On 07/01/2014 02:26 AM, Peter Maydell wrote: > On 1 July 2014 09:22, Paolo Bonzini <pbonz...@redhat.com> wrote: >> From: Alexey Kardashevskiy <a...@ozlabs.ru> >> >> The existing test whether "-lm" needs to be included or not is >> insufficient as it reports false negative on Fedora20/ppc64. >> This happens because sin(0.0) is a constant value which compiler >> can safely throw away and therefore there is no need to add "-lm". >> As the result, qemu-nbd/qemu-io/qemu-img tools cannot compile. >> >> This adds a global variable and uses it in the test to prevent >> from optimization. > >> --- a/configure >> +++ b/configure >> @@ -3453,7 +3453,7 @@ fi >> # Do we need libm >> cat > $TMPC << EOF >> #include <math.h> >> -int main(void) { return isnan(sin(0.0)); } >> +double x; int main(void) {return isnan(sin(x));} >> EOF >> if compile_prog "" "" ; then >> : > > This looks to me like we're leaving ourselves open for > a smarter compiler with linktime optimisation to complain > that x is used uninitialized.
If that's your worry, what about: int main(int argc, char **argv) { return isnan(sin(argc > 1)); } -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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