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authorRusty Lynch <rusty.lynch@intel.com>2005-06-23 00:09:23 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-06-23 09:45:21 -0700
commit73649dab0fd524cb8545a8cb83c6eaf77b107105 (patch)
tree70f43b37ba915de148c28008e275dacec200e33f /include/asm-x86_64
parentb94cce926b2b902b79380ccba370d6f9f2980de0 (diff)
downloadlinux-73649dab0fd524cb8545a8cb83c6eaf77b107105.tar.gz
[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/asm-x86_64')
-rw-r--r--include/asm-x86_64/kprobes.h3
1 files changed, 3 insertions, 0 deletions
diff --git a/include/asm-x86_64/kprobes.h b/include/asm-x86_64/kprobes.h
index bfea52d516f..6d6d883fdf6 100644
--- a/include/asm-x86_64/kprobes.h
+++ b/include/asm-x86_64/kprobes.h
@@ -38,6 +38,9 @@ typedef u8 kprobe_opcode_t;
: (((unsigned long)current_thread_info()) + THREAD_SIZE - (ADDR)))
#define JPROBE_ENTRY(pentry) (kprobe_opcode_t *)pentry
+#define ARCH_SUPPORTS_KRETPROBES
+
+void kretprobe_trampoline(void);
/* Architecture specific copy of original instruction*/
struct arch_specific_insn {