Commit 79907146 authored Oct 16, 2015 by Hannes Frederic Sowa Committed by David S. Miller Oct 23, 2015

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



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>

parent c80dbe04

include/linux/compiler-gcc.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -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)

include/linux/overflow-arith.h

0 → 100644

+18 −0

Original line number	Diff line number	Diff line
		#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