Root/
1 | Title : Kernel Probes (Kprobes) |
2 | Authors : Jim Keniston <jkenisto@us.ibm.com> |
3 | : Prasanna S Panchamukhi <prasanna@in.ibm.com> |
4 | |
5 | CONTENTS |
6 | |
7 | 1. Concepts: Kprobes, Jprobes, Return Probes |
8 | 2. Architectures Supported |
9 | 3. Configuring Kprobes |
10 | 4. API Reference |
11 | 5. Kprobes Features and Limitations |
12 | 6. Probe Overhead |
13 | 7. TODO |
14 | 8. Kprobes Example |
15 | 9. Jprobes Example |
16 | 10. Kretprobes Example |
17 | Appendix A: The kprobes debugfs interface |
18 | |
19 | 1. Concepts: Kprobes, Jprobes, Return Probes |
20 | |
21 | Kprobes enables you to dynamically break into any kernel routine and |
22 | collect debugging and performance information non-disruptively. You |
23 | can trap at almost any kernel code address, specifying a handler |
24 | routine to be invoked when the breakpoint is hit. |
25 | |
26 | There are currently three types of probes: kprobes, jprobes, and |
27 | kretprobes (also called return probes). A kprobe can be inserted |
28 | on virtually any instruction in the kernel. A jprobe is inserted at |
29 | the entry to a kernel function, and provides convenient access to the |
30 | function's arguments. A return probe fires when a specified function |
31 | returns. |
32 | |
33 | In the typical case, Kprobes-based instrumentation is packaged as |
34 | a kernel module. The module's init function installs ("registers") |
35 | one or more probes, and the exit function unregisters them. A |
36 | registration function such as register_kprobe() specifies where |
37 | the probe is to be inserted and what handler is to be called when |
38 | the probe is hit. |
39 | |
40 | There are also register_/unregister_*probes() functions for batch |
41 | registration/unregistration of a group of *probes. These functions |
42 | can speed up unregistration process when you have to unregister |
43 | a lot of probes at once. |
44 | |
45 | The next three subsections explain how the different types of |
46 | probes work. They explain certain things that you'll need to |
47 | know in order to make the best use of Kprobes -- e.g., the |
48 | difference between a pre_handler and a post_handler, and how |
49 | to use the maxactive and nmissed fields of a kretprobe. But |
50 | if you're in a hurry to start using Kprobes, you can skip ahead |
51 | to section 2. |
52 | |
53 | 1.1 How Does a Kprobe Work? |
54 | |
55 | When a kprobe is registered, Kprobes makes a copy of the probed |
56 | instruction and replaces the first byte(s) of the probed instruction |
57 | with a breakpoint instruction (e.g., int3 on i386 and x86_64). |
58 | |
59 | When a CPU hits the breakpoint instruction, a trap occurs, the CPU's |
60 | registers are saved, and control passes to Kprobes via the |
61 | notifier_call_chain mechanism. Kprobes executes the "pre_handler" |
62 | associated with the kprobe, passing the handler the addresses of the |
63 | kprobe struct and the saved registers. |
64 | |
65 | Next, Kprobes single-steps its copy of the probed instruction. |
66 | (It would be simpler to single-step the actual instruction in place, |
67 | but then Kprobes would have to temporarily remove the breakpoint |
68 | instruction. This would open a small time window when another CPU |
69 | could sail right past the probepoint.) |
70 | |
71 | After the instruction is single-stepped, Kprobes executes the |
72 | "post_handler," if any, that is associated with the kprobe. |
73 | Execution then continues with the instruction following the probepoint. |
74 | |
75 | 1.2 How Does a Jprobe Work? |
76 | |
77 | A jprobe is implemented using a kprobe that is placed on a function's |
78 | entry point. It employs a simple mirroring principle to allow |
79 | seamless access to the probed function's arguments. The jprobe |
80 | handler routine should have the same signature (arg list and return |
81 | type) as the function being probed, and must always end by calling |
82 | the Kprobes function jprobe_return(). |
83 | |
84 | Here's how it works. When the probe is hit, Kprobes makes a copy of |
85 | the saved registers and a generous portion of the stack (see below). |
86 | Kprobes then points the saved instruction pointer at the jprobe's |
87 | handler routine, and returns from the trap. As a result, control |
88 | passes to the handler, which is presented with the same register and |
89 | stack contents as the probed function. When it is done, the handler |
90 | calls jprobe_return(), which traps again to restore the original stack |
91 | contents and processor state and switch to the probed function. |
92 | |
93 | By convention, the callee owns its arguments, so gcc may produce code |
94 | that unexpectedly modifies that portion of the stack. This is why |
95 | Kprobes saves a copy of the stack and restores it after the jprobe |
96 | handler has run. Up to MAX_STACK_SIZE bytes are copied -- e.g., |
97 | 64 bytes on i386. |
98 | |
99 | Note that the probed function's args may be passed on the stack |
100 | or in registers. The jprobe will work in either case, so long as the |
101 | handler's prototype matches that of the probed function. |
102 | |
103 | 1.3 Return Probes |
104 | |
105 | 1.3.1 How Does a Return Probe Work? |
106 | |
107 | When you call register_kretprobe(), Kprobes establishes a kprobe at |
108 | the entry to the function. When the probed function is called and this |
109 | probe is hit, Kprobes saves a copy of the return address, and replaces |
110 | the return address with the address of a "trampoline." The trampoline |
111 | is an arbitrary piece of code -- typically just a nop instruction. |
112 | At boot time, Kprobes registers a kprobe at the trampoline. |
113 | |
114 | When the probed function executes its return instruction, control |
115 | passes to the trampoline and that probe is hit. Kprobes' trampoline |
116 | handler calls the user-specified return handler associated with the |
117 | kretprobe, then sets the saved instruction pointer to the saved return |
118 | address, and that's where execution resumes upon return from the trap. |
119 | |
120 | While the probed function is executing, its return address is |
121 | stored in an object of type kretprobe_instance. Before calling |
122 | register_kretprobe(), the user sets the maxactive field of the |
123 | kretprobe struct to specify how many instances of the specified |
124 | function can be probed simultaneously. register_kretprobe() |
125 | pre-allocates the indicated number of kretprobe_instance objects. |
126 | |
127 | For example, if the function is non-recursive and is called with a |
128 | spinlock held, maxactive = 1 should be enough. If the function is |
129 | non-recursive and can never relinquish the CPU (e.g., via a semaphore |
130 | or preemption), NR_CPUS should be enough. If maxactive <= 0, it is |
131 | set to a default value. If CONFIG_PREEMPT is enabled, the default |
132 | is max(10, 2*NR_CPUS). Otherwise, the default is NR_CPUS. |
133 | |
134 | It's not a disaster if you set maxactive too low; you'll just miss |
135 | some probes. In the kretprobe struct, the nmissed field is set to |
136 | zero when the return probe is registered, and is incremented every |
137 | time the probed function is entered but there is no kretprobe_instance |
138 | object available for establishing the return probe. |
139 | |
140 | 1.3.2 Kretprobe entry-handler |
141 | |
142 | Kretprobes also provides an optional user-specified handler which runs |
143 | on function entry. This handler is specified by setting the entry_handler |
144 | field of the kretprobe struct. Whenever the kprobe placed by kretprobe at the |
145 | function entry is hit, the user-defined entry_handler, if any, is invoked. |
146 | If the entry_handler returns 0 (success) then a corresponding return handler |
147 | is guaranteed to be called upon function return. If the entry_handler |
148 | returns a non-zero error then Kprobes leaves the return address as is, and |
149 | the kretprobe has no further effect for that particular function instance. |
150 | |
151 | Multiple entry and return handler invocations are matched using the unique |
152 | kretprobe_instance object associated with them. Additionally, a user |
153 | may also specify per return-instance private data to be part of each |
154 | kretprobe_instance object. This is especially useful when sharing private |
155 | data between corresponding user entry and return handlers. The size of each |
156 | private data object can be specified at kretprobe registration time by |
157 | setting the data_size field of the kretprobe struct. This data can be |
158 | accessed through the data field of each kretprobe_instance object. |
159 | |
160 | In case probed function is entered but there is no kretprobe_instance |
161 | object available, then in addition to incrementing the nmissed count, |
162 | the user entry_handler invocation is also skipped. |
163 | |
164 | 2. Architectures Supported |
165 | |
166 | Kprobes, jprobes, and return probes are implemented on the following |
167 | architectures: |
168 | |
169 | - i386 |
170 | - x86_64 (AMD-64, EM64T) |
171 | - ppc64 |
172 | - ia64 (Does not support probes on instruction slot1.) |
173 | - sparc64 (Return probes not yet implemented.) |
174 | - arm |
175 | - ppc |
176 | |
177 | 3. Configuring Kprobes |
178 | |
179 | When configuring the kernel using make menuconfig/xconfig/oldconfig, |
180 | ensure that CONFIG_KPROBES is set to "y". Under "Instrumentation |
181 | Support", look for "Kprobes". |
182 | |
183 | So that you can load and unload Kprobes-based instrumentation modules, |
184 | make sure "Loadable module support" (CONFIG_MODULES) and "Module |
185 | unloading" (CONFIG_MODULE_UNLOAD) are set to "y". |
186 | |
187 | Also make sure that CONFIG_KALLSYMS and perhaps even CONFIG_KALLSYMS_ALL |
188 | are set to "y", since kallsyms_lookup_name() is used by the in-kernel |
189 | kprobe address resolution code. |
190 | |
191 | If you need to insert a probe in the middle of a function, you may find |
192 | it useful to "Compile the kernel with debug info" (CONFIG_DEBUG_INFO), |
193 | so you can use "objdump -d -l vmlinux" to see the source-to-object |
194 | code mapping. |
195 | |
196 | 4. API Reference |
197 | |
198 | The Kprobes API includes a "register" function and an "unregister" |
199 | function for each type of probe. The API also includes "register_*probes" |
200 | and "unregister_*probes" functions for (un)registering arrays of probes. |
201 | Here are terse, mini-man-page specifications for these functions and |
202 | the associated probe handlers that you'll write. See the files in the |
203 | samples/kprobes/ sub-directory for examples. |
204 | |
205 | 4.1 register_kprobe |
206 | |
207 | #include <linux/kprobes.h> |
208 | int register_kprobe(struct kprobe *kp); |
209 | |
210 | Sets a breakpoint at the address kp->addr. When the breakpoint is |
211 | hit, Kprobes calls kp->pre_handler. After the probed instruction |
212 | is single-stepped, Kprobe calls kp->post_handler. If a fault |
213 | occurs during execution of kp->pre_handler or kp->post_handler, |
214 | or during single-stepping of the probed instruction, Kprobes calls |
215 | kp->fault_handler. Any or all handlers can be NULL. If kp->flags |
216 | is set KPROBE_FLAG_DISABLED, that kp will be registered but disabled, |
217 | so, it's handlers aren't hit until calling enable_kprobe(kp). |
218 | |
219 | NOTE: |
220 | 1. With the introduction of the "symbol_name" field to struct kprobe, |
221 | the probepoint address resolution will now be taken care of by the kernel. |
222 | The following will now work: |
223 | |
224 | kp.symbol_name = "symbol_name"; |
225 | |
226 | (64-bit powerpc intricacies such as function descriptors are handled |
227 | transparently) |
228 | |
229 | 2. Use the "offset" field of struct kprobe if the offset into the symbol |
230 | to install a probepoint is known. This field is used to calculate the |
231 | probepoint. |
232 | |
233 | 3. Specify either the kprobe "symbol_name" OR the "addr". If both are |
234 | specified, kprobe registration will fail with -EINVAL. |
235 | |
236 | 4. With CISC architectures (such as i386 and x86_64), the kprobes code |
237 | does not validate if the kprobe.addr is at an instruction boundary. |
238 | Use "offset" with caution. |
239 | |
240 | register_kprobe() returns 0 on success, or a negative errno otherwise. |
241 | |
242 | User's pre-handler (kp->pre_handler): |
243 | #include <linux/kprobes.h> |
244 | #include <linux/ptrace.h> |
245 | int pre_handler(struct kprobe *p, struct pt_regs *regs); |
246 | |
247 | Called with p pointing to the kprobe associated with the breakpoint, |
248 | and regs pointing to the struct containing the registers saved when |
249 | the breakpoint was hit. Return 0 here unless you're a Kprobes geek. |
250 | |
251 | User's post-handler (kp->post_handler): |
252 | #include <linux/kprobes.h> |
253 | #include <linux/ptrace.h> |
254 | void post_handler(struct kprobe *p, struct pt_regs *regs, |
255 | unsigned long flags); |
256 | |
257 | p and regs are as described for the pre_handler. flags always seems |
258 | to be zero. |
259 | |
260 | User's fault-handler (kp->fault_handler): |
261 | #include <linux/kprobes.h> |
262 | #include <linux/ptrace.h> |
263 | int fault_handler(struct kprobe *p, struct pt_regs *regs, int trapnr); |
264 | |
265 | p and regs are as described for the pre_handler. trapnr is the |
266 | architecture-specific trap number associated with the fault (e.g., |
267 | on i386, 13 for a general protection fault or 14 for a page fault). |
268 | Returns 1 if it successfully handled the exception. |
269 | |
270 | 4.2 register_jprobe |
271 | |
272 | #include <linux/kprobes.h> |
273 | int register_jprobe(struct jprobe *jp) |
274 | |
275 | Sets a breakpoint at the address jp->kp.addr, which must be the address |
276 | of the first instruction of a function. When the breakpoint is hit, |
277 | Kprobes runs the handler whose address is jp->entry. |
278 | |
279 | The handler should have the same arg list and return type as the probed |
280 | function; and just before it returns, it must call jprobe_return(). |
281 | (The handler never actually returns, since jprobe_return() returns |
282 | control to Kprobes.) If the probed function is declared asmlinkage |
283 | or anything else that affects how args are passed, the handler's |
284 | declaration must match. |
285 | |
286 | register_jprobe() returns 0 on success, or a negative errno otherwise. |
287 | |
288 | 4.3 register_kretprobe |
289 | |
290 | #include <linux/kprobes.h> |
291 | int register_kretprobe(struct kretprobe *rp); |
292 | |
293 | Establishes a return probe for the function whose address is |
294 | rp->kp.addr. When that function returns, Kprobes calls rp->handler. |
295 | You must set rp->maxactive appropriately before you call |
296 | register_kretprobe(); see "How Does a Return Probe Work?" for details. |
297 | |
298 | register_kretprobe() returns 0 on success, or a negative errno |
299 | otherwise. |
300 | |
301 | User's return-probe handler (rp->handler): |
302 | #include <linux/kprobes.h> |
303 | #include <linux/ptrace.h> |
304 | int kretprobe_handler(struct kretprobe_instance *ri, struct pt_regs *regs); |
305 | |
306 | regs is as described for kprobe.pre_handler. ri points to the |
307 | kretprobe_instance object, of which the following fields may be |
308 | of interest: |
309 | - ret_addr: the return address |
310 | - rp: points to the corresponding kretprobe object |
311 | - task: points to the corresponding task struct |
312 | - data: points to per return-instance private data; see "Kretprobe |
313 | entry-handler" for details. |
314 | |
315 | The regs_return_value(regs) macro provides a simple abstraction to |
316 | extract the return value from the appropriate register as defined by |
317 | the architecture's ABI. |
318 | |
319 | The handler's return value is currently ignored. |
320 | |
321 | 4.4 unregister_*probe |
322 | |
323 | #include <linux/kprobes.h> |
324 | void unregister_kprobe(struct kprobe *kp); |
325 | void unregister_jprobe(struct jprobe *jp); |
326 | void unregister_kretprobe(struct kretprobe *rp); |
327 | |
328 | Removes the specified probe. The unregister function can be called |
329 | at any time after the probe has been registered. |
330 | |
331 | NOTE: |
332 | If the functions find an incorrect probe (ex. an unregistered probe), |
333 | they clear the addr field of the probe. |
334 | |
335 | 4.5 register_*probes |
336 | |
337 | #include <linux/kprobes.h> |
338 | int register_kprobes(struct kprobe **kps, int num); |
339 | int register_kretprobes(struct kretprobe **rps, int num); |
340 | int register_jprobes(struct jprobe **jps, int num); |
341 | |
342 | Registers each of the num probes in the specified array. If any |
343 | error occurs during registration, all probes in the array, up to |
344 | the bad probe, are safely unregistered before the register_*probes |
345 | function returns. |
346 | - kps/rps/jps: an array of pointers to *probe data structures |
347 | - num: the number of the array entries. |
348 | |
349 | NOTE: |
350 | You have to allocate(or define) an array of pointers and set all |
351 | of the array entries before using these functions. |
352 | |
353 | 4.6 unregister_*probes |
354 | |
355 | #include <linux/kprobes.h> |
356 | void unregister_kprobes(struct kprobe **kps, int num); |
357 | void unregister_kretprobes(struct kretprobe **rps, int num); |
358 | void unregister_jprobes(struct jprobe **jps, int num); |
359 | |
360 | Removes each of the num probes in the specified array at once. |
361 | |
362 | NOTE: |
363 | If the functions find some incorrect probes (ex. unregistered |
364 | probes) in the specified array, they clear the addr field of those |
365 | incorrect probes. However, other probes in the array are |
366 | unregistered correctly. |
367 | |
368 | 4.7 disable_*probe |
369 | |
370 | #include <linux/kprobes.h> |
371 | int disable_kprobe(struct kprobe *kp); |
372 | int disable_kretprobe(struct kretprobe *rp); |
373 | int disable_jprobe(struct jprobe *jp); |
374 | |
375 | Temporarily disables the specified *probe. You can enable it again by using |
376 | enable_*probe(). You must specify the probe which has been registered. |
377 | |
378 | 4.8 enable_*probe |
379 | |
380 | #include <linux/kprobes.h> |
381 | int enable_kprobe(struct kprobe *kp); |
382 | int enable_kretprobe(struct kretprobe *rp); |
383 | int enable_jprobe(struct jprobe *jp); |
384 | |
385 | Enables *probe which has been disabled by disable_*probe(). You must specify |
386 | the probe which has been registered. |
387 | |
388 | 5. Kprobes Features and Limitations |
389 | |
390 | Kprobes allows multiple probes at the same address. Currently, |
391 | however, there cannot be multiple jprobes on the same function at |
392 | the same time. |
393 | |
394 | In general, you can install a probe anywhere in the kernel. |
395 | In particular, you can probe interrupt handlers. Known exceptions |
396 | are discussed in this section. |
397 | |
398 | The register_*probe functions will return -EINVAL if you attempt |
399 | to install a probe in the code that implements Kprobes (mostly |
400 | kernel/kprobes.c and arch/*/kernel/kprobes.c, but also functions such |
401 | as do_page_fault and notifier_call_chain). |
402 | |
403 | If you install a probe in an inline-able function, Kprobes makes |
404 | no attempt to chase down all inline instances of the function and |
405 | install probes there. gcc may inline a function without being asked, |
406 | so keep this in mind if you're not seeing the probe hits you expect. |
407 | |
408 | A probe handler can modify the environment of the probed function |
409 | -- e.g., by modifying kernel data structures, or by modifying the |
410 | contents of the pt_regs struct (which are restored to the registers |
411 | upon return from the breakpoint). So Kprobes can be used, for example, |
412 | to install a bug fix or to inject faults for testing. Kprobes, of |
413 | course, has no way to distinguish the deliberately injected faults |
414 | from the accidental ones. Don't drink and probe. |
415 | |
416 | Kprobes makes no attempt to prevent probe handlers from stepping on |
417 | each other -- e.g., probing printk() and then calling printk() from a |
418 | probe handler. If a probe handler hits a probe, that second probe's |
419 | handlers won't be run in that instance, and the kprobe.nmissed member |
420 | of the second probe will be incremented. |
421 | |
422 | As of Linux v2.6.15-rc1, multiple handlers (or multiple instances of |
423 | the same handler) may run concurrently on different CPUs. |
424 | |
425 | Kprobes does not use mutexes or allocate memory except during |
426 | registration and unregistration. |
427 | |
428 | Probe handlers are run with preemption disabled. Depending on the |
429 | architecture, handlers may also run with interrupts disabled. In any |
430 | case, your handler should not yield the CPU (e.g., by attempting to |
431 | acquire a semaphore). |
432 | |
433 | Since a return probe is implemented by replacing the return |
434 | address with the trampoline's address, stack backtraces and calls |
435 | to __builtin_return_address() will typically yield the trampoline's |
436 | address instead of the real return address for kretprobed functions. |
437 | (As far as we can tell, __builtin_return_address() is used only |
438 | for instrumentation and error reporting.) |
439 | |
440 | If the number of times a function is called does not match the number |
441 | of times it returns, registering a return probe on that function may |
442 | produce undesirable results. In such a case, a line: |
443 | kretprobe BUG!: Processing kretprobe d000000000041aa8 @ c00000000004f48c |
444 | gets printed. With this information, one will be able to correlate the |
445 | exact instance of the kretprobe that caused the problem. We have the |
446 | do_exit() case covered. do_execve() and do_fork() are not an issue. |
447 | We're unaware of other specific cases where this could be a problem. |
448 | |
449 | If, upon entry to or exit from a function, the CPU is running on |
450 | a stack other than that of the current task, registering a return |
451 | probe on that function may produce undesirable results. For this |
452 | reason, Kprobes doesn't support return probes (or kprobes or jprobes) |
453 | on the x86_64 version of __switch_to(); the registration functions |
454 | return -EINVAL. |
455 | |
456 | 6. Probe Overhead |
457 | |
458 | On a typical CPU in use in 2005, a kprobe hit takes 0.5 to 1.0 |
459 | microseconds to process. Specifically, a benchmark that hits the same |
460 | probepoint repeatedly, firing a simple handler each time, reports 1-2 |
461 | million hits per second, depending on the architecture. A jprobe or |
462 | return-probe hit typically takes 50-75% longer than a kprobe hit. |
463 | When you have a return probe set on a function, adding a kprobe at |
464 | the entry to that function adds essentially no overhead. |
465 | |
466 | Here are sample overhead figures (in usec) for different architectures. |
467 | k = kprobe; j = jprobe; r = return probe; kr = kprobe + return probe |
468 | on same function; jr = jprobe + return probe on same function |
469 | |
470 | i386: Intel Pentium M, 1495 MHz, 2957.31 bogomips |
471 | k = 0.57 usec; j = 1.00; r = 0.92; kr = 0.99; jr = 1.40 |
472 | |
473 | x86_64: AMD Opteron 246, 1994 MHz, 3971.48 bogomips |
474 | k = 0.49 usec; j = 0.76; r = 0.80; kr = 0.82; jr = 1.07 |
475 | |
476 | ppc64: POWER5 (gr), 1656 MHz (SMT disabled, 1 virtual CPU per physical CPU) |
477 | k = 0.77 usec; j = 1.31; r = 1.26; kr = 1.45; jr = 1.99 |
478 | |
479 | 7. TODO |
480 | |
481 | a. SystemTap (http://sourceware.org/systemtap): Provides a simplified |
482 | programming interface for probe-based instrumentation. Try it out. |
483 | b. Kernel return probes for sparc64. |
484 | c. Support for other architectures. |
485 | d. User-space probes. |
486 | e. Watchpoint probes (which fire on data references). |
487 | |
488 | 8. Kprobes Example |
489 | |
490 | See samples/kprobes/kprobe_example.c |
491 | |
492 | 9. Jprobes Example |
493 | |
494 | See samples/kprobes/jprobe_example.c |
495 | |
496 | 10. Kretprobes Example |
497 | |
498 | See samples/kprobes/kretprobe_example.c |
499 | |
500 | For additional information on Kprobes, refer to the following URLs: |
501 | http://www-106.ibm.com/developerworks/library/l-kprobes.html?ca=dgr-lnxw42Kprobe |
502 | http://www.redhat.com/magazine/005mar05/features/kprobes/ |
503 | http://www-users.cs.umn.edu/~boutcher/kprobes/ |
504 | http://www.linuxsymposium.org/2006/linuxsymposium_procv2.pdf (pages 101-115) |
505 | |
506 | |
507 | Appendix A: The kprobes debugfs interface |
508 | |
509 | With recent kernels (> 2.6.20) the list of registered kprobes is visible |
510 | under the /sys/kernel/debug/kprobes/ directory (assuming debugfs is mounted at //sys/kernel/debug). |
511 | |
512 | /sys/kernel/debug/kprobes/list: Lists all registered probes on the system |
513 | |
514 | c015d71a k vfs_read+0x0 |
515 | c011a316 j do_fork+0x0 |
516 | c03dedc5 r tcp_v4_rcv+0x0 |
517 | |
518 | The first column provides the kernel address where the probe is inserted. |
519 | The second column identifies the type of probe (k - kprobe, r - kretprobe |
520 | and j - jprobe), while the third column specifies the symbol+offset of |
521 | the probe. If the probed function belongs to a module, the module name |
522 | is also specified. Following columns show probe status. If the probe is on |
523 | a virtual address that is no longer valid (module init sections, module |
524 | virtual addresses that correspond to modules that've been unloaded), |
525 | such probes are marked with [GONE]. If the probe is temporarily disabled, |
526 | such probes are marked with [DISABLED]. |
527 | |
528 | /sys/kernel/debug/kprobes/enabled: Turn kprobes ON/OFF forcibly. |
529 | |
530 | Provides a knob to globally and forcibly turn registered kprobes ON or OFF. |
531 | By default, all kprobes are enabled. By echoing "0" to this file, all |
532 | registered probes will be disarmed, till such time a "1" is echoed to this |
533 | file. Note that this knob just disarms and arms all kprobes and doesn't |
534 | change each probe's disabling state. This means that disabled kprobes (marked |
535 | [DISABLED]) will be not enabled if you turn ON all kprobes by this knob. |
536 |
Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master
Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9