On Thu, Jan 14, 2016 at 5:39 AM, Richard W.M. Jones <rjones@xxxxxxxxxx> 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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