From 79907146fb5b1778035870db895fb2bf64061284 Mon Sep 17 00:00:00 2001 From: Hannes Frederic Sowa Date: Fri, 16 Oct 2015 11:32:42 +0200 Subject: [PATCH] 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 Signed-off-by: David S. Miller --- include/linux/compiler-gcc.h | 4 ++++ include/linux/overflow-arith.h | 18 ++++++++++++++++++ 2 files changed, 22 insertions(+) create mode 100644 include/linux/overflow-arith.h diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index dfaa7b3e9ae9..82c159e0532a 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -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) diff --git a/include/linux/overflow-arith.h b/include/linux/overflow-arith.h new file mode 100644 index 000000000000..e12ccf854a70 --- /dev/null +++ b/include/linux/overflow-arith.h @@ -0,0 +1,18 @@ +#pragma once + +#include + +#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 -- 2.20.1