diff options
| 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 | |
| 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>
| -rw-r--r-- | arch/x86/include/asm/uaccess.h | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 84ecf1df2ac6..6f1bb74d547b 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -41,7 +41,7 @@ * Test whether a block of memory is a valid user space address. * Returns 0 if the range is valid, nonzero otherwise. */ -static inline int __chk_range_not_ok(unsigned long addr, unsigned long size, unsigned long limit) +static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, unsigned long limit) { /* * If we have used "sizeof()" for the size, @@ -55,7 +55,9 @@ static inline int __chk_range_not_ok(unsigned long addr, unsigned long size, uns /* Arbitrary sizes? Be careful about overflow */ addr += size; - return (addr < size) || (addr > limit); + if (addr < size) + return true; + return addr > limit; } #define __range_not_ok(addr, size, limit) \ @@ -84,7 +86,7 @@ static inline int __chk_range_not_ok(unsigned long addr, unsigned long size, uns * this function, memory access functions may still return -EFAULT. */ #define access_ok(type, addr, size) \ - (likely(__range_not_ok(addr, size, user_addr_max()) == 0)) + likely(!__range_not_ok(addr, size, user_addr_max())) /* * The exception table consists of pairs of addresses relative to the |