[PATCH 2/5] elf: Avoid unnecessary slowdown from profiling with audit (BZ#15533)

[Florian Weimer]

* Adhemerval Zanella via Libc-alpha:

> diff --git a/elf/dl-reloc.c b/elf/dl-reloc.c
> index e13a672ade..998cfef099 100644
> --- a/elf/dl-reloc.c
> +++ b/elf/dl-reloc.c
> @@ -181,7 +181,18 @@ _dl_relocate_object (struct link_map *l, struct r_scope_elem *scope[],
>  #ifdef SHARED
>    /* If we are auditing, install the same handlers we need for profiling.  */
>    if ((reloc_mode & __RTLD_AUDIT) == 0)
> -    consider_profiling |= GLRO(dl_audit) != NULL;
> +    {
> +      struct audit_ifaces *afct = GLRO(dl_audit);
> +      for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
> +	{
> +	  /* Profiling is needed only if PLT hooks are provided.  */
> +	  if (afct->symbind != NULL
> +	      || afct->ARCH_LA_PLTENTER != NULL
> +	      || afct->ARCH_LA_PLTEXIT != NULL)
> +	    consider_profiling = 1;
> +	  afct = afct->next;
> +	}
> +    }

Is the afct->symbind check really necessary?  Looking at _dl_fixup, it
should be safe to call symbind with just the standard trampoline.

I think this needs a NEWS entry, describing how to activate this
optimization.

Thanks,
Florian