On Thu, Jan 14, 2016 at 5:39 AM, Richard W.M. Jones <rjo...@redhat.com>
wrote:
> On Wed, Jan 13, 2016 at 10:00:08PM -0700, Dave Johansen wrote:
> > I was working on packaging rr [1] and one of the tests [2] fails to build
> > when optimizations are turned on. I've reduced it to the following and
> > still been able to reproduce the issue:
> >
> > static const float xmm0 = 10;
> >
> > int main() {
> > __asm__ __volatile__(
> > #if __i386__
> > "movss xmm0, %xmm0\n\t"
> > #elif __x86_64__
> > "movss xmm0(%rip), %xmm0\n\t"
> > #else
> > #error unexpected architecture
> > #endif
> > );
> >
> > return 0;
> > }
> >
> > Here's the output on F23 x86_64:
> > $ gcc fxregs.c -O0
> > $ gcc fxregs.c -O1
> > /tmp/cccdze3O.o: In function `main':
> > fxregs.c:(.text+0x4): undefined reference to `xmm0'
> > collect2: error: ld returned 1 exit status
> >
> > Is this a gcc bug or is there something that I need to do in the build to
> > get the tests to build without error?
>
> I think it's a bug in your test. GCC is just optimizing away the xmm0
> variable because it cannot see "inside" the asm to know that it is
> being used.
>
Yes, it appears that you're right. Removing the static fixes the
compilation issue when optimizations are enabled. I'll submit a patch
upstream.
Thanks,
Dave
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