118>
>                       DW_AT_artificial        yes(1)
>   < 2><0x000000af>  DW_TAG_variable
>                       DW_AT_location  len 0x0002: 9160: DW_OP_fbreg -32
>                       DW_AT_name      __vla_expr1
>                       DW_AT_type      <0x00000118>
>                       DW_AT_artificial        yes(1)
> 
> It wasn't obvious to me how GDB with your patch would handle these.
> Did you check your patch using that test?

I forgot to add, that I did, and the final test failed with my setup:

  gdb.base/vla-ptr.exp
  ...
  print td_vla
  GCC compiled:       $6 = {4, 5, 6, 7, 8}
  Clang-12 compiled:  $6 = 0x7fffffffc0d0

But!  This is potentially a different issue.  I don't think that test
accesses the array's size, and I've definitely seen typedef-related
failures with Clang compared with GCC.

(I don't need you to debug this for me, I'm just making sure you're
aware!)

Thanks,
Gary

-- 
Gary Benson - he / him / his
Principal Software Engineer, Red Hat