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From: Joe Perches <joe@perches.com>
To: Nick Desaulniers <ndesaulniers@google.com>,
	akpm@linux-foundation.org, hpa@zytor.com, mingo@redhat.com,
	tglx@linutronix.de
Cc: linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org,
	x86@kernel.org, virtualization@lists.linux-foundation.org,
	astrachan@google.com, manojgupta@google.com,
	ghackmann@google.com, sedat.dilek@gmail.com, tstellar@redhat.com,
	keescook@google.com, yamada.masahiro@socionext.com,
	michal.lkml@markovi.net, linux-kbuild@vger.kernel.org,
	geert@linux-m68k.org, will.deacon@arm.com,
	mawilcox@microsoft.com, arnd@arndb.de, rientjes@google.com,
	acme@redhat.com, pombredanne@nexb.com, aryabinin@virtuozzo.com,
	kstewart@linuxfoundation.org, boris.ostrovsky@oracle.com,
	jan.kiszka@siemens.com, rostedt@goodmis.org,
	kirill.shutemov@linux.intel.com, ard.biesheuvel@linaro.org,
	akataria@vmware.com, brijesh.singh@amd.com,
	caoj.fnst@cn.fujitsu.com, gregkh@linuxfoundation.org,
	jarkko.sakkinen@linux.intel.com, jgross@suse.com,
	jpoimboe@redhat.com, mka@chromium.org, thomas.lendacky@amd.com,
	tweek@google.com, mjg59@google.com
Subject: Re: [PATCH v3 1/3] compiler-gcc.h: add gnu_inline to all inline declarations
Date: Thu, 07 Jun 2018 11:43:58 -0700	[thread overview]
Message-ID: <c58f58de39332a27f48dd485eab19a32c289a682.camel@perches.com> (raw)
In-Reply-To: <20180607183219.192973-2-ndesaulniers@google.com>

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))

  reply	other threads:[~2018-06-07 18:44 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-07 18:32 [PATCH v3 0/3] extern inline native_save_fl for paravirt Nick Desaulniers
2018-06-07 18:32 ` [PATCH v3 1/3] compiler-gcc.h: add gnu_inline to all inline declarations Nick Desaulniers
2018-06-07 18:43   ` Joe Perches [this message]
2018-06-07 18:32 ` [PATCH v3 2/3] x86/asm: add _ASM_ARG* constants for argument registers to <asm/asm.h> Nick Desaulniers
2018-06-07 20:13   ` H. Peter Anvin
2018-06-07 20:15     ` Nick Desaulniers
2018-06-07 18:32 ` [PATCH v3 3/3] x86: paravirt: make native_save_fl extern inline Nick Desaulniers
2018-06-07 18:39   ` Nick Desaulniers

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