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From: RayeR <glaux AT centrum DOT cz>
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Subject: Re: Using inline asm
Date: Sun, 28 Oct 2007 19:46:23 -0700
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> In the case of gcc, it means "changes in a way that is not known to
> gcc".  GCC will make no assumptions about the contents of the register
> after the asm.

Thanks all for explanation, so if I understand well, the example by
Peter show it right:

>asm("cpuid" : "=a" (eax) : "a" (level)  : "ebx", "ecx", "edx");

The last part of asm block lists the "clobbered" registers which was
changed by CPUID
and we need to tell GCC to restore them automatically - so no push/pop
needed around.
eax is excluded because it is input/output parameter so GCC knows it
was changed because
it had to put the value from a variable to eax.

When I needed some inline asm i looked for examples on the internet
and not all of it
was using the clobber list so it was confusing. I'll have to check my
src if I not
forget it somewhere but I think I was paranoic and used push/pop
instead..