Re: [rtl] Problems with RDTSC examples posted here recently

[Der Herr Hofrat <der.herr@hofr.at>]

> > On Thu, Nov 01, 2001 at 02:54:37PM -0700, John Regehr wrote:
> > > > Don't forget to make sure it's __volatile__, elsewise this is the very
> > > > epitome of what would produce dodgy results...
> > > 
> > > Right.  So method2 and method2A seem to be broken in multiple ways -
> > > forget you ever saw them.  Rather, look at this page:
> 
> in what way is method2 brocken ??
> 
> if you compile method1 and method2A and look at the assembler coee they are
> absolutly the same - the only difference on the source level is that its easier
> to read "mov" than "0x31" thats all.
> 
> ---method1---
> __inline__ unsigned long long int rdtsc(void)
> {
> 	unsigned long long int x;
> 	__asm__ volatile (".byte 0x0f, 0x31" : "=A" (x));
> 	return x;
> }
> 
> 
> ---method2A---
> __inline__ unsigned long long int hwtime(void)
> {
> 	unsigned long long int x;
> 	__asm__("rdtsc\n\t"
> 		"mov %%edx, %%ecx\n\t"
> 		:"=A" (x));
> 	return x;
> }
>

forgot to put in objdump output in the last post


08048430 <rdtsc>:
 8048430:	55                   	push   %ebp
 8048431:	89 e5                	mov    %esp,%ebp
 8048433:	83 ec 14             	sub    $0x14,%esp
 8048436:	53                   	push   %ebx
 8048437:	0f 31                	rdtsc  
 8048439:	89 c1                	mov    %eax,%ecx
 804843b:	89 d3                	mov    %edx,%ebx
 804843d:	89 4d f8             	mov    %ecx,0xfffffff8(%ebp)
 8048440:	89 5d fc             	mov    %ebx,0xfffffffc(%ebp)
 8048443:	8b 4d f8             	mov    0xfffffff8(%ebp),%ecx
 8048446:	8b 5d fc             	mov    0xfffffffc(%ebp),%ebx
 8048449:	89 c8                	mov    %ecx,%eax
 804844b:	89 da                	mov    %ebx,%edx
 804844d:	eb 01                	jmp    8048450 <rdtsc+0x20>
 804844f:	90                   	nop    
 8048450:	8b 5d e8             	mov    0xffffffe8(%ebp),%ebx
 8048453:	89 ec                	mov    %ebp,%esp
 8048455:	5d                   	pop    %ebp
 8048456:	c3                   	ret    
 8048457:	89 f6                	mov    %esi,%esi
 8048459:	8d bc 27 00 00 00 00 	lea    0x0(%edi,1),%edi

08048460 <hwtime>:
 8048460:	55                   	push   %ebp
 8048461:	89 e5                	mov    %esp,%ebp
 8048463:	83 ec 14             	sub    $0x14,%esp
 8048466:	53                   	push   %ebx
 8048467:	0f 31                	rdtsc  
 8048469:	89 d1                	mov    %edx,%ecx
 804846b:	89 c1                	mov    %eax,%ecx
 804846d:	89 d3                	mov    %edx,%ebx
 804846f:	89 4d f8             	mov    %ecx,0xfffffff8(%ebp)
 8048472:	89 5d fc             	mov    %ebx,0xfffffffc(%ebp)
 8048475:	8b 4d f8             	mov    0xfffffff8(%ebp),%ecx
 8048478:	8b 5d fc             	mov    0xfffffffc(%ebp),%ebx
 804847b:	89 c8                	mov    %ecx,%eax
 804847d:	89 da                	mov    %ebx,%edx
 804847f:	eb 00                	jmp    8048481 <hwtime+0x21>
 8048481:	8b 5d e8             	mov    0xffffffe8(%ebp),%ebx
 8048484:	89 ec                	mov    %ebp,%esp
 8048486:	5d                   	pop    %ebp
 8048487:	c3                   	ret    
 8048488:	90                   	nop    
 8048489:	8d b4 26 00 00 00 00 	lea    0x0(%esi,1),%esi