Date: Wed, 30 Oct 2013 10:04:12 +0000 From: Bruce Cran <bruce@cran.org.uk> To: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Code segfaults with clang -O1, works with gcc49 and clang -O2 Message-ID: <5270D99C.6070901@cran.org.uk>
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The following code works (on FreeBSD 11-CURRENT) with gcc49 or clang -O2
or higher, but segfaults in do_cpuid() with clang -O1 or lower. Is there
a bug in the asm statement, or is clang doing something wrong?
#include <stdio.h>
static inline void do_cpuid(unsigned int *eax, unsigned int *ebx,
unsigned int *ecx, unsigned int *edx)
{
asm volatile("cpuid"
: "=a" (*eax), "=b" (*ebx), "=r" (*ecx), "=d" (*edx)
: "0" (*eax), "2" (*ecx)
: "memory");
}
int main(int argc, char **argv)
{
unsigned int a = 0, b = 0, c = 0, d = 0;
do_cpuid(&a, &b, &c, &d);
printf("%d %d %d %d\n", a, b, c, d);
return 0;
}
--
Bruce Cran
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