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Message-ID: <54A07FBE.3010206@hitachi.com>
Date: Mon, 29 Dec 2014 07:10:06 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To: Wang Nan <wangnan0@...wei.com>
Cc: tixy@...aro.org, linux@....linux.org.uk, lizefan@...wei.com,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v17 11/11] ARM: optprobes: execute instruction during
restoring if possible.
(2014/12/27 16:36), 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@...wei.com>
> ---
> arch/arm/include/asm/kprobes.h | 3 +++
> arch/arm/include/asm/probes.h | 1 +
> arch/arm/probes/kprobes/opt-arm.c | 47 +++++++++++++++++++++++++++++++++++++--
> 3 files changed, 49 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/include/asm/kprobes.h b/arch/arm/include/asm/kprobes.h
> index 50ff3bc..3ea9be5 100644
> --- a/arch/arm/include/asm/kprobes.h
> +++ b/arch/arm/include/asm/kprobes.h
> @@ -57,6 +57,9 @@ 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;
> +extern __visible kprobe_opcode_t optprobe_template_restore_begin;
> +extern __visible kprobe_opcode_t optprobe_template_restore_orig_insn;
> +extern __visible kprobe_opcode_t optprobe_template_restore_end;
>
> #define MAX_OPTIMIZED_LENGTH 4
> #define MAX_OPTINSN_SIZE \
> diff --git a/arch/arm/include/asm/probes.h b/arch/arm/include/asm/probes.h
> index ee8725c..8ebbe83 100644
> --- a/arch/arm/include/asm/probes.h
> +++ b/arch/arm/include/asm/probes.h
> @@ -50,6 +50,7 @@ struct arch_probes_insn {
> #define set_register_nouse(m, n) __clear_register_flag(m, n, REG_NO_USE)
> #define set_register_use(m, n) __set_register_flag(m, n, REG_USE)
> int register_usage_mask;
> + bool kprobe_direct_exec;
> };
>
> #endif /* __ASSEMBLY__ */
> diff --git a/arch/arm/probes/kprobes/opt-arm.c b/arch/arm/probes/kprobes/opt-arm.c
> index 6a60df3..f3bd1cc 100644
> --- a/arch/arm/probes/kprobes/opt-arm.c
> +++ b/arch/arm/probes/kprobes/opt-arm.c
> @@ -32,6 +32,13 @@
> #include "core.h"
>
> /*
> + * 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) & 0xc0000000UL))
I think you'd better define a macro for this bitmask.
> +
> +/*
> * 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"
> + " ldmia sp, {r13 - r15}\n"
Why this can't be a nop too?
Thank you,
> ".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 +263,24 @@ 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 register except pc.
> + */
> + code[TMPL_RESTORE_BEGIN] = __opcode_to_mem_arm(0xe89d7fff);
> + code[TMPL_RESTORE_ORIGN_INSN] = __opcode_to_mem_arm(orig->opcode);
> + 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@...achi.com
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