x86: Replace assembly access_ok() with a C variant

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It turns out that the assembly variant doesn't actually produce that
good code, presumably partly because it creates a long dependency
chain with no scheduling, and partly because we cannot get a flags
result out of gcc (which could be fixed with asm goto, but it turns
out not to be worth it.)

The C code allows gcc to schedule and generate multiple (easily
predictable) branches, and as a side benefit we can really optimize
the case where the size is constant.

Link: http://lkml.kernel.org/r/CA%2B55aFzPBdbfKovMT8Edr4SmE2_=%2BOKJFac9XW2awegogTkVTA@mail.gmail.com
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

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Linus Torvalds 2013-12-27 15:30:58 -08:00 • committed by H. Peter Anvin

parent 661c80192d

commit c5fe5d8068

1 changed files with 17 additions and 11 deletions

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arch/x86/include/asm/uaccess.h

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