From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756814Ab2HOUXi (ORCPT ); Wed, 15 Aug 2012 16:23:38 -0400 Received: from mail.windriver.com ([147.11.1.11]:36810 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756603Ab2HOTud (ORCPT ); Wed, 15 Aug 2012 15:50:33 -0400 From: Paul Gortmaker To: , CC: Josh Stone , Masami Hiramatsu , Jakub Jelinek , Linus Torvalds , Paul Gortmaker Subject: [v2.6.34-stable 069/165] x86: Fix compilation bug in kprobes' twobyte_is_boostable Date: Wed, 15 Aug 2012 15:46:53 -0400 Message-ID: <1345060109-9187-70-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.7.12.rc2 In-Reply-To: <1345060109-9187-1-git-send-email-paul.gortmaker@windriver.com> References: <1345060109-9187-1-git-send-email-paul.gortmaker@windriver.com> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Josh Stone ------------------- This is a commit scheduled for the next v2.6.34 longterm release. http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git If you see a problem with using this for longterm, please comment. ------------------- commit 315eb8a2a1b7f335d40ceeeb11b9e067475eb881 upstream. When compiling an i386_defconfig kernel with gcc-4.6.1-9.fc15.i686, I noticed a warning about the asm operand for test_bit in kprobes' can_boost. I discovered that this caused only the first long of twobyte_is_boostable[] to be output. Jakub filed and fixed gcc PR50571 to correct the warning and this output issue. But to solve it for less current gcc, we can make kprobes' twobyte_is_boostable[] non-const, and it won't be optimized out. Before: CC arch/x86/kernel/kprobes.o In file included from include/linux/bitops.h:22:0, from include/linux/kernel.h:17, from [...]/arch/x86/include/asm/percpu.h:44, from [...]/arch/x86/include/asm/current.h:5, from [...]/arch/x86/include/asm/processor.h:15, from [...]/arch/x86/include/asm/atomic.h:6, from include/linux/atomic.h:4, from include/linux/mutex.h:18, from include/linux/notifier.h:13, from include/linux/kprobes.h:34, from arch/x86/kernel/kprobes.c:43: [...]/arch/x86/include/asm/bitops.h: In function ‘can_boost.part.1’: [...]/arch/x86/include/asm/bitops.h:319:2: warning: use of memory input without lvalue in asm operand 1 is deprecated [enabled by default] $ objdump -rd arch/x86/kernel/kprobes.o | grep -A1 -w bt 551: 0f a3 05 00 00 00 00 bt %eax,0x0 554: R_386_32 .rodata.cst4 $ objdump -s -j .rodata.cst4 -j .data arch/x86/kernel/kprobes.o arch/x86/kernel/kprobes.o: file format elf32-i386 Contents of section .data: 0000 48000000 00000000 00000000 00000000 H............... Contents of section .rodata.cst4: 0000 4c030000 L... Only a single long of twobyte_is_boostable[] is in the object file. After, without the const on twobyte_is_boostable: $ objdump -rd arch/x86/kernel/kprobes.o | grep -A1 -w bt 551: 0f a3 05 20 00 00 00 bt %eax,0x20 554: R_386_32 .data $ objdump -s -j .rodata.cst4 -j .data arch/x86/kernel/kprobes.o arch/x86/kernel/kprobes.o: file format elf32-i386 Contents of section .data: 0000 48000000 00000000 00000000 00000000 H............... 0010 00000000 00000000 00000000 00000000 ................ 0020 4c030000 0f000200 ffff0000 ffcff0c0 L............... 0030 0000ffff 3bbbfff8 03ff2ebb 26bb2e77 ....;.......&..w Now all 32 bytes are output into .data instead. Signed-off-by: Josh Stone Cc: Masami Hiramatsu Cc: Jakub Jelinek Signed-off-by: Linus Torvalds Signed-off-by: Paul Gortmaker --- arch/x86/kernel/kprobes.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c index ac4ed92..9619315 100644 --- a/arch/x86/kernel/kprobes.c +++ b/arch/x86/kernel/kprobes.c @@ -75,8 +75,10 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk); /* * Undefined/reserved opcodes, conditional jump, Opcode Extension * Groups, and some special opcodes can not boost. + * This is non-const to keep gcc from statically optimizing it out, as + * variable_test_bit makes gcc think only *(unsigned long*) is used. */ -static const u32 twobyte_is_boostable[256 / 32] = { +static u32 twobyte_is_boostable[256 / 32] = { /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */ /* ---------------------------------------------- */ W(0x00, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0) | /* 00 */ -- 1.7.12.rc2