Re: [PATCH] Fix prefetch patching in 2.5-bk

From: Linus Torvalds (torvalds@transmeta.com)
Date: Wed Apr 30 2003 - 20:21:52 EST


On Thu, 1 May 2003, Andi Kleen wrote:
>
> If your machine BUG()s in apply_alternatives at booting
> or module loading you need this patch.

I applied it, but I don't have to like it..

How about doing this differently, and having something like this:

        #define nop_alternative(newinstr, feature) \
                ".section .altinstructions,\"a\"\n" \
                " .align 4\n"
                " .long 660f\n"
                " .long 663f\n"
                " .byte %c0\n"
                " .byte 0\n"
                " .byte 664f-663f\n"
                ".previous\n"
                ".section .altinstr_replacement",\"ax\"\n"
                "663:\n\t" newinstr "\n664:\n"
                ".previous"
                "660:\n\t"
                ".rept 664b-663b, 0x90\n\t"

and making "sourcelen==0" a special case for replacement (replace with the
proper destination length nop, instead of having that "0x90 0x90 0x90"
sequence).

This allows you to use arbitrary-sized things without having to worry
about having to have the size right, or without having to use
unnecessarily long nop-sequences. You'll always get the right-size nop.

                Linus

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