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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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