Re: [PATCH 2/4 v2] IPA: Add alloc_jump_pad_buffer target hook.

["Ulrich Weigand" <uweigand@de.ibm.com>]

Marcin Kościelnicki wrote:

> Targets may have various requirements on the required location of the jump
> pad area.  Currently IPA allocates it at the lowest possible address,
> so that it is reachable by branches from the executable.  However, this
> fails on powerpc, which has executable link address (0x10000000) much
> larger than branch reach (+/- 32MiB).
> 
> This makes jump pad buffer allocation a target hook instead.  The current
> implementations are as follows:
> 
> - i386: Branches can reach anywhere, so just mmap it.  This avoids
>   the linear search dance.
> - x86_64: Branches have +/-2GiB of reach, and executable is loaded low,
>   so just call mmap with MAP_32BIT.  Likewise avoids the linear search.
> - aarch64: Branches have +-128MiB of reach, executable loaded at 4MiB.
>   Do a linear search from 4MiB-size downwards to page_size.

This makes sense to me, but I agree that this needs testing on the
affected platforms, in particular aarch64.

> +void *alloc_jump_pad_buffer (size_t size);
> +#ifdef HAVE_GETAUXVAL
> +unsigned long getauxval (unsigned long type);
> +#endif

Shouldn't this use a guard like
#if !defined HAVE_GETAUXVAL && defined IN_PROCESS_AGENT
just as in the source file?

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU/Linux compilers and toolchain
  Ulrich.Weigand@de.ibm.com