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

[Linus Torvalds <torvalds@osdl.org>]

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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