Unverified Commit 829adda5 authored by Guo Ren's avatar Guo Ren Committed by Palmer Dabbelt
Browse files

riscv: Add KPROBES_ON_FTRACE supported 



This patch adds support for kprobes on ftrace call sites to avoids
much of the overhead with regular kprobes. Try it with simple
steps:

 echo 'p:myprobe sys_clone a0=%a0 a1=%a1 stack_val=+4($stack)' > /sys/kernel/de
bug/tracing/kprobe_events
 echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
 cat /sys/kernel/debug/tracing/trace
 tracer: nop

 entries-in-buffer/entries-written: 1/1   #P:1

                                _-----=> irqs-off
                               / _----=> need-resched
                              | / _---=> hardirq/softirq
                              || / _--=> preempt-depth
                              ||| /     delay
           TASK-PID     CPU#  ||||   TIMESTAMP  FUNCTION
              | |         |   ||||      |         |
              sh-92      [000] ....   369.899962: myprobe: (sys_clone+0x0/0x28) a0=0x1200011 a1=0x0 stack_val=0x201c20ffffffe0
 cat /sys/kernel/debug/kprobes/list
ffffffe00020b584  k  sys_clone+0x0    [FTRACE]
                                       ^^^^^^

Signed-off-by: default avatarGuo Ren <guoren@linux.alibaba.com>
Reviewed-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
parent c22b0bcb

arch/riscv/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -72,6 +72,7 @@ config RISCV 
	select HAVE_GENERIC_VDSO if MMU && 64BIT

	select HAVE_IRQ_TIME_ACCOUNTING

	select HAVE_KPROBES

	select HAVE_KPROBES_ON_FTRACE

	select HAVE_KRETPROBES

	select HAVE_PCI

	select HAVE_PERF_EVENTS

arch/riscv/kernel/probes/Makefile

+1 −0
Original line number Diff line number Diff line 
# SPDX-License-Identifier: GPL-2.0

obj-$(CONFIG_KPROBES)		+= kprobes.o decode-insn.o simulate-insn.o

obj-$(CONFIG_KPROBES)		+= kprobes_trampoline.o

obj-$(CONFIG_KPROBES_ON_FTRACE)	+= ftrace.o

CFLAGS_REMOVE_simulate-insn.o = $(CC_FLAGS_FTRACE)

arch/riscv/kernel/probes/ftrace.c

0 → 100644
+53 −0
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0



#include <linux/kprobes.h>



/* Ftrace callback handler for kprobes -- called under preepmt disabed */

void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,

			   struct ftrace_ops *ops, struct ftrace_regs *regs)

{

	struct kprobe *p;

	struct kprobe_ctlblk *kcb;



	p = get_kprobe((kprobe_opcode_t *)ip);

	if (unlikely(!p) || kprobe_disabled(p))

		return;



	kcb = get_kprobe_ctlblk();

	if (kprobe_running()) {

		kprobes_inc_nmissed_count(p);

	} else {

		unsigned long orig_ip = instruction_pointer(&(regs->regs));



		instruction_pointer_set(&(regs->regs), ip);



		__this_cpu_write(current_kprobe, p);

		kcb->kprobe_status = KPROBE_HIT_ACTIVE;

		if (!p->pre_handler || !p->pre_handler(p, &(regs->regs))) {

			/*

			 * Emulate singlestep (and also recover regs->pc)

			 * as if there is a nop

			 */

			instruction_pointer_set(&(regs->regs),

				(unsigned long)p->addr + MCOUNT_INSN_SIZE);

			if (unlikely(p->post_handler)) {

				kcb->kprobe_status = KPROBE_HIT_SSDONE;

				p->post_handler(p, &(regs->regs), 0);

			}

			instruction_pointer_set(&(regs->regs), orig_ip);

		}



		/*

		 * If pre_handler returns !0, it changes regs->pc. We have to

		 * skip emulating post_handler.

		 */

		__this_cpu_write(current_kprobe, NULL);

	}

}

NOKPROBE_SYMBOL(kprobe_ftrace_handler);



int arch_prepare_kprobe_ftrace(struct kprobe *p)

{

	p->ainsn.api.insn = NULL;

	return 0;

}