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

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

Marcin Kościelnicki wrote:
> On 29/03/16 20:18, Ulrich Weigand wrote:
> > 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.
> 
> Right.  I've tested on i386 and x86_64.  Unfortunately I have no means 
> of testing on aarch64 - could someone lend a hand here?

Pierre or Yao ... you've been working in this area recently, could you
have a look at Marcin's patch and give it a test?   Thanks!

> Also, since s390 tracepoints have just landed, I'll update the patch to 
> cover s390 and s390x as well.
> >
> >> +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?
> 
> Whoops, you're obviously right - I'm going to change the guard to 
> #ifndef HAVE_GETAUXVAL (since it's already inside #ifdef 
> IN_PROCESS_AGENT).  I'll send this fix in v3 along with s390 support.

OK, thanks!

Bye,
Ulrich

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