Merge ../linus

[linux-drm-fsl-dcu.git] / Documentation / kprobes.txt

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 0541fe1de70482e74fa2f10c409130b1ac21ef4b..d71fafffce90de81cba916c5d98dae7db5e9eb63 100644 (file)
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -136,21 +136,24 @@ Kprobes, jprobes, and return probes are implemented on the following
 architectures:
 
 - i386
 architectures:
 
 - i386

-- x86_64 (AMD-64, E64MT)
+- x86_64 (AMD-64, EM64T)

 - ppc64
 - ppc64

-- ia64 (Support for probes on certain instruction types is still in progress.)
+- ia64 (Does not support probes on instruction slot1.)

 - sparc64 (Return probes not yet implemented.)
 
 3. Configuring Kprobes
 
 When configuring the kernel using make menuconfig/xconfig/oldconfig,
 - sparc64 (Return probes not yet implemented.)
 
 3. Configuring Kprobes
 
 When configuring the kernel using make menuconfig/xconfig/oldconfig,

-ensure that CONFIG_KPROBES is set to "y".  Under "Kernel hacking",
-look for "Kprobes".  You may have to enable "Kernel debugging"
-(CONFIG_DEBUG_KERNEL) before you can enable Kprobes.
+ensure that CONFIG_KPROBES is set to "y".  Under "Instrumentation
+Support", look for "Kprobes".

 
 

-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.
+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".
+
+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),
 
 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),


@@ -176,6 +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.
 
 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):
 register_kprobe() returns 0 on success, or a negative errno otherwise.
 
 User's pre-handler (kp->pre_handler):


@@ -222,6 +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.
 
 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
 register_jprobe() returns 0 on success, or a negative errno otherwise.
 
 4.3 register_kretprobe


@@ -248,6 +278,11 @@ of interest:
 - ret_addr: the return address
 - rp: points to the corresponding kretprobe object
 - task: points to the corresponding task struct
 - 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
 The handler's return value is currently ignored.
 
 4.4 unregister_*probe


@@ -262,18 +297,18 @@ at any time after the probe has been registered.
 
 5. Kprobes Features and Limitations
 
 
 5. Kprobes Features and Limitations
 

-As of Linux v2.6.12, Kprobes allows multiple probes at the same
-address.  Currently, however, there cannot be multiple jprobes on
-the same function at the same time.
+Kprobes allows multiple probes at the same address.  Currently,
+however, there cannot be multiple jprobes on the same function at
+the same time.

 
 In general, you can install a probe anywhere in the kernel.
 In particular, you can probe interrupt handlers.  Known exceptions
 are discussed in this section.
 
 
 In general, you can install a probe anywhere in the kernel.
 In particular, you can probe interrupt handlers.  Known exceptions
 are discussed in this section.
 

-For obvious reasons, it's a bad idea to install a probe in
-the code that implements Kprobes (mostly kernel/kprobes.c and
-arch/*/kernel/kprobes.c).  A patch in the v2.6.13 timeframe instructs
-Kprobes to reject such requests.
+The register_*probe functions will return -EINVAL if you attempt
+to install a probe in the code that implements Kprobes (mostly
+kernel/kprobes.c and arch/*/kernel/kprobes.c, but also functions such
+as do_page_fault and notifier_call_chain).

 
 If you install a probe in an inline-able function, Kprobes makes
 no attempt to chase down all inline instances of the function and
 
 If you install a probe in an inline-able function, Kprobes makes
 no attempt to chase down all inline instances of the function and


@@ -290,18 +325,14 @@ from the accidental ones.  Don't drink and probe.
 
 Kprobes makes no attempt to prevent probe handlers from stepping on
 each other -- e.g., probing printk() and then calling printk() from a
 
 Kprobes makes no attempt to prevent probe handlers from stepping on
 each other -- e.g., probing printk() and then calling printk() from a

-probe handler.  As of Linux v2.6.12, if a probe handler hits a probe,
-that second probe's handlers won't be run in that instance.
-
-In Linux v2.6.12 and previous versions, Kprobes' data structures are
-protected by a single lock that is held during probe registration and
-unregistration and while handlers are run.  Thus, no two handlers
-can run simultaneously.  To improve scalability on SMP systems,
-this restriction will probably be removed soon, in which case
-multiple handlers (or multiple instances of the same handler) may
-run concurrently on different CPUs.  Code your handlers accordingly.
-
-Kprobes does not use semaphores or allocate memory except during
+probe handler.  If a probe handler hits a probe, that second probe's
+handlers won't be run in that instance, and the kprobe.nmissed member
+of the second probe will be incremented.
+
+As of Linux v2.6.15-rc1, multiple handlers (or multiple instances of
+the same handler) may run concurrently on different CPUs.
+
+Kprobes does not use mutexes or allocate memory except during

 registration and unregistration.
 
 Probe handlers are run with preemption disabled.  Depending on the
 registration and unregistration.
 
 Probe handlers are run with preemption disabled.  Depending on the


@@ -316,11 +347,18 @@ address instead of the real return address for kretprobed functions.
 (As far as we can tell, __builtin_return_address() is used only
 for instrumentation and error reporting.)
 
 (As far as we can tell, __builtin_return_address() is used only
 for instrumentation and error reporting.)
 

-If the number of times a function is called does not match the
-number of times it returns, registering a return probe on that
-function may produce undesirable results.  We have the do_exit()
-and do_execve() cases covered.  do_fork() is not an issue.  We're
-unaware of other specific cases where this could be a problem.
+If the number of times a function is called does not match the number
+of times it returns, registering a return probe on that function may
+produce undesirable results.  We have the do_exit() case covered.
+do_execve() and do_fork() are not an issue.  We're unaware of other
+specific cases where this could be a problem.
+
+If, upon entry to or exit from a function, the CPU is running on
+a stack other than that of the current task, registering a return
+probe on that function may produce undesirable results.  For this
+reason, Kprobes doesn't support return probes (or kprobes or jprobes)
+on the x86_64 version of __switch_to(); the registration functions
+return -EINVAL.

 
 6. Probe Overhead
 
 
 6. Probe Overhead
 


@@ -347,14 +385,12 @@ k = 0.77 usec; j = 1.31; r = 1.26; kr = 1.45; jr = 1.99
 
 7. TODO
 
 
 7. TODO
 

-a. SystemTap (http://sourceware.org/systemtap): Work in progress
-to provide a simplified programming interface for probe-based
-instrumentation.
-b. Improved SMP scalability: Currently, work is in progress to handle
-multiple kprobes in parallel.
-c. Kernel return probes for sparc64.
-d. Support for other architectures.
-e. User-space probes.
+a. SystemTap (http://sourceware.org/systemtap): Provides a simplified
+programming interface for probe-based instrumentation.  Try it out.
+b. Kernel return probes for sparc64.
+c. Support for other architectures.
+d. User-space probes.
+e. Watchpoint probes (which fire on data references).

 
 8. Kprobes Example
 
 
 8. Kprobes Example
 


@@ -365,7 +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/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*/
 #include <linux/sched.h>
 
 /*For each probe you need to allocate a kprobe structure*/


@@ -399,32 +434,31 @@ int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
        return 0;
 }
 
        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;
 {
        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;
-       }
-       if ((ret = register_kprobe(&kp) < 0)) {
+       kp.symbol_name = "do_fork";
+
+       ret = register_kprobe(&kp);
+       if (ret < 0) {

                printk("register_kprobe failed, returned %d\n", ret);
                printk("register_kprobe failed, returned %d\n", ret);

-               return -1;
+               return ret;

        }
        printk("kprobe registered\n");
        return 0;
 }
 
        }
        printk("kprobe registered\n");
        return 0;
 }
 

-void cleanup_module(void)
+static void __exit kprobe_exit(void)

 {
        unregister_kprobe(&kp);
        printk("kprobe unregistered\n");
 }
 
 {
        unregister_kprobe(&kp);
        printk("kprobe unregistered\n");
 }
 

+module_init(kprobe_init)
+module_exit(kprobe_exit)

 MODULE_LICENSE("GPL");
 ----- cut here -----
 
 MODULE_LICENSE("GPL");
 ----- cut here -----
 


@@ -459,7 +493,6 @@ the arguments of do_fork().
 #include <linux/fs.h>
 #include <linux/uio.h>
 #include <linux/kprobes.h>
 #include <linux/fs.h>
 #include <linux/uio.h>
 #include <linux/kprobes.h>

-#include <linux/kallsyms.h>

 
 /*
  * Jumper probe for do_fork.
 
 /*
  * Jumper probe for do_fork.


@@ -481,17 +514,13 @@ long jdo_fork(unsigned long clone_flags, unsigned long stack_start,
 }
 
 static struct jprobe my_jprobe = {
 }
 
 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;
 {
        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);
 
        if ((ret = register_jprobe(&my_jprobe)) <0) {
                printk("register_jprobe failed, returned %d\n", ret);


@@ -502,12 +531,14 @@ int init_module(void)
        return 0;
 }
 
        return 0;
 }
 

-void cleanup_module(void)
+static void __exit jprobe_exit(void)

 {
        unregister_jprobe(&my_jprobe);
        printk("jprobe unregistered\n");
 }
 
 {
        unregister_jprobe(&my_jprobe);
        printk("jprobe unregistered\n");
 }
 

+module_init(jprobe_init)
+module_exit(jprobe_exit)

 MODULE_LICENSE("GPL");
 ----- cut here -----
 
 MODULE_LICENSE("GPL");
 ----- cut here -----
 


@@ -526,16 +557,13 @@ report failed calls to sys_open().
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/kprobes.h>
 #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)
 {
 
 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);
        }
        if (retval < 0) {
                printk("%s returns %d\n", probed_func, retval);
        }


@@ -548,15 +576,11 @@ static struct kretprobe my_kretprobe = {
        .maxactive = 20
 };
 
        .maxactive = 20
 };
 

-int init_module(void)
+static int __init kretprobe_init(void)

 {
        int ret;
 {
        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;
        if ((ret = register_kretprobe(&my_kretprobe)) < 0) {
                printk("register_kretprobe failed, returned %d\n", ret);
                return -1;


@@ -565,7 +589,7 @@ int init_module(void)
        return 0;
 }
 
        return 0;
 }
 

-void cleanup_module(void)
+static void __exit kretprobe_exit(void)

 {
        unregister_kretprobe(&my_kretprobe);
        printk("kretprobe unregistered\n");
 {
        unregister_kretprobe(&my_kretprobe);
        printk("kretprobe unregistered\n");


@@ -574,6 +598,8 @@ void cleanup_module(void)
                my_kretprobe.nmissed, probed_func);
 }
 
                my_kretprobe.nmissed, probed_func);
 }
 

+module_init(kretprobe_init)
+module_exit(kretprobe_exit)

 MODULE_LICENSE("GPL");
 ----- cut here -----
 
 MODULE_LICENSE("GPL");
 ----- cut here -----
 


@@ -586,3 +612,5 @@ 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/
 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)