Re: [PATCH v2 1/2] compiler-gcc.h: add gnu_inline to all inline declarations
From: Joe Perches <joe@perches.com>
Date: 2018-06-05 17:23:40
On Tue, 2018-06-05 at 10:05 -0700, Nick Desaulniers wrote:
Functions marked extern inline do not emit an externally visible function when the gnu89 C standard is used. Some KBUILD Makefiles overwrite KBUILD_CFLAGS. This is an issue for GCC 5.1+ users as without an explicit C standard specified, the default is gnu11. Since c99, the semantics of extern inline have changed such that an externally visible function is always emitted. This can lead to multiple definition errors of extern inline functions at link time of compilation units whose build files have removed an explicit C standard compiler flag for users of GCC 5.1+ or Clang.
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diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
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@@ -72,17 +72,24 @@ * -Wunused-function. This turns out to avoid the need for complex #ifdef * directives. Suppress the warning in clang as well by using "unused" * function attribute, which is redundant but not harmful for gcc. + * Prefer gnu_inline, so that extern inline functions do not emit an + * externally visible function. This makes extern inline behave as per gnu89 + * semantics rather than c99. This prevents multiple symbol definition errors + * of extern inline functions at link time. */ #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \ !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4) -#define inline inline __attribute__((always_inline,unused)) notrace -#define __inline__ __inline__ __attribute__((always_inline,unused)) notrace -#define __inline __inline __attribute__((always_inline,unused)) notrace +#define inline \ + inline __attribute__((always_inline, unused, gnu_inline)) notrace +#define __inline__ \ + __inline__ __attribute__((always_inline, unused, gnu_inline)) notrace +#define __inline \ + __inline __attribute__((always_inline, unused, gnu_inline)) notrace
Perhaps these are simpler as #define __inline__ inline #define __inline inline
#else /* A lot of inline functions can cause havoc with function tracing */ -#define inline inline __attribute__((unused)) notrace -#define __inline__ __inline__ __attribute__((unused)) notrace -#define __inline __inline __attribute__((unused)) notrace +#define inline inline __attribute__((unused, gnu_inline)) notrace +#define __inline__ __inline__ __attribute__((unused, gnu_inline)) notrace +#define __inline __inline __attribute__((unused, gnu_inline)) notrace #endif
And only set once along with:
#define __always_inline inline __attribute__((always_inline))
And perhaps this __always_inline should be updated with gnu_inline as well