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ARM: kprobes: enable OPTPROBES for ARM 32

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This patch introduce kprobeopt for ARM 32.

Limitations:
 - Currently only kernel compiled with ARM ISA is supported.

 - Offset between probe point and optinsn slot must not larger than
   32MiB. Masami Hiramatsu suggests replacing 2 words, it will make
   things complex. Futher patch can make such optimization.

Kprobe opt on ARM is relatively simpler than kprobe opt on x86 because
ARM instruction is always 4 bytes aligned and 4 bytes long. This patch
replace probed instruction by a 'b', branch to trampoline code and then
calls optimized_callback(). optimized_callback() calls opt_pre_handler()
to execute kprobe handler. It also emulate/simulate replaced instruction.

When unregistering kprobe, the deferred manner of unoptimizer may leave
branch instruction before optimizer is called. Different from x86_64,
which only copy the probed insn after optprobe_template_end and
reexecute them, this patch call singlestep to emulate/simulate the insn
directly. Futher patch can optimize this behavior.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Will Deacon <will.deacon@arm.com>
Reviewed-by: Jon Medhurst (Tixy) <tixy@linaro.org>
Signed-off-by: Jon Medhurst <tixy@linaro.org>
This commit is contained in:
Wang Nan
2015-01-09 14:37:36 +08:00
committed by Jon Medhurst
parent cbf6ab52ad
commit 0dc016dbd8
10 changed files with 377 additions and 12 deletions
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29
arch/arm/include/asm/kprobes.h
View File

@@ -50,5 +50,34 @@ int kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr);
int kprobe_exceptions_notify(struct notifier_block *self,
unsigned long val, void *data);
/* optinsn template addresses */
extern __visible kprobe_opcode_t optprobe_template_entry;
extern __visible kprobe_opcode_t optprobe_template_val;
extern __visible kprobe_opcode_t optprobe_template_call;
extern __visible kprobe_opcode_t optprobe_template_end;
extern __visible kprobe_opcode_t optprobe_template_sub_sp;
extern __visible kprobe_opcode_t optprobe_template_add_sp;
#define MAX_OPTIMIZED_LENGTH 4
#define MAX_OPTINSN_SIZE \
((unsigned long)&optprobe_template_end - \
(unsigned long)&optprobe_template_entry)
#define RELATIVEJUMP_SIZE 4
struct arch_optimized_insn {
/*
* copy of the original instructions.
* Different from x86, ARM kprobe_opcode_t is u32.
*/
#define MAX_COPIED_INSN DIV_ROUND_UP(RELATIVEJUMP_SIZE, sizeof(kprobe_opcode_t))
kprobe_opcode_t copied_insn[MAX_COPIED_INSN];
/* detour code buffer */
kprobe_opcode_t *insn;
/*
* We always copy one instruction on ARM,
* so size will always be 4, and unlike x86, there is no
* need for a size field.
*/
};
#endif /* _ARM_KPROBES_H */