Re: [RFT] Port 0x80 I/O speed

[H. Peter Anvin]

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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