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. [] > diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h [] > @@ -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 -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
