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Message-ID: <20060822053009.GC26279@in.ibm.com>
Date: Tue, 22 Aug 2006 11:00:09 +0530
From: Ananth N Mavinakayanahalli <ananth@...ibm.com>
To: lkml <linux-kernel@...r.kernel.org>
Cc: hch@...radead.org, Andrew Morton <akpm@...l.org>,
Prasanna S Panchamukhi <prasanna@...ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
Jim Keniston <jkenisto@...ibm.com>, davem@...emloft.net
Subject: [PATCH 3/3] Update Documentation/kprobes.txt
From: Ananth N Mavinakayanahalli <ananth@...ibm.com>
Documentation/kprobes.txt updated to reflect:
o In-kernel symbol resolution
o CONFIG_KALLSYMS dependency
o Usage of JPROBE_ENTRY
o Addition of return_value()
Also update the references list and usage examples to use correct module
interfaces.
---
Signed-off-by: Ananth N Mavinakayanahalli <ananth@...ibm.com>
Acked-by: Jim Keniston <jkenisto@...ibm.com>
---
Documentation/kprobes.txt | 89 ++++++++++++++++++++++++++++------------------
1 files changed, 56 insertions(+), 33 deletions(-)
Index: linux-2.6.18-rc4/Documentation/kprobes.txt
===================================================================
--- linux-2.6.18-rc4.orig/Documentation/kprobes.txt
+++ linux-2.6.18-rc4/Documentation/kprobes.txt
@@ -151,9 +151,9 @@ So that you can load and unload Kprobes-
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_handl
or during single-stepping of the probed instruction, Kprobes calls
kp->fault_handler. Any or all handlers can be NULL.
+NOTE:
+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
+transparently)
+
+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
+probepoint.
+
+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 func
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 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
#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, stru
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)
{
unregister_kprobe(&kp);
printk("kprobe unregistered\n");
}
+module_init(kprobe_init)
+module_exit(kprobe_exit)
MODULE_LICENSE("GPL");
----- 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,
}
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;
- my_jprobe.kp.addr = (kprobe_opcode_t *) kallsyms_lookup_name("do_fork");
- if (!my_jprobe.kp.addr) {
- printk("Couldn't find %s to plant jprobe\n", "do_fork");
- return -1;
- }
+ my_jprobe.kp.symbol_name = "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)
{
unregister_jprobe(&my_jprobe);
printk("jprobe unregistered\n");
}
+module_init(jprobe_init)
+module_exit(jprobe_exit)
MODULE_LICENSE("GPL");
----- 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 = 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;
- my_kretprobe.kp.addr =
- (kprobe_opcode_t *) kallsyms_lookup_name(probed_func);
- if (!my_kretprobe.kp.addr) {
- printk("Couldn't find %s to plant return probe\n", probed_func);
- return -1;
- }
+ 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;
@@ -569,7 +588,7 @@ int init_module(void)
return 0;
}
-void cleanup_module(void)
+static void __exit kretprobe_exit(void)
{
unregister_kretprobe(&my_kretprobe);
printk("kretprobe unregistered\n");
@@ -578,6 +597,8 @@ void cleanup_module(void)
my_kretprobe.nmissed, probed_func);
}
+module_init(kretprobe_init)
+module_exit(kretprobe_exit)
MODULE_LICENSE("GPL");
----- cut here -----
@@ -590,3 +611,5 @@ messages.)
For additional information on Kprobes, refer to the following URLs:
http://www-106.ibm.com/developerworks/library/l-kprobes.html?ca=dgr-lnxw42Kprobe
http://www.redhat.com/magazine/005mar05/features/kprobes/
+http://www-users.cs.umn.edu/~boutcher/kprobes/
+http://www.linuxsymposium.org/2006/linuxsymposium_procv2.pdf (pages 101-115)
-
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