diff options
author | Rusty Lynch <rusty.lynch@intel.com> | 2005-06-23 03:09:23 -0400 |
---|---|---|
committer | Linus Torvalds <torvalds@ppc970.osdl.org> | 2005-06-23 12:45:21 -0400 |
commit | 73649dab0fd524cb8545a8cb83c6eaf77b107105 (patch) | |
tree | 70f43b37ba915de148c28008e275dacec200e33f /include | |
parent | b94cce926b2b902b79380ccba370d6f9f2980de0 (diff) |
[PATCH] x86_64 specific function return probes
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>
Diffstat (limited to 'include')
-rw-r--r-- | include/asm-x86_64/kprobes.h | 3 |
1 files changed, 3 insertions, 0 deletions
diff --git a/include/asm-x86_64/kprobes.h b/include/asm-x86_64/kprobes.h index bfea52d516f8..6d6d883fdf6d 100644 --- a/include/asm-x86_64/kprobes.h +++ b/include/asm-x86_64/kprobes.h | |||
@@ -38,6 +38,9 @@ typedef u8 kprobe_opcode_t; | |||
38 | : (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR))) | 38 | : (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR))) |
39 | 39 | ||
40 | #define JPROBE_ENTRY(pentry) (kprobe_opcode_t *)pentry | 40 | #define JPROBE_ENTRY(pentry) (kprobe_opcode_t *)pentry |
41 | #define ARCH_SUPPORTS_KRETPROBES | ||
42 | |||
43 | void kretprobe_trampoline(void); | ||
41 | 44 | ||
42 | /* Architecture specific copy of original instruction*/ | 45 | /* Architecture specific copy of original instruction*/ |
43 | struct arch_specific_insn { | 46 | struct arch_specific_insn { |