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Date: Thu, 10 Oct 2013 10:55:06 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Jakub Jelinek <jakub@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Oleg Nesterov <oleg@...hat.com>,
Fengguang Wu <fengguang.wu@...el.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Richard Henderson <rth@...ddle.net>
Subject: [PATCH, -v2] compiler/gcc4: Add quirk for 'asm goto' miscompilation
bug
* Ingo Molnar <mingo@...nel.org> wrote:
> * Jakub Jelinek <jakub@...hat.com> wrote:
>
> > On Thu, Oct 10, 2013 at 10:24:30AM +0200, Ingo Molnar wrote:
> > > Something like the patch below? (Totally untested and all that.)
> > >
> > > Notes:
> > >
> > > - If the bug is fixed in 4.8.3 then the version check can be sharpened
> > > from 99999 to 40803.
> >
> > The bug is likely going to be fixed already for 4.8.2 (to be released
> > next week or so).
> >
> > > - I'd really prefer this quirk versus having to add the extra barrier to
> > > the label, as it makes the actual usage sites a lot less painful.
> >
> > Please check how much it bloats the generated code.
>
> on Linus's latest tree plain 'asm goto' is only rarely used, so the size
> impact of the patch, on x86-64 defconfig, is zero:
>
> vmlinux:
> text data bss dec hex filename
> 11166823 1448024 1187840 13802687 d29cbf vmlinux.before
> 11166823 1448024 1187840 13802687 d29cbf vmlinux.after
> 1f7c3c1fd71b4b1327965bcfbc7a77fb vmlinux.before
> 3b246add801bc170e47096b712942395 vmlinux.after
>
> Using GCC 4.8.1.
>
> > Also, for the bitops patch, you probably want an asm_volatile_goto variant.
>
> Also, for mutex_64.h - good point, will fix that.
See the updated patch below. I've added a 4.8.2 version cutoff.
Thanks,
Ingo
===================>
Subject: compiler/gcc4: Add quirk for 'asm goto' miscompilation bug
From: Ingo Molnar <mingo@...nel.org>
Date: Thu, 10 Oct 2013 10:16:30 +0200
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-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>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
arch/arm/include/asm/jump_label.h | 2 +-
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 | 6 +++---
arch/x86/include/asm/jump_label.h | 2 +-
arch/x86/include/asm/mutex_64.h | 4 ++--
include/linux/compiler-gcc4.h | 16 ++++++++++++++++
9 files changed, 27 insertions(+), 11 deletions(-)
Index: tip/arch/arm/include/asm/jump_label.h
===================================================================
--- tip.orig/arch/arm/include/asm/jump_label.h
+++ tip/arch/arm/include/asm/jump_label.h
@@ -16,7 +16,7 @@
static __always_inline bool arch_static_branch(struct static_key *key)
{
- asm goto("1:\n\t"
+ asm_goto("1:\n\t"
JUMP_LABEL_NOP "\n\t"
".pushsection __jump_table, \"aw\"\n\t"
".word 1b, %l[l_yes], %c0\n\t"
Index: tip/arch/mips/include/asm/jump_label.h
===================================================================
--- tip.orig/arch/mips/include/asm/jump_label.h
+++ tip/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_goto("1:\tnop\n\t"
"nop\n\t"
".pushsection __jump_table, \"aw\"\n\t"
WORD_INSN " 1b, %l[l_yes], %0\n\t"
Index: tip/arch/powerpc/include/asm/jump_label.h
===================================================================
--- tip.orig/arch/powerpc/include/asm/jump_label.h
+++ tip/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_goto("1:\n\t"
"nop\n\t"
".pushsection __jump_table, \"aw\"\n\t"
JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
Index: tip/arch/s390/include/asm/jump_label.h
===================================================================
--- tip.orig/arch/s390/include/asm/jump_label.h
+++ tip/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_goto("0: brcl 0,0\n"
".pushsection __jump_table, \"aw\"\n"
ASM_ALIGN "\n"
ASM_PTR " 0b, %l[label], %0\n"
Index: tip/arch/sparc/include/asm/jump_label.h
===================================================================
--- tip.orig/arch/sparc/include/asm/jump_label.h
+++ tip/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_goto("1:\n\t"
"nop\n\t"
"nop\n\t"
".pushsection __jump_table, \"aw\"\n\t"
Index: tip/arch/x86/include/asm/cpufeature.h
===================================================================
--- tip.orig/arch/x86/include/asm/cpufeature.h
+++ tip/arch/x86/include/asm/cpufeature.h
@@ -374,7 +374,7 @@ static __always_inline __pure bool __sta
* Catch too early usage of this before alternatives
* have run.
*/
- asm goto("1: jmp %l[t_warn]\n"
+ asm_goto("1: jmp %l[t_warn]\n"
"2:\n"
".section .altinstructions,\"a\"\n"
" .long 1b - .\n"
@@ -388,7 +388,7 @@ static __always_inline __pure bool __sta
#endif
- asm goto("1: jmp %l[t_no]\n"
+ asm_goto("1: jmp %l[t_no]\n"
"2:\n"
".section .altinstructions,\"a\"\n"
" .long 1b - .\n"
@@ -453,7 +453,7 @@ static __always_inline __pure bool _stat
* have. Thus, we force the jump to the widest, 4-byte, signed relative
* offset even though the last would often fit in less bytes.
*/
- asm goto("1: .byte 0xe9\n .long %l[t_dynamic] - 2f\n"
+ asm_goto("1: .byte 0xe9\n .long %l[t_dynamic] - 2f\n"
"2:\n"
".section .altinstructions,\"a\"\n"
" .long 1b - .\n" /* src offset */
Index: tip/arch/x86/include/asm/jump_label.h
===================================================================
--- tip.orig/arch/x86/include/asm/jump_label.h
+++ tip/arch/x86/include/asm/jump_label.h
@@ -18,7 +18,7 @@
static __always_inline bool arch_static_branch(struct static_key *key)
{
- asm goto("1:"
+ asm_goto("1:"
".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
".pushsection __jump_table, \"aw\" \n\t"
_ASM_ALIGN "\n\t"
Index: tip/arch/x86/include/asm/mutex_64.h
===================================================================
--- tip.orig/arch/x86/include/asm/mutex_64.h
+++ tip/arch/x86/include/asm/mutex_64.h
@@ -20,7 +20,7 @@
static inline void __mutex_fastpath_lock(atomic_t *v,
void (*fail_fn)(atomic_t *))
{
- asm volatile goto(LOCK_PREFIX " decl %0\n"
+ asm_volatile_goto(LOCK_PREFIX " decl %0\n"
" jns %l[exit]\n"
: : "m" (v->counter)
: "memory", "cc"
@@ -75,7 +75,7 @@ static inline int __mutex_fastpath_lock_
static inline void __mutex_fastpath_unlock(atomic_t *v,
void (*fail_fn)(atomic_t *))
{
- asm volatile goto(LOCK_PREFIX " incl %0\n"
+ asm_volatile_goto(LOCK_PREFIX " incl %0\n"
" jg %l[exit]\n"
: : "m" (v->counter)
: "memory", "cc"
Index: tip/include/linux/compiler-gcc4.h
===================================================================
--- tip.orig/include/linux/compiler-gcc4.h
+++ tip/include/linux/compiler-gcc4.h
@@ -65,6 +65,22 @@
#define __visible __attribute__((externally_visible))
#endif
+/*
+ * GCC 'asm goto' miscompiles certain code sequences:
+ *
+ * http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
+ *
+ * Work it around via quirk suggested by Jakub Jelinek.
+ * Fixed in GCC 4.8.2 and later versions.
+ */
+#if GCC_VERSION <= 40801
+# define __asm_goto(vol, x...) do { asm vol goto(x); asm (""); } while (0)
+#else
+# define __asm_goto(vol, x...) do { asm vol goto(x); } while (0)
+#endif
+
+#define asm_goto(x...) __asm_goto(,x)
+#define asm_volatile_goto(x...) __asm_goto(volatile, x)
#ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP
#if GCC_VERSION >= 40400
--
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