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| author | H. Peter Anvin <hpa@zytor.com> | 2013-12-28 01:52:47 +0100 |
|---|---|---|
| committer | H. Peter Anvin <hpa@zytor.com> | 2013-12-28 02:02:53 +0100 |
| commit | a740576a4abf933de8f50787f24f24456cebd761 (patch) | |
| tree | e46ad30a727de5f0b8d91b381f1c67f05ebfb260 /Documentation/tpm | |
| parent | x86: Replace assembly access_ok() with a C variant (diff) | |
| download | linux-a740576a4abf933de8f50787f24f24456cebd761.tar.xz linux-a740576a4abf933de8f50787f24f24456cebd761.zip | |
x86: Slightly tweak the access_ok() C variant for better code
gcc can under very specific circumstances realize that the code
sequence:
foo += bar;
if (foo < bar) ...
... is equivalent to a carry out from the addition. Tweak the
implementation of access_ok() (specifically __chk_range_not_ok()) to
make it more likely that gcc will make that connection. It isn't
fool-proof (sometimes gcc seems to think it can make better code with
lea, and ends up with a second comparison), still, but it seems to be
able to connect the two more frequently this way.
Cc: Linus Torvalds <torvalds@linux-foundation.org>
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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