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riscv: Add KPROBES_ON_FTRACE supported

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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: Guo Ren <guoren@linux.alibaba.com>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
This commit is contained in:
Guo Ren 2020-12-17 16:01:43 +00:00 committed by Palmer Dabbelt
parent c22b0bcb1d
commit 829adda597
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GPG Key ID: 2E1319F35FBB1889
3 changed files with 55 additions and 0 deletions
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1
arch/riscv/Kconfig
View File

@ -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

1
arch/riscv/kernel/probes/Makefile
View File

@ -1,4 +1,5 @@
# 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)

53
arch/riscv/kernel/probes/ftrace.c Normal file
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@ -0,0 +1,53 @@
// 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;
}