From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Daney Subject: [PATCH 00/10] Add support for GCC's __builtin_unreachable() and use it in BUG. Date: Thu, 10 Sep 2009 16:54:41 -0700 Message-ID: <4AA991C1.1050800@caviumnetworks.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-alpha-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Linus Torvalds , Andrew Morton Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, ralf@linux-mips.org, linux-mips@linux-mips.org, Martin Schwidefsky , Heiko Carstens , linux390@de.ibm.com, linux-s390@vger.kernel.org, David Howells , Koichi Yasutake , linux-am33-list@redhat.com, Kyle McMartin , Helge Deller , linux-parisc@vger.kernel.org, Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@ozlabs.org, Richard Henderson , Ivan Kokshaysky , linux-alpha@vger.kernel.org, Haavard Skinnemoen , Mike Frysinger , uclinux-dist-devel@blackfin.uclinux.org Starting with version 4.5, GCC has a new built-in function called __builtin_unreachable(). The function tells the compiler that control flow will never reach that point. Currently we trick the compiler by putting in for(;;); but this has the disadvantage that extra code is emitted for an endless loop. For an i386 kernel using __builtin_unreachable() results in an allyesconfig that is nearly 4000 bytes smaller. This patch set adds support to compiler.h creating a new macro usable in the kernel called unreachable(). If the compiler lacks __builtin_unreachable(), it just expands to for(;;). The x86 and MIPS patches I actually tested with a GCC-4.5 snapshot. Lacking the ability to test the rest of the architectures, I just did what seemed right without even trying to compile the kernel. 01/10 adds the compiler.h support, the rest of the patches retrofit the various architecture BUG macros to use it instead of for(;;) or while(1) loops. I will reply with the 10 patches. The architecture specific patches I will send to a smaller set of people. David Daney (10): Add support for GCC-4.5's __builtin_unreachable() to compiler.h x86: Convert BUG() to use unreachable() MIPS: Convert BUG() to use unreachable() s390: Convert BUG() to use unreachable() mn10300: Convert BUG() to use unreachable() parisc: Convert BUG() to use unreachable() powerpc: Convert BUG() to use unreachable() alpha: Convert BUG() to use unreachable() avr32: Convert BUG() to use unreachable() blackfin: Convert BUG() to use unreachable() arch/alpha/include/asm/bug.h | 2 +- arch/avr32/include/asm/bug.h | 2 +- arch/blackfin/include/asm/bug.h | 2 +- arch/mips/include/asm/bug.h | 4 +--- arch/mn10300/include/asm/bug.h | 3 ++- arch/parisc/include/asm/bug.h | 4 ++-- arch/powerpc/include/asm/bug.h | 2 +- arch/s390/include/asm/bug.h | 2 +- arch/x86/include/asm/bug.h | 4 ++-- include/linux/compiler-gcc4.h | 14 ++++++++++++++ include/linux/compiler.h | 5 +++++ 11 files changed, 31 insertions(+), 13 deletions(-)