[RFC PATCH] x86: kprobes: enable optmize relative call insn
Masami Hiramatsu
masami.hiramatsu.pt at hitachi.com
Sat Feb 7 02:08:04 PST 2015
(2015/02/06 19:30), Wang Nan wrote:
> In reply to Masami Hiramatsu's question on my previous early kprobe
> patch series at:
>
> http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/315771.html
>
> that on x86, early kprobe's applications range is limited by the type of
> optimizable instructions, I made this patch, which enables optimizing
> relative call instructions by introducing specific template for them.
> Such instructions make up about 7% of the kernel. In addition, when
> ftrace is enabled, funtion entry will be it, so early kprobe will be
> much useful than before.
Sorry, I couldn't understand this part. If you put kprobe on ftrace site
after ftrace enabled, it uses ftrace directly, instead of int3 or jump.
Anyway, ftrace-site instruction should be controlled by ftrace, not kprobes.
>
> The relationship between ftrace and kprobe is interesting. Under normal
> circumstances, kprobe utilizes ftrace. However, under early case,
> there's no way to tell whether the probing instruction is an ftrace
> entry. Another possible method on that is to move part of ftrace init
> ahead. However, to allow optimize more instructions should also be
> good for performance.
>
> Masami, I'd like to hear your reply on it. Do you think this patch is
> also useful for the normal cases?
Expanding "optimizability" is good, but I don't like add new asm-templates
which reduces maintainability less. Perhaps, we'd better start with reviewing
can_boost table again...
Thank you,
>
> Signed-off-by: Wang Nan <wangnan0 at huawei.com>
> ---
> arch/x86/include/asm/kprobes.h | 17 +++++++--
> arch/x86/kernel/kprobes/opt.c | 82 ++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 94 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h
> index 017f4bb..3627694 100644
> --- a/arch/x86/include/asm/kprobes.h
> +++ b/arch/x86/include/asm/kprobes.h
> @@ -31,6 +31,7 @@
> #define RELATIVEJUMP_OPCODE 0xe9
> #define RELATIVEJUMP_SIZE 5
> #define RELATIVECALL_OPCODE 0xe8
> +#define RELATIVECALL_SIZE 5
> #define RELATIVE_ADDR_SIZE 4
> #define MAX_STACK_SIZE 64
> #define MAX_OPTIMIZED_LENGTH (MAX_INSN_SIZE + RELATIVE_ADDR_SIZE)
> @@ -38,8 +39,10 @@
> #ifdef __ASSEMBLY__
>
> #define KPROBE_OPCODE_SIZE 1
> +#define OPT_CALL_TEMPLATE_SIZE (optprobe_call_template_end - \
> + optprobe_call_template_entry)
> #define MAX_OPTINSN_SIZE ((optprobe_template_end - optprobe_template_entry) + \
> - MAX_OPTIMIZED_LENGTH + RELATIVEJUMP_SIZE)
> + MAX_OPTIMIZED_LENGTH + RELATIVEJUMP_SIZE + OPT_CALL_TEMPLATE_SIZE)
>
> #ifdef CONFIG_EARLY_KPROBES
> # define EARLY_KPROBES_CODES_AREA \
> @@ -81,10 +84,20 @@ 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_call_template_entry;
> +extern __visible kprobe_opcode_t optprobe_call_template_val_destaddr;
> +extern __visible kprobe_opcode_t optprobe_call_template_val_retaddr;
> +extern __visible kprobe_opcode_t optprobe_call_template_end;
> +
> +#define OPT_CALL_TEMPLATE_SIZE \
> + ((unsigned long)&optprobe_call_template_end - \
> + (unsigned long)&optprobe_call_template_entry)
> #define MAX_OPTINSN_SIZE \
> (((unsigned long)&optprobe_template_end - \
> (unsigned long)&optprobe_template_entry) + \
> - MAX_OPTIMIZED_LENGTH + RELATIVEJUMP_SIZE)
> + MAX_OPTIMIZED_LENGTH + RELATIVEJUMP_SIZE + \
> + OPT_CALL_TEMPLATE_SIZE)
>
> extern const int kretprobe_blacklist_size;
>
> diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
> index dc5fccb..05dd06f 100644
> --- a/arch/x86/kernel/kprobes/opt.c
> +++ b/arch/x86/kernel/kprobes/opt.c
> @@ -39,6 +39,23 @@
>
> #include "common.h"
>
> +static inline bool
> +is_relcall(u8 *addr)
> +{
> + return (*(u8 *)(addr) == RELATIVECALL_OPCODE);
> +}
> +
> +static inline void *
> +get_relcall_target(u8 *addr)
> +{
> + struct __arch_relative_insn {
> + u8 op;
> + s32 raddr;
> + } __packed *insn;
> + insn = (struct __arch_relative_insn *)addr;
> + return (void *)((unsigned long)addr + RELATIVECALL_SIZE + insn->raddr);
> +}
> +
> unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
> {
> struct optimized_kprobe *op;
> @@ -89,6 +106,48 @@ static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
> }
>
> asm (
> +#ifdef CONFIG_X86_64
> + ".global optprobe_call_template_entry\n"
> + "optprobe_call_template_entry:"
> + "pushq %rdi\n"
> + ".global optprobe_call_template_val_destaddr\n"
> + "optprobe_call_template_val_destaddr:"
> + ASM_NOP5
> + ASM_NOP5
> + "pushq %rdi\n"
> + ".global optprobe_call_template_val_retaddr\n"
> + "optprobe_call_template_val_retaddr:"
> + ASM_NOP5
> + ASM_NOP5
> + "xchgq %rdi, 8(%rsp)\n"
> + "retq\n"
> +#else /* CONFIG_X86_32 */
> + ".global optprobe_call_template_entry\n"
> + "optprobe_call_template_entry:"
> + "push %edi\n"
> + ".global optprobe_call_template_val_destaddr\n"
> + "optprobe_call_template_val_destaddr:"
> + ASM_NOP5
> + "push %edi\n"
> + ".global optprobe_call_template_val_retaddr\n"
> + "optprobe_call_template_val_retaddr:"
> + ASM_NOP5
> + "xchg %edi, 4(%esp)\n"
> + "ret\n"
> +#endif
> + ".global optprobe_call_template_end\n"
> + "optprobe_call_template_end:\n"
> +);
> +
> +#define __OPTCALL_TMPL_MOVE_DESTADDR_IDX \
> + ((long)&optprobe_call_template_val_destaddr - (long)&optprobe_call_template_entry)
> +#define __OPTCALL_TMPL_MOVE_RETADDR_IDX \
> + ((long)&optprobe_call_template_val_retaddr - (long)&optprobe_call_template_entry)
> +#define __OPTCALL_TMPL_END_IDX \
> + ((long)&optprobe_call_template_end - (long)&optprobe_call_template_entry)
> +#define OPTCALL_TMPL_SIZE __OPTCALL_TMPL_END_IDX
> +
> +asm (
> ".global optprobe_template_entry\n"
> "optprobe_template_entry:\n"
> #ifdef CONFIG_X86_64
> @@ -135,6 +194,10 @@ asm (
> #define TMPL_END_IDX \
> ((long)&optprobe_template_end - (long)&optprobe_template_entry)
>
> +#define TMPL_OPTCALL_MOVE_DESTADDR_IDX (TMPL_END_IDX + __OPTCALL_TMPL_MOVE_DESTADDR_IDX)
> +#define TMPL_OPTCALL_MOVE_RETADDR_IDX (TMPL_END_IDX + __OPTCALL_TMPL_MOVE_RETADDR_IDX)
> +#define TMPL_OPTCALL_END_IDX (TMPL_END_IDX + __OPTCALL_TMPL_END_IDX)
> +
> #define INT3_SIZE sizeof(kprobe_opcode_t)
>
> /* Optimized kprobe call back function: called from optinsn */
> @@ -175,6 +238,12 @@ static int copy_optimized_instructions(u8 *dest, u8 *src)
> {
> int len = 0, ret;
>
> + if (is_relcall(src)) {
> + memcpy(dest, &optprobe_call_template_entry,
> + OPTCALL_TMPL_SIZE);
> + return OPTCALL_TMPL_SIZE;
> + }
> +
> while (len < RELATIVEJUMP_SIZE) {
> ret = __copy_instruction(dest + len, src + len);
> if (!ret || !can_boost(dest + len))
> @@ -365,9 +434,16 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
> /* Set probe function call */
> synthesize_relcall(buf + TMPL_CALL_IDX, optimized_callback);
>
> - /* Set returning jmp instruction at the tail of out-of-line buffer */
> - synthesize_reljump(buf + TMPL_END_IDX + op->optinsn.size,
> - (u8 *)op->kp.addr + op->optinsn.size);
> + if (!is_relcall(op->kp.addr)) {
> + /* Set returning jmp instruction at the tail of out-of-line buffer */
> + synthesize_reljump(buf + TMPL_END_IDX + op->optinsn.size,
> + (u8 *)op->kp.addr + op->optinsn.size);
> + } else {
> + synthesize_set_arg1(buf + TMPL_OPTCALL_MOVE_DESTADDR_IDX,
> + (unsigned long)(get_relcall_target(op->kp.addr)));
> + synthesize_set_arg1(buf + TMPL_OPTCALL_MOVE_RETADDR_IDX,
> + (unsigned long)(op->kp.addr + RELATIVECALL_SIZE));
> + }
>
> flush_icache_range((unsigned long) buf,
> (unsigned long) buf + TMPL_END_IDX +
>
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt at hitachi.com
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