| Message ID | 20180607183219.192973-2-ndesaulniers@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, 2018-06-07 at 11:32 -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 +72,22 @@ > * -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 > +#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 > +#define __inline inline > #endif Perhaps move these last 2 defines below the #endif as they are common to both cases #if !defined(CONFIG_ARCH_SUPPORTS_OPTIMIZED_INLINING) || \ !defined(CONFIG_OPTIMIZE_INLINING) || (__GNUC__ < 4) #define inline inline __attribute__((always_inline, unused, gnu_inline)) notrace #else /* A lot of inline functions can cause havoc with function tracing */ #define inline inline __attribute__((unused, gnu_inline)) notrace #endif #define __inline__ inline #define __inline inline #define __always_inline inline __attribute__((always_inline)) -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index b4bf73f5e38f..3365f20dba5a 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -72,17 +72,22 @@ * -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 +#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 +#define __inline inline #endif #define __always_inline inline __attribute__((always_inline))
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. Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Suggested-by: H. Peter Anvin <hpa@zytor.com> Suggested-by: Joe Perches <joe@perches.com> --- include/linux/compiler-gcc.h | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-)