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SubjectRe: [PATCH v18 11/11] ARM: optprobes: execute instruction during restoring if possible.
(2014/12/29 13:07), Wang Nan wrote:
> This patch removes software emulation or simulation for most of probed
> instructions. If the instruction doesn't use PC relative addressing,
> it will be translated into following instructions in the restore code
> in code template:
>
> ldmia {r0 - r14} // restore all instruction except PC
> <instruction> // direct execute the probed instruction
> b next_insn // branch to next instruction.
>
> Signed-off-by: Wang Nan <wangnan0@huawei.com>

Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

[...]
> /*
> + * See register_usage_mask. If the probed instruction doesn't use PC,
> + * we can copy it into template and have it executed directly without
> + * simulation or emulation.
> + */
> +#define can_kprobe_direct_exec(m) (!((m) & __register_usage_mask(15)))

BTW, is there any macro which indicates 15 is the number of PC register?
If we can do something like below, it will be easier to understand.

#define can_kprobe_direct_exec(m) (!test_bit(ARM_REG_PC/* == 15*/, &m))

Thank you,

> +
> +/*
> * NOTE: the first sub and add instruction will be modified according
> * to the stack cost of the instruction.
> */
> @@ -66,7 +73,15 @@ asm (
> " orrne r2, #1\n"
> " strne r2, [sp, #60] @ set bit0 of PC for thumb\n"
> " msr cpsr_cxsf, r1\n"
> + ".global optprobe_template_restore_begin\n"
> + "optprobe_template_restore_begin:\n"
> " ldmia sp, {r0 - r15}\n"
> + ".global optprobe_template_restore_orig_insn\n"
> + "optprobe_template_restore_orig_insn:\n"
> + " nop\n"
> + ".global optprobe_template_restore_end\n"
> + "optprobe_template_restore_end:\n"
> + " nop\n"
> ".global optprobe_template_val\n"
> "optprobe_template_val:\n"
> "1: .long 0\n"
> @@ -86,6 +101,12 @@ asm (
> ((unsigned long *)&optprobe_template_add_sp - (unsigned long *)&optprobe_template_entry)
> #define TMPL_SUB_SP \
> ((unsigned long *)&optprobe_template_sub_sp - (unsigned long *)&optprobe_template_entry)
> +#define TMPL_RESTORE_BEGIN \
> + ((unsigned long *)&optprobe_template_restore_begin - (unsigned long *)&optprobe_template_entry)
> +#define TMPL_RESTORE_ORIGN_INSN \
> + ((unsigned long *)&optprobe_template_restore_orig_insn - (unsigned long *)&optprobe_template_entry)
> +#define TMPL_RESTORE_END \
> + ((unsigned long *)&optprobe_template_restore_end - (unsigned long *)&optprobe_template_entry)
>
> /*
> * ARM can always optimize an instruction when using ARM ISA, except
> @@ -155,8 +176,12 @@ optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
> __this_cpu_write(current_kprobe, NULL);
> }
>
> - /* In each case, we must singlestep the replaced instruction. */
> - op->kp.ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
> + /*
> + * We singlestep the replaced instruction only when it can't be
> + * executed directly during restore.
> + */
> + if (!p->ainsn.kprobe_direct_exec)
> + op->kp.ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
>
> local_irq_restore(flags);
> }
> @@ -238,6 +263,28 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *or
> val = (unsigned long)optimized_callback;
> code[TMPL_CALL_IDX] = val;
>
> + /* If possible, copy insn and have it executed during restore */
> + orig->ainsn.kprobe_direct_exec = false;
> + if (can_kprobe_direct_exec(orig->ainsn.register_usage_mask)) {
> + kprobe_opcode_t final_branch = arm_gen_branch(
> + (unsigned long)(&code[TMPL_RESTORE_END]),
> + (unsigned long)(op->kp.addr) + 4);
> + if (final_branch != 0) {
> + /*
> + * Replace original 'ldmia sp, {r0 - r15}' with
> + * 'ldmia {r0 - r14}', restore all registers except pc.
> + */
> + code[TMPL_RESTORE_BEGIN] = __opcode_to_mem_arm(0xe89d7fff);
> +
> + /* The original probed instruction */
> + code[TMPL_RESTORE_ORIGN_INSN] = __opcode_to_mem_arm(orig->opcode);
> +
> + /* Jump back to next instruction */
> + code[TMPL_RESTORE_END] = __opcode_to_mem_arm(final_branch);
> + orig->ainsn.kprobe_direct_exec = true;
> + }
> + }
> +
> flush_icache_range((unsigned long)code,
> (unsigned long)(&code[TMPL_END_IDX]));
>
>


--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com



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