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45f81b1c96
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: 746357d6a5)
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>
79 lines
1.7 KiB
C
79 lines
1.7 KiB
C
#ifndef _LINUX_JUMP_LABEL_H
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#define _LINUX_JUMP_LABEL_H
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#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
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# include <asm/jump_label.h>
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# define HAVE_JUMP_LABEL
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#endif
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enum jump_label_type {
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JUMP_LABEL_ENABLE,
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JUMP_LABEL_DISABLE
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};
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struct module;
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#ifdef HAVE_JUMP_LABEL
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extern struct jump_entry __start___jump_table[];
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extern struct jump_entry __stop___jump_table[];
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extern void jump_label_lock(void);
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extern void jump_label_unlock(void);
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extern void arch_jump_label_transform(struct jump_entry *entry,
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enum jump_label_type type);
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extern void arch_jump_label_text_poke_early(jump_label_t addr);
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extern void jump_label_update(unsigned long key, enum jump_label_type type);
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extern void jump_label_apply_nops(struct module *mod);
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extern int jump_label_text_reserved(void *start, void *end);
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#define jump_label_enable(key) \
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jump_label_update((unsigned long)key, JUMP_LABEL_ENABLE);
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#define jump_label_disable(key) \
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jump_label_update((unsigned long)key, JUMP_LABEL_DISABLE);
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#else
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#define JUMP_LABEL(key, label) \
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do { \
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if (unlikely(*key)) \
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goto label; \
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} while (0)
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#define jump_label_enable(cond_var) \
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do { \
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*(cond_var) = 1; \
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} while (0)
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#define jump_label_disable(cond_var) \
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do { \
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*(cond_var) = 0; \
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} while (0)
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static inline int jump_label_apply_nops(struct module *mod)
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{
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return 0;
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}
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static inline int jump_label_text_reserved(void *start, void *end)
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{
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return 0;
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}
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static inline void jump_label_lock(void) {}
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static inline void jump_label_unlock(void) {}
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#endif
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#define COND_STMT(key, stmt) \
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do { \
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__label__ jl_enabled; \
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JUMP_LABEL(key, jl_enabled); \
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if (0) { \
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jl_enabled: \
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stmt; \
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} \
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} while (0)
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#endif
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