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Message-ID: <lsq.1385387069.415319245@decadent.org.uk>
Date: Mon, 25 Nov 2013 13:44:29 +0000
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC: akpm@...ux-foundation.org,
"Linus Torvalds" <torvalds@...ux-foundation.org>,
"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
"Oleg Nesterov" <oleg@...hat.com>,
"Richard Henderson" <rth@...ddle.net>,
"Ingo Molnar" <mingo@...nel.org>,
"Jakub Jelinek" <jakub@...hat.com>
Subject: [PATCH 3.2 60/87] compiler/gcc4: Add quirk for 'asm goto'
miscompilation bug
3.2.53-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Ingo Molnar <mingo@...nel.org>
commit 3f0116c3238a96bc18ad4b4acefe4e7be32fa861 upstream.
Fengguang Wu, Oleg Nesterov and Peter Zijlstra tracked down
a kernel crash to a GCC bug: GCC miscompiles certain 'asm goto'
constructs, as outlined here:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
Implement a workaround suggested by Jakub Jelinek.
Reported-and-tested-by: Fengguang Wu <fengguang.wu@...el.com>
Reported-by: Oleg Nesterov <oleg@...hat.com>
Reported-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Suggested-by: Jakub Jelinek <jakub@...hat.com>
Reviewed-by: Richard Henderson <rth@...ddle.net>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
[bwh: Backported to 3.2:
- Drop inapplicable changes
- Adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/arch/mips/include/asm/jump_label.h
+++ b/arch/mips/include/asm/jump_label.h
@@ -22,7 +22,7 @@
static __always_inline bool arch_static_branch(struct jump_label_key *key)
{
- asm goto("1:\tnop\n\t"
+ asm_volatile_goto("1:\tnop\n\t"
"nop\n\t"
".pushsection __jump_table, \"aw\"\n\t"
WORD_INSN " 1b, %l[l_yes], %0\n\t"
--- a/arch/powerpc/include/asm/jump_label.h
+++ b/arch/powerpc/include/asm/jump_label.h
@@ -19,7 +19,7 @@
static __always_inline bool arch_static_branch(struct jump_label_key *key)
{
- asm goto("1:\n\t"
+ asm_volatile_goto("1:\n\t"
"nop\n\t"
".pushsection __jump_table, \"aw\"\n\t"
JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
--- a/arch/s390/include/asm/jump_label.h
+++ b/arch/s390/include/asm/jump_label.h
@@ -15,7 +15,7 @@
static __always_inline bool arch_static_branch(struct jump_label_key *key)
{
- asm goto("0: brcl 0,0\n"
+ asm_volatile_goto("0: brcl 0,0\n"
".pushsection __jump_table, \"aw\"\n"
ASM_ALIGN "\n"
ASM_PTR " 0b, %l[label], %0\n"
--- a/arch/sparc/include/asm/jump_label.h
+++ b/arch/sparc/include/asm/jump_label.h
@@ -9,7 +9,7 @@
static __always_inline bool arch_static_branch(struct jump_label_key *key)
{
- asm goto("1:\n\t"
+ asm_volatile_goto("1:\n\t"
"nop\n\t"
"nop\n\t"
".pushsection __jump_table, \"aw\"\n\t"
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -334,7 +334,7 @@ extern const char * const x86_power_flag
static __always_inline __pure bool __static_cpu_has(u16 bit)
{
#if __GNUC__ > 4 || __GNUC_MINOR__ >= 5
- asm goto("1: jmp %l[t_no]\n"
+ asm_volatile_goto("1: jmp %l[t_no]\n"
"2:\n"
".section .altinstructions,\"a\"\n"
" .long 1b - .\n"
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -13,7 +13,7 @@
static __always_inline bool arch_static_branch(struct jump_label_key *key)
{
- asm goto("1:"
+ asm_volatile_goto("1:"
JUMP_LABEL_INITIAL_NOP
".pushsection __jump_table, \"aw\" \n\t"
_ASM_ALIGN "\n\t"
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -29,6 +29,21 @@
the kernel context */
#define __cold __attribute__((__cold__))
+/*
+ * GCC 'asm goto' miscompiles certain code sequences:
+ *
+ * http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
+ *
+ * Work it around via a compiler barrier quirk suggested by Jakub Jelinek.
+ * Fixed in GCC 4.8.2 and later versions.
+ *
+ * (asm goto is automatically volatile - the naming reflects this.)
+ */
+#if GCC_VERSION <= 40801
+# define asm_volatile_goto(x...) do { asm goto(x); asm (""); } while (0)
+#else
+# define asm_volatile_goto(x...) do { asm goto(x); } while (0)
+#endif
#if __GNUC_MINOR__ >= 5
/*
--
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