Kyle McMartin wrote:
On Wed, Dec 12, 2007 at 12:31:18AM +0100, Rene Herman wrote:
asm volatile ("rdtsc": "=A" (tsc));
rdtsc returns a 64-bit value in two 32-bit regs, you need to do
inline unsigned long long rdtsc(void)
{
unsigned int lo, hi;
asm volatile ("rdtsc": "=a" (lo), "=d" (hi));
return (unsigned long long)hi << 32 | lo;
}
as in msr.h, otherwise you'll only be looking at the value in %rax.
"=A" works on 32-bit systems (only), obviously, and gcc will generally
produce slightly better code as a result (gcc could really use a
register renaming/copy propagation step *after* multi-register entities
are broken apart, at least on architectures which don't have register
pairs as a hardware constraint.)
-hpa
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