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The following patch adds the x86_64 architecture specific implementation
for function return probes.
Function return probes is a mechanism built on top of kprobes that allows
a caller to register a handler to be called when a given function exits.
For example, to instrument the return path of sys_mkdir:
static int sys_mkdir_exit(struct kretprobe_instance *i, struct pt_regs *regs)
{
printk("sys_mkdir exited\n");
return 0;
}
static struct kretprobe return_probe = {
.handler = sys_mkdir_exit,
};
<inside setup function>
return_probe.kp.addr = (kprobe_opcode_t *) kallsyms_lookup_name("sys_mkdir");
if (register_kretprobe(&return_probe)) {
printk(KERN_DEBUG "Unable to register return probe!\n");
/* do error path */
}
<inside cleanup function>
unregister_kretprobe(&return_probe);
The way this works is that:
* At system initialization time, kernel/kprobes.c installs a kprobe
on a function called kretprobe_trampoline() that is implemented in
the arch/x86_64/kernel/kprobes.c (More on this later)
* When a return probe is registered using register_kretprobe(),
kernel/kprobes.c will install a kprobe on the first instruction of the
targeted function with the pre handler set to arch_prepare_kretprobe()
which is implemented in arch/x86_64/kernel/kprobes.c.
* arch_prepare_kretprobe() will prepare a kretprobe instance that stores:
- nodes for hanging this instance in an empty or free list
- a pointer to the return probe
- the original return address
- a pointer to the stack address
With all this stowed away, arch_prepare_kretprobe() then sets the return
address for the targeted function to a special trampoline function called
kretprobe_trampoline() implemented in arch/x86_64/kernel/kprobes.c
* The kprobe completes as normal, with control passing back to the target
function that executes as normal, and eventually returns to our trampoline
function.
* Since a kprobe was installed on kretprobe_trampoline() during system
initialization, control passes back to kprobes via the architecture
specific function trampoline_probe_handler() which will lookup the
instance in an hlist maintained by kernel/kprobes.c, and then call
the handler function.
* When trampoline_probe_handler() is done, the kprobes infrastructure
single steps the original instruction (in this case just a top), and
then calls trampoline_post_handler(). trampoline_post_handler() then
looks up the instance again, puts the instance back on the free list,
and then makes a long jump back to the original return instruction.
So to recap, to instrument the exit path of a function this implementation
will cause four interruptions:
- A breakpoint at the very beginning of the function allowing us to
switch out the return address
- A single step interruption to execute the original instruction that
we replaced with the break instruction (normal kprobe flow)
- A breakpoint in the trampoline function where our instrumented function
returned to
- A single step interruption to execute the original instruction that
we replaced with the break instruction (normal kprobe flow)
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
66 lines
2.2 KiB
C
66 lines
2.2 KiB
C
#ifndef _ASM_KPROBES_H
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#define _ASM_KPROBES_H
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/*
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* Kernel Probes (KProbes)
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* include/asm-x86_64/kprobes.h
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright (C) IBM Corporation, 2002, 2004
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*
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* 2004-Oct Prasanna S Panchamukhi <prasanna@in.ibm.com> and Jim Keniston
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* kenistoj@us.ibm.com adopted from i386.
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*/
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#include <linux/types.h>
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#include <linux/ptrace.h>
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struct pt_regs;
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typedef u8 kprobe_opcode_t;
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#define BREAKPOINT_INSTRUCTION 0xcc
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#define MAX_INSN_SIZE 15
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#define MAX_STACK_SIZE 64
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#define MIN_STACK_SIZE(ADDR) (((MAX_STACK_SIZE) < \
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(((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR))) \
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? (MAX_STACK_SIZE) \
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: (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR)))
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#define JPROBE_ENTRY(pentry) (kprobe_opcode_t *)pentry
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#define ARCH_SUPPORTS_KRETPROBES
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void kretprobe_trampoline(void);
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/* Architecture specific copy of original instruction*/
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struct arch_specific_insn {
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/* copy of the original instruction */
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kprobe_opcode_t *insn;
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};
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/* trap3/1 are intr gates for kprobes. So, restore the status of IF,
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* if necessary, before executing the original int3/1 (trap) handler.
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*/
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static inline void restore_interrupts(struct pt_regs *regs)
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{
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if (regs->eflags & IF_MASK)
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local_irq_enable();
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}
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extern int post_kprobe_handler(struct pt_regs *regs);
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extern int kprobe_fault_handler(struct pt_regs *regs, int trapnr);
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extern int kprobe_handler(struct pt_regs *regs);
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extern int kprobe_exceptions_notify(struct notifier_block *self,
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unsigned long val, void *data);
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#endif /* _ASM_KPROBES_H */
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