linux-sg2042/include/linux/jump_label.h

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#ifndef _LINUX_JUMP_LABEL_H
#define _LINUX_JUMP_LABEL_H
jump label: Add work around to i386 gcc asm goto bug On i386 (not x86_64) early implementations of gcc would have a bug with asm goto causing it to produce code like the following: (This was noticed by Peter Zijlstra) 56 pushl 0 67 nopl jmp 0x6f popl jmp 0x8c 6f mov test je 0x8c 8c mov call *(%esp) The jump added in the asm goto skipped over the popl that matched the pushl 0, which lead up to a quick crash of the system when the jump was enabled. The nopl is defined in the asm goto () statement and when tracepoints are enabled, the nop changes to a jump to the label that was specified by the asm goto. asm goto is suppose to tell gcc that the code in the asm might jump to an external label. Here gcc obviously fails to make that work. The bug report for gcc is here: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46226 The bug only appears on x86 when not compiled with -maccumulate-outgoing-args. This option is always set on x86_64 and it is also the work around for a function graph tracer i386 bug. (See commit: 746357d6a526d6da9d89a2ec645b28406e959c2e) This explains why the bug only showed up on i386 when function graph tracer was not enabled. This patch now adds a CONFIG_JUMP_LABEL option that is default off instead of using jump labels by default. When jump labels are enabled, the -maccumulate-outgoing-args will be used (causing a slightly larger kernel image on i386). This option will exist until we have a way to detect if the gcc compiler in use is safe to use on all configurations without the work around. Note, there exists such a test, but for now we will keep the enabling of jump label as a manual option. Archs that know the compiler is safe with asm goto, may choose to select JUMP_LABEL and enable it by default. Reported-by: Ingo Molnar <mingo@elte.hu> Cause-discovered-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Jason Baron <jbaron@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: David Daney <ddaney@caviumnetworks.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: David Miller <davem@davemloft.net> Cc: Richard Henderson <rth@redhat.com> LKML-Reference: <1288028746.3673.11.camel@laptop> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2010-10-30 00:33:43 +08:00
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
# include <asm/jump_label.h>
# define HAVE_JUMP_LABEL
#endif
enum jump_label_type {
JUMP_LABEL_ENABLE,
JUMP_LABEL_DISABLE
};
struct module;
#ifdef HAVE_JUMP_LABEL
extern struct jump_entry __start___jump_table[];
extern struct jump_entry __stop___jump_table[];
extern void jump_label_lock(void);
extern void jump_label_unlock(void);
extern void arch_jump_label_transform(struct jump_entry *entry,
enum jump_label_type type);
extern void arch_jump_label_text_poke_early(jump_label_t addr);
extern void jump_label_update(unsigned long key, enum jump_label_type type);
extern void jump_label_apply_nops(struct module *mod);
extern int jump_label_text_reserved(void *start, void *end);
#define jump_label_enable(key) \
jump_label_update((unsigned long)key, JUMP_LABEL_ENABLE);
#define jump_label_disable(key) \
jump_label_update((unsigned long)key, JUMP_LABEL_DISABLE);
#else
#define JUMP_LABEL(key, label) \
do { \
if (unlikely(*key)) \
goto label; \
} while (0)
#define jump_label_enable(cond_var) \
do { \
*(cond_var) = 1; \
} while (0)
#define jump_label_disable(cond_var) \
do { \
*(cond_var) = 0; \
} while (0)
static inline int jump_label_apply_nops(struct module *mod)
{
return 0;
}
static inline int jump_label_text_reserved(void *start, void *end)
{
return 0;
}
static inline void jump_label_lock(void) {}
static inline void jump_label_unlock(void) {}
#endif
#define COND_STMT(key, stmt) \
do { \
__label__ jl_enabled; \
JUMP_LABEL(key, jl_enabled); \
if (0) { \
jl_enabled: \
stmt; \
} \
} while (0)
#endif