On 20.01.2010, at 07:48, Stephen Rothwell wrote:
> [Not sure what happened to the previous versions To/CC lists, sorry]
>
> Hi all,
>
> Today's linux-next build (powerpc allyesconfig) produced this warning:
>
> arch/powerpc/kvm/book3s.c: In function '__kvmppc_vcpu_run':
> arch/powerpc/kvm/book3s.c:1102: warning: 'ext_bkp.vrsave' may be used
> uninitialized in this function
>
> Introduced by commit 2609c1d06b6a7952273fb33b33ad32aff0628146 ("KVM: PPC:
> Add support for FPU/Altivec/VSX"). This *may* be a false positive but
> will be a problem for normal builds where warnings are treated as errors
> in arch/powerpc.
This is odd. The same function saves and restores ext_bkp.vrsave under a common
condition:
if (save_vec) {
if (current->thread.regs->msr & MSR_VEC)
giveup_altivec(current);
memcpy(ext_bkp.vr, current->thread.vr, sizeof(ext_bkp.vr));
ext_bkp.vscr = current->thread.vscr;
ext_bkp.vrsave = current->thread.vrsave;
}
[...]
if (save_vec && current->thread.used_vr) {
memcpy(current->thread.vr, ext_bkp.vr, sizeof(ext_bkp.vr));
current->thread.vscr = ext_bkp.vscr;
current->thread.vrsave = ext_bkp.vrsave;
}
So there can't be a case where ext_bkp.vrsave is read, but not written to
before, which is what this warning implies, right?
Also, why doesn't gcc complain about vscr too then? They're both used in the
very same if statement.
Additionally, while compiling locally I looked for warnings and didn't spot
any. So apparently our compiler versions / options don't match. Which version
of gcc are you using? I assume a gcc bug.
$ gcc --version
gcc (SUSE Linux) 4.3.2 [gcc-4_3-branch revision 141291]
Alex
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