From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [203.10.76.45]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mx.ozlabs.org", Issuer "CA Cert Signing Authority" (verified OK)) by bilbo.ozlabs.org (Postfix) with ESMTPS id F12F0B6F56 for ; Fri, 11 Sep 2009 10:10:56 +1000 (EST) Received: from mail3.caviumnetworks.com (mail3.caviumnetworks.com [12.108.191.235]) by ozlabs.org (Postfix) with ESMTP id 7506ADDD0B for ; Fri, 11 Sep 2009 10:10:56 +1000 (EST) From: David Daney To: torvalds@linux-foundation.org, akpm@linux-foundation.org Subject: [PATCH 01/10] Add support for GCC-4.5's __builtin_unreachable() to compiler.h Date: Thu, 10 Sep 2009 16:56:42 -0700 Message-Id: <1252627011-2933-1-git-send-email-ddaney@caviumnetworks.com> In-Reply-To: <4AA991C1.1050800@caviumnetworks.com> References: <4AA991C1.1050800@caviumnetworks.com> Cc: linux-mips@linux-mips.org, Heiko Carstens , linuxppc-dev@ozlabs.org, Paul Mackerras , "H. Peter Anvin" , linux-s390@vger.kernel.org, linux-am33-list@redhat.com, Helge Deller , x86@kernel.org, David Daney , Ingo Molnar , Mike Frysinger , Ivan Kokshaysky , uclinux-dist-devel@blackfin.uclinux.org, Thomas Gleixner , Richard Henderson , Haavard Skinnemoen , linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org, ralf@linux-mips.org, Kyle McMartin , linux-alpha@vger.kernel.org, Martin Schwidefsky , linux390@de.ibm.com, Koichi Yasutake List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Starting with version 4.5, GCC has a new built-in function __builtin_unreachable() that can be used in places like the kernel's BUG() where inline assembly is used to transfer control flow. This eliminated the need for an endless loop in these places. The patch adds a new macro 'unreachable()' that will expand to either __builtin_unreachable() or an endless loop depending on the compiler version. Signed-off-by: David Daney CC: Thomas Gleixner CC: Ingo Molnar CC: "H. Peter Anvin" CC: x86@kernel.org CC: ralf@linux-mips.org CC: linux-mips@linux-mips.org CC: Martin Schwidefsky CC: Heiko Carstens CC: linux390@de.ibm.com CC: linux-s390@vger.kernel.org CC: David Howells CC: Koichi Yasutake CC: linux-am33-list@redhat.com CC: Kyle McMartin CC: Helge Deller CC: linux-parisc@vger.kernel.org CC: Benjamin Herrenschmidt CC: Paul Mackerras CC: linuxppc-dev@ozlabs.org CC: Richard Henderson CC: Ivan Kokshaysky CC: linux-alpha@vger.kernel.org CC: Haavard Skinnemoen CC: Mike Frysinger CC: uclinux-dist-devel@blackfin.uclinux.org --- include/linux/compiler-gcc4.h | 14 ++++++++++++++ include/linux/compiler.h | 5 +++++ 2 files changed, 19 insertions(+), 0 deletions(-) diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h index 450fa59..ab3af40 100644 --- a/include/linux/compiler-gcc4.h +++ b/include/linux/compiler-gcc4.h @@ -36,4 +36,18 @@ the kernel context */ #define __cold __attribute__((__cold__)) + +#if __GNUC_MINOR__ >= 5 +/* + * Mark a position in code as unreachable. This can be used to + * suppress control flow warnings after asm blocks that transfer + * control elsewhere. + * + * Early snapshots of gcc 4.5 don't support this and we can't detect + * this in the preprocessor, but we can live with this because they're + * unreleased. Really, we need to have autoconf for the kernel. + */ +#define unreachable() __builtin_unreachable() +#endif + #endif diff --git a/include/linux/compiler.h b/include/linux/compiler.h index 04fb513..7efd73f 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -144,6 +144,11 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); # define barrier() __memory_barrier() #endif +/* Unreachable code */ +#ifndef unreachable +# define unreachable() do { for (;;) ; } while (0) +#endif + #ifndef RELOC_HIDE # define RELOC_HIDE(ptr, off) \ ({ unsigned long __ptr; \ -- 1.6.2.5