uprobes/x86: Emulate push insns for uprobe on x86
Uprobe is a tracing mechanism for userspace programs. Typical uprobe will incur overhead of two traps. First trap is caused by replaced trap insn, and the second trap is to execute the original displaced insn in user space. To reduce the overhead, kernel provides hooks for architectures to emulate the original insn and skip the second trap. In x86, emulation is done for certain branch insns. This patch extends the emulation to "push <reg>" insns. These insns are typical in the beginning of the function. For example, bcc in https://github.com/iovisor/bcc repo provides tools to measure funclantency, detect memleak, etc. The tools will place uprobes in the beginning of function and possibly uretprobes at the end of function. This patch is able to reduce the trap overhead for uprobe from 2 to 1. Without this patch, uretprobe will typically incur three traps. With this patch, if the function starts with "push" insn, the number of traps can be reduced from 3 to 2. An experiment was conducted on two local VMs, fedora 26 64-bit VM and 32-bit VM, both 4 processors and 4GB memory, booted with latest tip repo (and this patch). The host is MacBook with intel i7 processor. The test program looks like: #include <stdio.h> #include <stdlib.h> #include <time.h> #include <sys/time.h> static void test() __attribute__((noinline)); void test() {} int main() { struct timeval start, end; gettimeofday(&start, NULL); for (int i = 0; i < 1000000; i++) { test(); } gettimeofday(&end, NULL); printf("%ld\n", ((end.tv_sec * 1000000 + end.tv_usec) - (start.tv_sec * 1000000 + start.tv_usec))); return 0; } The program is compiled without optimization, and the first insn for function "test" is "push %rbp". The host is relatively idle. Before the test run, the uprobe is inserted as below for uprobe: echo 'p <binary>:<test_func_offset>' > /sys/kernel/debug/tracing/uprobe_events echo 1 > /sys/kernel/debug/tracing/events/uprobes/enable and for uretprobe: echo 'r <binary>:<test_func_offset>' > /sys/kernel/debug/tracing/uprobe_events echo 1 > /sys/kernel/debug/tracing/events/uprobes/enable Unit: microsecond(usec) per loop iteration x86_64 W/ this patch W/O this patch uprobe 1.55 3.1 uretprobe 2.0 3.6 x86_32 W/ this patch W/O this patch uprobe 1.41 3.5 uretprobe 1.75 4.0 You can see that this patch significantly reduced the overhead, 50% for uprobe and 44% for uretprobe on x86_64, and even more on x86_32. Signed-off-by: Yonghong Song <yhs@fb.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-team@fb.com Link: http://lkml.kernel.org/r/20171201001202.3706564-1-yhs@fb.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Yonghong Song
Ingo Molnar
Родитель
d0300e5e8d
Коммит
e7ed9d9bd0
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@ -53,6 +53,10 @@ struct arch_uprobe {
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u8 fixups;
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u8 ilen;
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} defparam;
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struct {
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u8 reg_offset; /* to the start of pt_regs */
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u8 ilen;
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} push;
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};
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};
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@ -528,11 +528,11 @@ static int default_pre_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
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return 0;
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}
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static int push_ret_address(struct pt_regs *regs, unsigned long ip)
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static int emulate_push_stack(struct pt_regs *regs, unsigned long val)
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{
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unsigned long new_sp = regs->sp - sizeof_long();
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if (copy_to_user((void __user *)new_sp, &ip, sizeof_long()))
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if (copy_to_user((void __user *)new_sp, &val, sizeof_long()))
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return -EFAULT;
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regs->sp = new_sp;
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@ -566,7 +566,7 @@ static int default_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs
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regs->ip += correction;
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} else if (auprobe->defparam.fixups & UPROBE_FIX_CALL) {
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regs->sp += sizeof_long(); /* Pop incorrect return address */
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if (push_ret_address(regs, utask->vaddr + auprobe->defparam.ilen))
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if (emulate_push_stack(regs, utask->vaddr + auprobe->defparam.ilen))
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return -ERESTART;
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}
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/* popf; tell the caller to not touch TF */
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@ -655,7 +655,7 @@ static bool branch_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
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*
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* But there is corner case, see the comment in ->post_xol().
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*/
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if (push_ret_address(regs, new_ip))
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if (emulate_push_stack(regs, new_ip))
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return false;
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} else if (!check_jmp_cond(auprobe, regs)) {
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offs = 0;
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@ -665,6 +665,16 @@ static bool branch_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
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return true;
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}
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static bool push_emulate_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
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{
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unsigned long *src_ptr = (void *)regs + auprobe->push.reg_offset;
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if (emulate_push_stack(regs, *src_ptr))
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return false;
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regs->ip += auprobe->push.ilen;
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return true;
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}
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static int branch_post_xol_op(struct arch_uprobe *auprobe, struct pt_regs *regs)
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{
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BUG_ON(!branch_is_call(auprobe));
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@ -703,6 +713,10 @@ static const struct uprobe_xol_ops branch_xol_ops = {
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.post_xol = branch_post_xol_op,
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};
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static const struct uprobe_xol_ops push_xol_ops = {
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.emulate = push_emulate_op,
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};
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/* Returns -ENOSYS if branch_xol_ops doesn't handle this insn */
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static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
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{
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@ -750,6 +764,87 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
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return 0;
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}
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/* Returns -ENOSYS if push_xol_ops doesn't handle this insn */
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static int push_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
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{
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u8 opc1 = OPCODE1(insn), reg_offset = 0;
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if (opc1 < 0x50 || opc1 > 0x57)
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return -ENOSYS;
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if (insn->length > 2)
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return -ENOSYS;
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if (insn->length == 2) {
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/* only support rex_prefix 0x41 (x64 only) */
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#ifdef CONFIG_X86_64
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if (insn->rex_prefix.nbytes != 1 ||
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insn->rex_prefix.bytes[0] != 0x41)
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return -ENOSYS;
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switch (opc1) {
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case 0x50:
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reg_offset = offsetof(struct pt_regs, r8);
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break;
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case 0x51:
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reg_offset = offsetof(struct pt_regs, r9);
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break;
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case 0x52:
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reg_offset = offsetof(struct pt_regs, r10);
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break;
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case 0x53:
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reg_offset = offsetof(struct pt_regs, r11);
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break;
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case 0x54:
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reg_offset = offsetof(struct pt_regs, r12);
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break;
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case 0x55:
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reg_offset = offsetof(struct pt_regs, r13);
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break;
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case 0x56:
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reg_offset = offsetof(struct pt_regs, r14);
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break;
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case 0x57:
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reg_offset = offsetof(struct pt_regs, r15);
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break;
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}
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#else
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return -ENOSYS;
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#endif
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} else {
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switch (opc1) {
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case 0x50:
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reg_offset = offsetof(struct pt_regs, ax);
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break;
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case 0x51:
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reg_offset = offsetof(struct pt_regs, cx);
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break;
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case 0x52:
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reg_offset = offsetof(struct pt_regs, dx);
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break;
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case 0x53:
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reg_offset = offsetof(struct pt_regs, bx);
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break;
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case 0x54:
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reg_offset = offsetof(struct pt_regs, sp);
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break;
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case 0x55:
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reg_offset = offsetof(struct pt_regs, bp);
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break;
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case 0x56:
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reg_offset = offsetof(struct pt_regs, si);
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break;
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case 0x57:
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reg_offset = offsetof(struct pt_regs, di);
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break;
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}
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}
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auprobe->push.reg_offset = reg_offset;
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auprobe->push.ilen = insn->length;
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auprobe->ops = &push_xol_ops;
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return 0;
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}
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/**
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* arch_uprobe_analyze_insn - instruction analysis including validity and fixups.
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* @mm: the probed address space.
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@ -771,6 +866,10 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe, struct mm_struct *mm,
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if (ret != -ENOSYS)
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return ret;
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ret = push_setup_xol_ops(auprobe, &insn);
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if (ret != -ENOSYS)
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return ret;
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/*
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* Figure out which fixups default_post_xol_op() will need to perform,
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* and annotate defparam->fixups accordingly.
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