Title : Kernel Probes (Kprobes)
Authors : Jim Keniston <jkenisto@us.ibm.com>
- : Prasanna S Panchamukhi <prasanna@in.ibm.com>
+ : Prasanna S Panchamukhi <prasanna.panchamukhi@gmail.com>
+ : Masami Hiramatsu <mhiramat@redhat.com>
CONTENTS
8. Kprobes Example
9. Jprobes Example
10. Kretprobes Example
+Appendix A: The kprobes debugfs interface
+Appendix B: The kprobes sysctl interface
1. Concepts: Kprobes, Jprobes, Return Probes
the probe is to be inserted and what handler is to be called when
the probe is hit.
-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
-difference between a pre_handler and a post_handler, and how
-to use the maxactive and nmissed fields of a kretprobe. But
-if you're in a hurry to start using Kprobes, you can skip ahead
-to section 2.
+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 four subsections explain how the different types of
+probes work and how jump optimization works. They explain certain
+things that you'll need to know in order to make the best use of
+Kprobes -- e.g., the difference between a pre_handler and
+a post_handler, and how to use the maxactive and nmissed fields of
+a kretprobe. But if you're in a hurry to start using Kprobes, you
+can skip ahead to section 2.
1.1 How Does a Kprobe Work?
64 bytes on i386.
Note that the probed function's args may be passed on the stack
-or in registers (e.g., for x86_64 or for an i386 fastcall function).
-The jprobe will work in either case, so long as the handler's
-prototype matches that of the probed function.
+or in registers. The jprobe will work in either case, so long as the
+handler's prototype matches that of the probed function.
+
+1.3 Return Probes
-1.3 How Does a Return Probe Work?
+1.3.1 How Does a Return Probe Work?
When you call register_kretprobe(), Kprobes establishes a kprobe at
the entry to the function. When the probed function is called and this
When the probed function executes its return instruction, control
passes to the trampoline and that probe is hit. Kprobes' trampoline
-handler calls the user-specified handler associated with the kretprobe,
-then sets the saved instruction pointer to the saved return address,
-and that's where execution resumes upon return from the trap.
+handler calls the user-specified return handler associated with the
+kretprobe, then sets the saved instruction pointer to the saved return
+address, and that's where execution resumes upon return from the trap.
While the probed function is executing, its return address is
stored in an object of type kretprobe_instance. Before calling
time the probed function is entered but there is no kretprobe_instance
object available for establishing the return probe.
+1.3.2 Kretprobe entry-handler
+
+Kretprobes also provides an optional user-specified handler which runs
+on function entry. This handler is specified by setting the entry_handler
+field of the kretprobe struct. Whenever the kprobe placed by kretprobe at the
+function entry is hit, the user-defined entry_handler, if any, is invoked.
+If the entry_handler returns 0 (success) then a corresponding return handler
+is guaranteed to be called upon function return. If the entry_handler
+returns a non-zero error then Kprobes leaves the return address as is, and
+the kretprobe has no further effect for that particular function instance.
+
+Multiple entry and return handler invocations are matched using the unique
+kretprobe_instance object associated with them. Additionally, a user
+may also specify per return-instance private data to be part of each
+kretprobe_instance object. This is especially useful when sharing private
+data between corresponding user entry and return handlers. The size of each
+private data object can be specified at kretprobe registration time by
+setting the data_size field of the kretprobe struct. This data can be
+accessed through the data field of each kretprobe_instance object.
+
+In case probed function is entered but there is no kretprobe_instance
+object available, then in addition to incrementing the nmissed count,
+the user entry_handler invocation is also skipped.
+
+1.4 How Does Jump Optimization Work?
+
+If your kernel is built with CONFIG_OPTPROBES=y (currently this flag
+is automatically set 'y' on x86/x86-64, non-preemptive kernel) and
+the "debug.kprobes_optimization" kernel parameter is set to 1 (see
+sysctl(8)), Kprobes tries to reduce probe-hit overhead by using a jump
+instruction instead of a breakpoint instruction at each probepoint.
+
+1.4.1 Init a Kprobe
+
+When a probe is registered, before attempting this optimization,
+Kprobes inserts an ordinary, breakpoint-based kprobe at the specified
+address. So, even if it's not possible to optimize this particular
+probepoint, there'll be a probe there.
+
+1.4.2 Safety Check
+
+Before optimizing a probe, Kprobes performs the following safety checks:
+
+- Kprobes verifies that the region that will be replaced by the jump
+instruction (the "optimized region") lies entirely within one function.
+(A jump instruction is multiple bytes, and so may overlay multiple
+instructions.)
+
+- Kprobes analyzes the entire function and verifies that there is no
+jump into the optimized region. Specifically:
+ - the function contains no indirect jump;
+ - the function contains no instruction that causes an exception (since
+ the fixup code triggered by the exception could jump back into the
+ optimized region -- Kprobes checks the exception tables to verify this);
+ and
+ - there is no near jump to the optimized region (other than to the first
+ byte).
+
+- For each instruction in the optimized region, Kprobes verifies that
+the instruction can be executed out of line.
+
+1.4.3 Preparing Detour Buffer
+
+Next, Kprobes prepares a "detour" buffer, which contains the following
+instruction sequence:
+- code to push the CPU's registers (emulating a breakpoint trap)
+- a call to the trampoline code which calls user's probe handlers.
+- code to restore registers
+- the instructions from the optimized region
+- a jump back to the original execution path.
+
+1.4.4 Pre-optimization
+
+After preparing the detour buffer, Kprobes verifies that none of the
+following situations exist:
+- The probe has either a break_handler (i.e., it's a jprobe) or a
+post_handler.
+- Other instructions in the optimized region are probed.
+- The probe is disabled.
+In any of the above cases, Kprobes won't start optimizing the probe.
+Since these are temporary situations, Kprobes tries to start
+optimizing it again if the situation is changed.
+
+If the kprobe can be optimized, Kprobes enqueues the kprobe to an
+optimizing list, and kicks the kprobe-optimizer workqueue to optimize
+it. If the to-be-optimized probepoint is hit before being optimized,
+Kprobes returns control to the original instruction path by setting
+the CPU's instruction pointer to the copied code in the detour buffer
+-- thus at least avoiding the single-step.
+
+1.4.5 Optimization
+
+The Kprobe-optimizer doesn't insert the jump instruction immediately;
+rather, it calls synchronize_sched() for safety first, because it's
+possible for a CPU to be interrupted in the middle of executing the
+optimized region(*). As you know, synchronize_sched() can ensure
+that all interruptions that were active when synchronize_sched()
+was called are done, but only if CONFIG_PREEMPT=n. So, this version
+of kprobe optimization supports only kernels with CONFIG_PREEMPT=n.(**)
+
+After that, the Kprobe-optimizer calls stop_machine() to replace
+the optimized region with a jump instruction to the detour buffer,
+using text_poke_smp().
+
+1.4.6 Unoptimization
+
+When an optimized kprobe is unregistered, disabled, or blocked by
+another kprobe, it will be unoptimized. If this happens before
+the optimization is complete, the kprobe is just dequeued from the
+optimized list. If the optimization has been done, the jump is
+replaced with the original code (except for an int3 breakpoint in
+the first byte) by using text_poke_smp().
+
+(*)Please imagine that the 2nd instruction is interrupted and then
+the optimizer replaces the 2nd instruction with the jump *address*
+while the interrupt handler is running. When the interrupt
+returns to original address, there is no valid instruction,
+and it causes an unexpected result.
+
+(**)This optimization-safety checking may be replaced with the
+stop-machine method that ksplice uses for supporting a CONFIG_PREEMPT=y
+kernel.
+
+NOTE for geeks:
+The jump optimization changes the kprobe's pre_handler behavior.
+Without optimization, the pre_handler can change the kernel's execution
+path by changing regs->ip and returning 1. However, when the probe
+is optimized, that modification is ignored. Thus, if you want to
+tweak the kernel's execution path, you need to suppress optimization,
+using one of the following techniques:
+- Specify an empty function for the kprobe's post_handler or break_handler.
+ or
+- Execute 'sysctl -w debug.kprobes_optimization=n'
+
2. Architectures Supported
Kprobes, jprobes, and return probes are implemented on the following
architectures:
-- i386
-- x86_64 (AMD-64, EM64T)
+- i386 (Supports jump optimization)
+- x86_64 (AMD-64, EM64T) (Supports jump optimization)
- ppc64
- ia64 (Does not support probes on instruction slot1.)
- sparc64 (Return probes not yet implemented.)
+- arm
+- ppc
+- mips
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, its handlers aren't hit until calling enable_kprobe(kp).
NOTE:
1. With the introduction of the "symbol_name" field to struct kprobe,
The handler should have the same arg list and return type as the probed
function; and just before it returns, it must call jprobe_return().
(The handler never actually returns, since jprobe_return() returns
-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);
+control to Kprobes.) If the probed function is declared asmlinkage
+or anything else that affects how args are passed, the handler's
+declaration must match.
register_jprobe() returns 0 on success, or a negative errno otherwise.
- ret_addr: the return address
- rp: points to the corresponding kretprobe object
- task: points to the corresponding task struct
+- data: points to per return-instance private data; see "Kretprobe
+ entry-handler" for details.
The regs_return_value(regs) macro provides a simple abstraction to
extract the return value from the appropriate register as defined by
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,
however, there cannot be multiple jprobes on the same function at
-the same time.
+the same time. Also, a probepoint for which there is a jprobe or
+a post_handler cannot be optimized. So if you install a jprobe,
+or a kprobe with a post_handler, at an optimized probepoint, the
+probepoint will be unoptimized automatically.
In general, you can install a probe anywhere in the kernel.
In particular, you can probe interrupt handlers. Known exceptions
registration and unregistration.
Probe handlers are run with preemption disabled. Depending on the
-architecture, handlers may also run with interrupts disabled. In any
-case, your handler should not yield the CPU (e.g., by attempting to
-acquire a semaphore).
+architecture and optimization state, handlers may also run with
+interrupts disabled (e.g., kretprobe handlers and optimized kprobe
+handlers run without interrupt disabled on x86/x86-64). In any case,
+your handler should not yield the CPU (e.g., by attempting to acquire
+a semaphore).
Since a return probe is implemented by replacing the return
address with the trampoline's address, stack backtraces and calls
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.
+produce undesirable results. In such a case, a line:
+kretprobe BUG!: Processing kretprobe d000000000041aa8 @ c00000000004f48c
+gets printed. With this information, one will be able to correlate the
+exact instance of the kretprobe that caused the problem. 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
on the x86_64 version of __switch_to(); the registration functions
return -EINVAL.
+On x86/x86-64, since the Jump Optimization of Kprobes modifies
+instructions widely, there are some limitations to optimization. To
+explain it, we introduce some terminology. Imagine a 3-instruction
+sequence consisting of a two 2-byte instructions and one 3-byte
+instruction.
+
+ IA
+ |
+[-2][-1][0][1][2][3][4][5][6][7]
+ [ins1][ins2][ ins3 ]
+ [<- DCR ->]
+ [<- JTPR ->]
+
+ins1: 1st Instruction
+ins2: 2nd Instruction
+ins3: 3rd Instruction
+IA: Insertion Address
+JTPR: Jump Target Prohibition Region
+DCR: Detoured Code Region
+
+The instructions in DCR are copied to the out-of-line buffer
+of the kprobe, because the bytes in DCR are replaced by
+a 5-byte jump instruction. So there are several limitations.
+
+a) The instructions in DCR must be relocatable.
+b) The instructions in DCR must not include a call instruction.
+c) JTPR must not be targeted by any jump or call instruction.
+d) DCR must not straddle the border between functions.
+
+Anyway, these limitations are checked by the in-kernel instruction
+decoder, so you don't need to worry about that.
+
6. Probe Overhead
On a typical CPU in use in 2005, a kprobe hit takes 0.5 to 1.0
ppc64: POWER5 (gr), 1656 MHz (SMT disabled, 1 virtual CPU per physical CPU)
k = 0.77 usec; j = 1.31; r = 1.26; kr = 1.45; jr = 1.99
+6.1 Optimized Probe Overhead
+
+Typically, an optimized kprobe hit takes 0.07 to 0.1 microseconds to
+process. Here are sample overhead figures (in usec) for x86 architectures.
+k = unoptimized kprobe, b = boosted (single-step skipped), o = optimized kprobe,
+r = unoptimized kretprobe, rb = boosted kretprobe, ro = optimized kretprobe.
+
+i386: Intel(R) Xeon(R) E5410, 2.33GHz, 4656.90 bogomips
+k = 0.80 usec; b = 0.33; o = 0.05; r = 1.10; rb = 0.61; ro = 0.33
+
+x86-64: Intel(R) Xeon(R) E5410, 2.33GHz, 4656.90 bogomips
+k = 0.99 usec; b = 0.43; o = 0.06; r = 1.24; rb = 0.68; ro = 0.30
+
7. TODO
a. SystemTap (http://sourceware.org/systemtap): Provides a simplified
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";
-
- if ((ret = register_kprobe(&kp) < 0)) {
- printk("register_kprobe failed, returned %d\n", ret);
- return -1;
- }
- 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 = 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>
-
-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)
-{
- int retval = regs_return_value(regs);
- if (retval < 0) {
- printk("%s returns %d\n", probed_func, retval);
- }
- return 0;
-}
-
-static struct kretprobe my_kretprobe = {
- .handler = ret_handler,
- /* Probe up to 20 instances concurrently. */
- .maxactive = 20
-};
-
-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("Planted return probe at %p\n", my_kretprobe.kp.addr);
- 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
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)
+
+
+Appendix A: The kprobes debugfs interface
+
+With recent kernels (> 2.6.20) the list of registered kprobes is visible
+under the /sys/kernel/debug/kprobes/ directory (assuming debugfs is mounted at //sys/kernel/debug).
+
+/sys/kernel/debug/kprobes/list: Lists all registered probes on the system
+
+c015d71a k vfs_read+0x0
+c011a316 j do_fork+0x0
+c03dedc5 r tcp_v4_rcv+0x0
+
+The first column provides the kernel address where the probe is inserted.
+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. 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]. If the probe is optimized, it is
+marked with [OPTIMIZED].
+
+/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.
+
+
+Appendix B: The kprobes sysctl interface
+
+/proc/sys/debug/kprobes-optimization: Turn kprobes optimization ON/OFF.
+
+When CONFIG_OPTPROBES=y, this sysctl interface appears and it provides
+a knob to globally and forcibly turn jump optimization (see section
+1.4) ON or OFF. By default, jump optimization is allowed (ON).
+If you echo "0" to this file or set "debug.kprobes_optimization" to
+0 via sysctl, all optimized probes will be unoptimized, and any new
+probes registered after that will not be optimized. Note that this
+knob *changes* the optimized state. This means that optimized probes
+(marked [OPTIMIZED]) will be unoptimized ([OPTIMIZED] tag will be
+removed). If the knob is turned on, they will be optimized again.
+
Code Review / linux-2.6.git / blobdiff