Re: [PATCH 4/4] libgcc: Use _dl_find_eh_frame in _Unwind_Find_FDE

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Nov 03, 2021 at 05:28:55PM +0100, Florian Weimer wrote:
> --- a/libgcc/unwind-dw2-fde-dip.c
> +++ b/libgcc/unwind-dw2-fde-dip.c
> @@ -129,6 +129,30 @@ unw_eh_callback_data_dbase (const struct unw_eh_callback_data *data
>  #endif
>  }
>  
> +#ifdef DL_FIND_EH_FRAME_DBASE
> +#if DL_FIND_EH_FRAME_DBASE != NEED_DBASE_MEMBER
> +#error "DL_FIND_EH_FRAME_DBASE != NEED_DBASE_MEMBER"

Instead of #error just don't define USE_DL_FIND_EH_FRAME?
I.e.
#ifdef DL_FIND_EH_FRAME_DBASE
#if DL_FIND_EH_FRAME_DBASE == NEED_DBASE_MEMBER
> +#define USE_DL_FIND_EH_FRAME 1
> +#define DL_FIND_EH_FRAME_CONDITION 1
> +#endif
?
Is it a good idea to have different arguments of the function for
i386/nios2/frv/bfind vs. the rest, wouldn't just always passing void **__dbase
argument be cleaner?
Internally it is fine to differentiate based on NEED_DBASE_MEMBER, but doing
that on a public interface?

> +/* Fallback declaration for old glibc headers.  DL_FIND_EH_FRAME_DBASE is used
> +   as a proxy to determine if <dlfcn.h> declares _dl_find_eh_frame.  */
> +#if defined __GLIBC__ && !defined DL_FIND_EH_FRAME_DBASE
> +#if NEED_DBASE_MEMBER
> +void *_dl_find_eh_frame (void *__pc, void **__dbase) __attribute__ ((weak));
> +#else
> +void *_dl_find_eh_frame (void *__pc) __attribute__ ((weak));
> +#endif
> +#define USE_DL_FIND_EH_FRAME 1
> +#define DL_FIND_EH_FRAME_CONDITION (_dl_find_eh_frame != NULL)
> +#endif

I'd prefer not to do this.  If we find glibc with the support in the
headers, let's use it, otherwise let's keep using what we were doing before.

> +#if NEED_DBASE_MEMBER
> +      eh_frame = _dl_find_eh_frame (pc, &dbase);
> +#else
> +      dbase = NULL;
> +      eh_frame = _dl_find_eh_frame (pc);
> +#endif
> +      if (eh_frame == NULL)
> +	return NULL;
> +
> +      struct find_fde_tail_result result
> +	= find_fde_tail ((_Unwind_Ptr) pc, eh_frame, (_Unwind_Ptr) dbase);
> +      if (result.entry != NULL)
> +	{
> +	  bases->tbase = NULL;
> +	  bases->dbase = (void *) dbase;
> +	  bases->func = result.func;
> +	}
> +      return result.entry;
> +    }
> +#endif
> +
>    data.pc = (_Unwind_Ptr) pc;
>  #if NEED_DBASE_MEMBER
>    data.dbase = NULL;
> -- 
> 2.31.1

Otherwise LGTM.

	Jakub