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SubjectRe: [PATCH 1/10] Cr4 is valid on some 486s


On Fri, 11 Nov 2005, Zachary Amsden wrote:
>
> Agree nested exceptions are evil. But where is this called from execption
> context?

We have really nice ways of handling these things, so we should just use
them.

For example, you can do

static inline void read_cr4(void)
{
unsigned long cr4;
alternative_input("xorl %0,%0",
"movl %%cr4,%0",
X86_FEATURE_CR4,
"r" (cr4));
return cr4;
}
and then just add that feature-flag discovery early on in boot (it needs
to be pretty early, since the alternative instruction rewriting happens
early).

We have several "calculated" features already. Things like X86_FEATURE_P4
etc.

Linus
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