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overflow-arith: begin to add support for overflow builtin functions

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The idea of the overflow-arith.h header is to collect overflow checking
functions in one central place.

If gcc compiler supports the __builtin_overflow_* builtins we use them
because they might give better performance, otherwise the code falls
back to normal overflow checking functions.

The builtin_overflow functions are supported by gcc-5 and clang. The
matter of supporting clang is to just provide a corresponding
CC_HAVE_BUILTIN_OVERFLOW, because the specific overflow checking builtins
don't differ between gcc and clang.

I just provide overflow_usub function here as I intend this to get merged
into net, more functions will definitely follow as they are needed.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Hannes Frederic Sowa 2015-10-16 11:32:42 +02:00 committed by David S. Miller
parent c80dbe0461
commit 79907146fb
2 changed files with 22 additions and 0 deletions
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4
include/linux/compiler-gcc.h
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@ -237,6 +237,10 @@
#define KASAN_ABI_VERSION 3
#endif
#if GCC_VERSION >= 50000
#define CC_HAVE_BUILTIN_OVERFLOW
#endif
#endif /* gcc version >= 40000 specific checks */
#if !defined(__noclone)

18
include/linux/overflow-arith.h Normal file
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@ -0,0 +1,18 @@
#pragma once
#include <linux/kernel.h>
#ifdef CC_HAVE_BUILTIN_OVERFLOW
#define overflow_usub __builtin_usub_overflow
#else
static inline bool overflow_usub(unsigned int a, unsigned int b,
unsigned int *res)
{
*res = a - b;
return *res > a ? true : false;
}
#endif