Re: copy to suer space

["H. Peter Anvin" <hpa@zytor.com>]

Followup to:  <200111231440.fANEeh213167@criticalsoftware.com>
By author:    =?iso-8859-1?q?Lu=EDs=20Henriques?= 
	<lhenriques@criticalsoftware.com>
In newsgroup: linux.dev.kernel
> 
> When I read the timestamp («rdtsc»), a value is returned to edx:eax. This 
> code works just fine when I put it in the process stack. The problem is when 
> I want to compare %edx instead of %eax, that is:
> 
> 	rdtsc
> 	movl %edx, %ecx
> 	addl $0x1, %ecx
>    loop:
> 	rdtsc
> 	cmp %ecx, %edx
> 	jb loop
> 
> This is supposed to take much more time than the other loop. When I write 
> this code to the stack of my process, a segmentation fault occurs after some 
> time. Why? I'm not changing the stack at any moment! (By the way, the stack 
> pointer is pointing to the end of my code...)
> 

Did you remember to restore all the registers, including %eax and
%eflags, before you return?

	-hpa
-- 
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