Rene Herman wrote:
On 12-12-07 06:23, 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.
On 32-bit, "=A" is edx:eax. Not sure what the point is in not letting it
be that on 64-bit in fact, but yes, the thing should be compiled as 32-bit.
On 64-bit, "=A" is rdx:rax, which means that a 64-bit value ends up in
rax only (a 128-bit value, which gcc does support on 128-bit platforms,
would be in rdx:rax.)
gcc can't deal internally with values that span partial registers.
-hpa
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