Commit 09b18203 authored by Ananth N Mavinakayanahalli's avatar Ananth N Mavinakayanahalli Committed by Linus Torvalds
Browse files

[PATCH] Update Documentation/kprobes.txt

Documentation/kprobes.txt updated to reflect:

o In-kernel symbol resolution
o CONFIG_KALLSYMS dependency
o Addition of regs_return_value()

Also update the references list and usage examples to use correct module
Signed-off-by: default avatarAnanth N Mavinakayanahalli <>
Acked-by: default avatarJim Keniston <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent b3f827cb
......@@ -151,9 +151,9 @@ So that you can load and unload Kprobes-based instrumentation modules,
make sure "Loadable module support" (CONFIG_MODULES) and "Module
unloading" (CONFIG_MODULE_UNLOAD) are set to "y".
You may also want to ensure that CONFIG_KALLSYMS and perhaps even
CONFIG_KALLSYMS_ALL are set to "y", since kallsyms_lookup_name()
is a handy, version-independent way to find a function's address.
Also make sure that CONFIG_KALLSYMS and perhaps even CONFIG_KALLSYMS_ALL
are set to "y", since kallsyms_lookup_name() is used by the in-kernel
kprobe address resolution code.
If you need to insert a probe in the middle of a function, you may find
it useful to "Compile the kernel with debug info" (CONFIG_DEBUG_INFO),
......@@ -179,6 +179,27 @@ 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.
1. With the introduction of the "symbol_name" field to struct kprobe,
the probepoint address resolution will now be taken care of by the kernel.
The following will now work:
kp.symbol_name = "symbol_name";
(64-bit powerpc intricacies such as function descriptors are handled
2. Use the "offset" field of struct kprobe if the offset into the symbol
to install a probepoint is known. This field is used to calculate the
3. Specify either the kprobe "symbol_name" OR the "addr". If both are
specified, kprobe registration will fail with -EINVAL.
4. With CISC architectures (such as i386 and x86_64), the kprobes code
does not validate if the kprobe.addr is at an instruction boundary.
Use "offset" with caution.
register_kprobe() returns 0 on success, or a negative errno otherwise.
User's pre-handler (kp->pre_handler):
......@@ -225,6 +246,12 @@ control to Kprobes.) If the probed function is declared asmlinkage,
fastcall, or anything else that affects how args are passed, the
handler's declaration must match.
NOTE: A macro JPROBE_ENTRY is provided to handle architecture-specific
aliasing of jp->entry. In the interest of portability, it is advised
to use:
jp->entry = JPROBE_ENTRY(handler);
register_jprobe() returns 0 on success, or a negative errno otherwise.
4.3 register_kretprobe
......@@ -251,6 +278,11 @@ of interest:
- ret_addr: the return address
- rp: points to the corresponding kretprobe object
- task: points to the corresponding task struct
The regs_return_value(regs) macro provides a simple abstraction to
extract the return value from the appropriate register as defined by
the architecture's ABI.
The handler's return value is currently ignored.
4.4 unregister_*probe
......@@ -369,7 +401,6 @@ stack trace and selected i386 registers when do_fork() is called.
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/kallsyms.h>
#include <linux/sched.h>
/*For each probe you need to allocate a kprobe structure*/
......@@ -403,18 +434,14 @@ int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
return 0;
int init_module(void)
static int __init kprobe_init(void)
int ret;
kp.pre_handler = handler_pre;
kp.post_handler = handler_post;
kp.fault_handler = handler_fault;
kp.addr = (kprobe_opcode_t*) kallsyms_lookup_name("do_fork");
/* register the kprobe now */
if (!kp.addr) {
printk("Couldn't find %s to plant kprobe\n", "do_fork");
return -1;
kp.symbol_name = "do_fork";
if ((ret = register_kprobe(&kp) < 0)) {
printk("register_kprobe failed, returned %d\n", ret);
return -1;
......@@ -423,12 +450,14 @@ int init_module(void)
return 0;
void cleanup_module(void)
static void __exit kprobe_exit(void)
printk("kprobe unregistered\n");
----- cut here -----
......@@ -463,7 +492,6 @@ the arguments of do_fork().
#include <linux/fs.h>
#include <linux/uio.h>
#include <linux/kprobes.h>
#include <linux/kallsyms.h>
* Jumper probe for do_fork.
......@@ -485,17 +513,13 @@ long jdo_fork(unsigned long clone_flags, unsigned long stack_start,
static struct jprobe my_jprobe = {
.entry = (kprobe_opcode_t *) jdo_fork
.entry = JPROBE_ENTRY(jdo_fork)
int init_module(void)
static int __init jprobe_init(void)
int ret; = (kprobe_opcode_t *) kallsyms_lookup_name("do_fork");
if (! {
printk("Couldn't find %s to plant jprobe\n", "do_fork");
return -1;
} = "do_fork";
if ((ret = register_jprobe(&my_jprobe)) <0) {
printk("register_jprobe failed, returned %d\n", ret);
......@@ -506,12 +530,14 @@ int init_module(void)
return 0;
void cleanup_module(void)
static void __exit jprobe_exit(void)
printk("jprobe unregistered\n");
----- cut here -----
......@@ -530,16 +556,13 @@ report failed calls to sys_open().
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/kallsyms.h>
static const char *probed_func = "sys_open";
/* Return-probe handler: If the probed function fails, log the return value. */
static int ret_handler(struct kretprobe_instance *ri, struct pt_regs *regs)
// Substitute the appropriate register name for your architecture --
// e.g., regs->rax for x86_64, regs->gpr[3] for ppc64.
int retval = (int) regs->eax;
int retval = regs_return_value(regs);
if (retval < 0) {
printk("%s returns %d\n", probed_func, retval);
......@@ -552,15 +575,11 @@ static struct kretprobe my_kretprobe = {
.maxactive = 20
int init_module(void)
static int __init kretprobe_init(void)
int ret; =
(kprobe_opcode_t *) kallsyms_lookup_name(probed_func);
if (! {
printk("Couldn't find %s to plant return probe\n", probed_func);
return -1;
} = (char *)probed_func;
if ((ret = register_kretprobe(&my_kretprobe)) < 0) {
printk("register_kretprobe failed, returned %d\n", ret);
return -1;
......@@ -569,7 +588,7 @@ int init_module(void)
return 0;
void cleanup_module(void)
static void __exit kretprobe_exit(void)
printk("kretprobe unregistered\n");
......@@ -578,6 +597,8 @@ void cleanup_module(void)
my_kretprobe.nmissed, probed_func);
----- cut here -----
......@@ -590,3 +611,5 @@ messages.)
For additional information on Kprobes, refer to the following URLs: (pages 101-115)
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment