Re: [PATCH x86_64] Optimize access to globals in "-fpie -pie" builds with copy relocations

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Feb 04, 2015 at 10:27:34AM -0800, Sriraman Tallam wrote:
> On Tue, Feb 3, 2015 at 5:16 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> > On Tue, Feb 3, 2015 at 2:19 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> >> On Tue, Feb 03, 2015 at 02:03:14PM -0800, H.J. Lu wrote:
> >>> So we aren't SYMBOL_REF_EXTERNAL_P nor
> >>> SYMBOL_REF_LOCAL_P.  What do we reference?
> >>
> >> That is reasonable.  There is no guarantee the extern weak symbol is local,
> >> it could very well be non-local.  All that you know about the symbols is
> >> that its address is non-NULL in that case.
> >>
> >
> > This may be true for shared library.  But it isn't true for PIE:
> 
> 
> Also, gcc and g++ are inconsistent about something even more simple:
> 
> $ cat x.c
> 
> int a;
> 
> int main() {
>   printf("%d\n", a);
> }
> 
> With gcc -fPIE x.c
> SYMBOL_REF_LOCAL_P(op0) = false
> 
> With g++ -fPIE x.c
> SYMBOL_REF_LOCAL_P(op0) = true

Try -fno-common for C and you'll get the same result as in C++.
Common symbols can't be considered SYMBOL_REF_LOCAL_P, they might resolve
to a non-common symbol from different TU.

	Jakub