the probe is to be inserted and what handler is to be called when
the probe is hit.
+There are also register_/unregister_*probes() functions for batch
+registration/unregistration of a group of *probes. These functions
+can speed up unregistration process when you have to unregister
+a lot of probes at once.
+
The next three subsections explain how the different types of
probes work. They explain certain things that you'll need to
know in order to make the best use of Kprobes -- e.g., the
- ia64 (Does not support probes on instruction slot1.)
- sparc64 (Return probes not yet implemented.)
- arm
+- ppc
3. Configuring Kprobes
4. API Reference
The Kprobes API includes a "register" function and an "unregister"
-function for each type of probe. Here are terse, mini-man-page
-specifications for these functions and the associated probe handlers
-that you'll write. See the latter half of this document for examples.
+function for each type of probe. The API also includes "register_*probes"
+and "unregister_*probes" functions for (un)registering arrays of probes.
+Here are terse, mini-man-page specifications for these functions and
+the associated probe handlers that you'll write. See the files in the
+samples/kprobes/ sub-directory for examples.
4.1 register_kprobe
is single-stepped, Kprobe calls kp->post_handler. If a fault
occurs during execution of kp->pre_handler or kp->post_handler,
or during single-stepping of the probed instruction, Kprobes calls
-kp->fault_handler. Any or all handlers can be NULL.
+kp->fault_handler. Any or all handlers can be NULL. If kp->flags
+is set KPROBE_FLAG_DISABLED, that kp will be registered but disabled,
+so, it's handlers aren't hit until calling enable_kprobe(kp).
NOTE:
1. With the introduction of the "symbol_name" field to struct kprobe,
Removes the specified probe. The unregister function can be called
at any time after the probe has been registered.
+NOTE:
+If the functions find an incorrect probe (ex. an unregistered probe),
+they clear the addr field of the probe.
+
+4.5 register_*probes
+
+#include <linux/kprobes.h>
+int register_kprobes(struct kprobe **kps, int num);
+int register_kretprobes(struct kretprobe **rps, int num);
+int register_jprobes(struct jprobe **jps, int num);
+
+Registers each of the num probes in the specified array. If any
+error occurs during registration, all probes in the array, up to
+the bad probe, are safely unregistered before the register_*probes
+function returns.
+- kps/rps/jps: an array of pointers to *probe data structures
+- num: the number of the array entries.
+
+NOTE:
+You have to allocate(or define) an array of pointers and set all
+of the array entries before using these functions.
+
+4.6 unregister_*probes
+
+#include <linux/kprobes.h>
+void unregister_kprobes(struct kprobe **kps, int num);
+void unregister_kretprobes(struct kretprobe **rps, int num);
+void unregister_jprobes(struct jprobe **jps, int num);
+
+Removes each of the num probes in the specified array at once.
+
+NOTE:
+If the functions find some incorrect probes (ex. unregistered
+probes) in the specified array, they clear the addr field of those
+incorrect probes. However, other probes in the array are
+unregistered correctly.
+
+4.7 disable_*probe
+
+#include <linux/kprobes.h>
+int disable_kprobe(struct kprobe *kp);
+int disable_kretprobe(struct kretprobe *rp);
+int disable_jprobe(struct jprobe *jp);
+
+Temporarily disables the specified *probe. You can enable it again by using
+enable_*probe(). You must specify the probe which has been registered.
+
+4.8 enable_*probe
+
+#include <linux/kprobes.h>
+int enable_kprobe(struct kprobe *kp);
+int enable_kretprobe(struct kretprobe *rp);
+int enable_jprobe(struct jprobe *jp);
+
+Enables *probe which has been disabled by disable_*probe(). You must specify
+the probe which has been registered.
+
5. Kprobes Features and Limitations
Kprobes allows multiple probes at the same address. Currently,
8. Kprobes Example
-Here's a sample kernel module showing the use of kprobes to dump a
-stack trace and selected i386 registers when do_fork() is called.
------ cut here -----
-/*kprobe_example.c*/
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/kprobes.h>
-#include <linux/sched.h>
-
-/*For each probe you need to allocate a kprobe structure*/
-static struct kprobe kp;
-
-/*kprobe pre_handler: called just before the probed instruction is executed*/
-int handler_pre(struct kprobe *p, struct pt_regs *regs)
-{
- printk("pre_handler: p->addr=0x%p, eip=%lx, eflags=0x%lx\n",
- p->addr, regs->eip, regs->eflags);
- dump_stack();
- return 0;
-}
-
-/*kprobe post_handler: called after the probed instruction is executed*/
-void handler_post(struct kprobe *p, struct pt_regs *regs, unsigned long flags)
-{
- printk("post_handler: p->addr=0x%p, eflags=0x%lx\n",
- p->addr, regs->eflags);
-}
-
-/* fault_handler: this is called if an exception is generated for any
- * instruction within the pre- or post-handler, or when Kprobes
- * single-steps the probed instruction.
- */
-int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
-{
- printk("fault_handler: p->addr=0x%p, trap #%dn",
- p->addr, trapnr);
- /* Return 0 because we don't handle the fault. */
- return 0;
-}
-
-static int __init kprobe_init(void)
-{
- int ret;
- kp.pre_handler = handler_pre;
- kp.post_handler = handler_post;
- kp.fault_handler = handler_fault;
- kp.symbol_name = "do_fork";
-
- ret = register_kprobe(&kp);
- if (ret < 0) {
- printk("register_kprobe failed, returned %d\n", ret);
- return ret;
- }
- printk("kprobe registered\n");
- return 0;
-}
-
-static void __exit kprobe_exit(void)
-{
- unregister_kprobe(&kp);
- printk("kprobe unregistered\n");
-}
-
-module_init(kprobe_init)
-module_exit(kprobe_exit)
-MODULE_LICENSE("GPL");
------ cut here -----
-
-You can build the kernel module, kprobe-example.ko, using the following
-Makefile:
------ cut here -----
-obj-m := kprobe-example.o
-KDIR := /lib/modules/$(shell uname -r)/build
-PWD := $(shell pwd)
-default:
- $(MAKE) -C $(KDIR) SUBDIRS=$(PWD) modules
-clean:
- rm -f *.mod.c *.ko *.o
------ cut here -----
-
-$ make
-$ su -
-...
-# insmod kprobe-example.ko
-
-You will see the trace data in /var/log/messages and on the console
-whenever do_fork() is invoked to create a new process.
+See samples/kprobes/kprobe_example.c
9. Jprobes Example
-Here's a sample kernel module showing the use of jprobes to dump
-the arguments of do_fork().
------ cut here -----
-/*jprobe-example.c */
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/fs.h>
-#include <linux/uio.h>
-#include <linux/kprobes.h>
-
-/*
- * Jumper probe for do_fork.
- * Mirror principle enables access to arguments of the probed routine
- * from the probe handler.
- */
-
-/* Proxy routine having the same arguments as actual do_fork() routine */
-long jdo_fork(unsigned long clone_flags, unsigned long stack_start,
- struct pt_regs *regs, unsigned long stack_size,
- int __user * parent_tidptr, int __user * child_tidptr)
-{
- printk("jprobe: clone_flags=0x%lx, stack_size=0x%lx, regs=0x%p\n",
- clone_flags, stack_size, regs);
- /* Always end with a call to jprobe_return(). */
- jprobe_return();
- /*NOTREACHED*/
- return 0;
-}
-
-static struct jprobe my_jprobe = {
- .entry = jdo_fork
-};
-
-static int __init jprobe_init(void)
-{
- int ret;
- my_jprobe.kp.symbol_name = "do_fork";
-
- if ((ret = register_jprobe(&my_jprobe)) <0) {
- printk("register_jprobe failed, returned %d\n", ret);
- return -1;
- }
- printk("Planted jprobe at %p, handler addr %p\n",
- my_jprobe.kp.addr, my_jprobe.entry);
- return 0;
-}
-
-static void __exit jprobe_exit(void)
-{
- unregister_jprobe(&my_jprobe);
- printk("jprobe unregistered\n");
-}
-
-module_init(jprobe_init)
-module_exit(jprobe_exit)
-MODULE_LICENSE("GPL");
------ cut here -----
-
-Build and insert the kernel module as shown in the above kprobe
-example. You will see the trace data in /var/log/messages and on
-the console whenever do_fork() is invoked to create a new process.
-(Some messages may be suppressed if syslogd is configured to
-eliminate duplicate messages.)
+See samples/kprobes/jprobe_example.c
10. Kretprobes Example
-Here's a sample kernel module showing the use of return probes to
-report failed calls to sys_open().
------ cut here -----
-/*kretprobe-example.c*/
-#include <linux/kernel.h>
-#include <linux/module.h>
-#include <linux/kprobes.h>
-#include <linux/ktime.h>
-
-/* per-instance private data */
-struct my_data {
- ktime_t entry_stamp;
-};
-
-static const char *probed_func = "sys_open";
-
-/* Timestamp function entry. */
-static int entry_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
-{
- struct my_data *data;
-
- if(!current->mm)
- return 1; /* skip kernel threads */
-
- data = (struct my_data *)ri->data;
- data->entry_stamp = ktime_get();
- return 0;
-}
-
-/* If the probed function failed, log the return value and duration.
- * Duration may turn out to be zero consistently, depending upon the
- * granularity of time accounting on the platform. */
-static int return_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
-{
- int retval = regs_return_value(regs);
- struct my_data *data = (struct my_data *)ri->data;
- s64 delta;
- ktime_t now;
-
- if (retval < 0) {
- now = ktime_get();
- delta = ktime_to_ns(ktime_sub(now, data->entry_stamp));
- printk("%s: return val = %d (duration = %lld ns)\n",
- probed_func, retval, delta);
- }
- return 0;
-}
-
-static struct kretprobe my_kretprobe = {
- .handler = return_handler,
- .entry_handler = entry_handler,
- .data_size = sizeof(struct my_data),
- .maxactive = 20, /* probe up to 20 instances concurrently */
-};
-
-static int __init kretprobe_init(void)
-{
- int ret;
- my_kretprobe.kp.symbol_name = (char *)probed_func;
-
- if ((ret = register_kretprobe(&my_kretprobe)) < 0) {
- printk("register_kretprobe failed, returned %d\n", ret);
- return -1;
- }
- printk("Kretprobe active on %s\n", my_kretprobe.kp.symbol_name);
- return 0;
-}
-
-static void __exit kretprobe_exit(void)
-{
- unregister_kretprobe(&my_kretprobe);
- printk("kretprobe unregistered\n");
- /* nmissed > 0 suggests that maxactive was set too low. */
- printk("Missed probing %d instances of %s\n",
- my_kretprobe.nmissed, probed_func);
-}
-
-module_init(kretprobe_init)
-module_exit(kretprobe_exit)
-MODULE_LICENSE("GPL");
------ cut here -----
-
-Build and insert the kernel module as shown in the above kprobe
-example. You will see the trace data in /var/log/messages and on the
-console whenever sys_open() returns a negative value. (Some messages
-may be suppressed if syslogd is configured to eliminate duplicate
-messages.)
+See samples/kprobes/kretprobe_example.c
For additional information on Kprobes, refer to the following URLs:
http://www-106.ibm.com/developerworks/library/l-kprobes.html?ca=dgr-lnxw42Kprobe
Appendix A: The kprobes debugfs interface
With recent kernels (> 2.6.20) the list of registered kprobes is visible
-under the /debug/kprobes/ directory (assuming debugfs is mounted at /debug).
+under the /sys/kernel/debug/kprobes/ directory (assuming debugfs is mounted at //sys/kernel/debug).
-/debug/kprobes/list: Lists all registered probes on the system
+/sys/kernel/debug/kprobes/list: Lists all registered probes on the system
c015d71a k vfs_read+0x0
c011a316 j do_fork+0x0
The second column identifies the type of probe (k - kprobe, r - kretprobe
and j - jprobe), while the third column specifies the symbol+offset of
the probe. If the probed function belongs to a module, the module name
-is also specified.
-
-/debug/kprobes/enabled: Turn kprobes ON/OFF
-
-Provides a knob to globally turn registered kprobes ON or OFF. By default,
-all kprobes are enabled. By echoing "0" to this file, all registered probes
-will be disarmed, till such time a "1" is echoed to this file.
+is also specified. Following columns show probe status. If the probe is on
+a virtual address that is no longer valid (module init sections, module
+virtual addresses that correspond to modules that've been unloaded),
+such probes are marked with [GONE]. If the probe is temporarily disabled,
+such probes are marked with [DISABLED].
+
+/sys/kernel/debug/kprobes/enabled: Turn kprobes ON/OFF forcibly.
+
+Provides a knob to globally and forcibly turn registered kprobes ON or OFF.
+By default, all kprobes are enabled. By echoing "0" to this file, all
+registered probes will be disarmed, till such time a "1" is echoed to this
+file. Note that this knob just disarms and arms all kprobes and doesn't
+change each probe's disabling state. This means that disabled kprobes (marked
+[DISABLED]) will be not enabled if you turn ON all kprobes by this knob.
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff