linux-kernel - [PATCH 3.4 007/134] compiler/gcc4: Add quirk for asm goto miscompilation bug

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Date:	Wed,  9 Apr 2014 20:22:03 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Jakub Jelinek <jakub@...hat.com>,
	Richard Henderson <rth@...ddle.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Ben Hutchings <ben@...adent.org.uk>,
	Qiang Huang <h.huangqiang@...wei.com>,
	Li Zefan <lizefan@...wei.com>,
	Jianguo Wu <wujianguo@...wei.com>
Subject: [PATCH 3.4 007/134] compiler/gcc4: Add quirk for asm goto miscompilation bug

3.4-stable 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
[hq: Backported to 3.4: Adjust context]
Signed-off-by: Qiang Huang <h.huangqiang@...wei.com>
Cc: Li Zefan <lizefan@...wei.com>
Cc: Jianguo Wu <wujianguo@...wei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/mips/include/asm/jump_label.h    |    2 +-
 arch/powerpc/include/asm/jump_label.h |    2 +-
 arch/s390/include/asm/jump_label.h    |    2 +-
 arch/sparc/include/asm/jump_label.h   |    2 +-
 arch/x86/include/asm/cpufeature.h     |    2 +-
 arch/x86/include/asm/jump_label.h     |    2 +-
 include/linux/compiler-gcc4.h         |   16 ++++++++++++++++
 7 files changed, 22 insertions(+), 6 deletions(-)

--- 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 static_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 static_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 static_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 static_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
@@ -342,7 +342,7 @@ 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 static_key *key)
 {
-	asm goto("1:"
+	asm_volatile_goto("1:"
 		STATIC_KEY_INITIAL_NOP
 		".pushsection __jump_table,  \"aw\" \n\t"
 		_ASM_ALIGN "\n\t"
--- a/include/linux/compiler-gcc4.h
+++ b/include/linux/compiler-gcc4.h
@@ -31,6 +31,22 @@
 
 #define __linktime_error(message) __attribute__((__error__(message)))
 
+/*
+ * 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
 /*
  * Mark a position in code as unreachable.  This can be used to


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