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kprobes.txt: standardize document format 

Each text file under Documentation follows a different
format. Some doesn't even have titles!

Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx:

- comment the contents;
- add proper markups for titles;
- mark literal blocks as such;
- use :Author: for authorship;
- use the right markups for footnotes;
- escape some literals that would otherwise cause problems;
- fix identation and add blank lines where needed.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mauro Carvalho Chehab 2017-05-14 16:51:34 -03:00 committed by Jonathan Corbet
parent 7472723305
commit a1dac76762
1 changed files with 276 additions and 192 deletions
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468
Documentation/kprobes.txt
View File

@ -1,30 +1,36 @@
Title : Kernel Probes (Kprobes) =======================
Authors : Jim Keniston <jkenisto@us.ibm.com> Kernel Probes (Kprobes)
: Prasanna S Panchamukhi <prasanna.panchamukhi@gmail.com> =======================
: Masami Hiramatsu <mhiramat@redhat.com>
CONTENTS :Author: Jim Keniston <jkenisto@us.ibm.com>
:Author: Prasanna S Panchamukhi <prasanna.panchamukhi@gmail.com>
:Author: Masami Hiramatsu <mhiramat@redhat.com>
1. Concepts: Kprobes, Jprobes, Return Probes .. CONTENTS
2. Architectures Supported
3. Configuring Kprobes
4. API Reference
5. Kprobes Features and Limitations
6. Probe Overhead
7. TODO
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 1. Concepts: Kprobes, Jprobes, Return Probes
2. Architectures Supported
3. Configuring Kprobes
4. API Reference
5. Kprobes Features and Limitations
6. Probe Overhead
7. TODO
8. Kprobes Example
9. Jprobes Example
10. Kretprobes Example
Appendix A: The kprobes debugfs interface
Appendix B: The kprobes sysctl interface
Concepts: Kprobes, Jprobes, Return Probes
=========================================
Kprobes enables you to dynamically break into any kernel routine and Kprobes enables you to dynamically break into any kernel routine and
collect debugging and performance information non-disruptively. You collect debugging and performance information non-disruptively. You
can trap at almost any kernel code address(*), specifying a handler can trap at almost any kernel code address [1]_, specifying a handler
routine to be invoked when the breakpoint is hit. routine to be invoked when the breakpoint is hit.
(*: some parts of the kernel code can not be trapped, see 1.5 Blacklist)
.. [1] some parts of the kernel code can not be trapped, see
:ref:`kprobes_blacklist`)
There are currently three types of probes: kprobes, jprobes, and There are currently three types of probes: kprobes, jprobes, and
kretprobes (also called return probes). A kprobe can be inserted kretprobes (also called return probes). A kprobe can be inserted
@ -40,8 +46,8 @@ registration function such as register_kprobe() specifies where
the probe is to be inserted and what handler is to be called when the probe is to be inserted and what handler is to be called when
the probe is hit. the probe is hit.
There are also register_/unregister_*probes() functions for batch There are also ``register_/unregister_*probes()`` functions for batch
registration/unregistration of a group of *probes. These functions registration/unregistration of a group of ``*probes``. These functions
can speed up unregistration process when you have to unregister can speed up unregistration process when you have to unregister
a lot of probes at once. a lot of probes at once.
@ -51,9 +57,10 @@ 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 Kprobes -- e.g., the difference between a pre_handler and
a post_handler, and how to use the maxactive and nmissed fields of 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 a kretprobe. But if you're in a hurry to start using Kprobes, you
can skip ahead to section 2. can skip ahead to :ref:`kprobes_archs_supported`.
1.1 How Does a Kprobe Work? How Does a Kprobe Work?
-----------------------
When a kprobe is registered, Kprobes makes a copy of the probed When a kprobe is registered, Kprobes makes a copy of the probed
instruction and replaces the first byte(s) of the probed instruction instruction and replaces the first byte(s) of the probed instruction
@ -75,7 +82,8 @@ After the instruction is single-stepped, Kprobes executes the
"post_handler," if any, that is associated with the kprobe. "post_handler," if any, that is associated with the kprobe.
Execution then continues with the instruction following the probepoint. Execution then continues with the instruction following the probepoint.
1.2 How Does a Jprobe Work? How Does a Jprobe Work?
-----------------------
A jprobe is implemented using a kprobe that is placed on a function's A jprobe is implemented using a kprobe that is placed on a function's
entry point. It employs a simple mirroring principle to allow entry point. It employs a simple mirroring principle to allow
@ -113,9 +121,11 @@ more than eight function arguments, an argument of more than sixteen
bytes, or more than 64 bytes of argument data, depending on bytes, or more than 64 bytes of argument data, depending on
architecture). architecture).
1.3 Return Probes Return Probes
-------------
1.3.1 How Does a Return Probe Work? How Does a Return Probe Work?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
When you call register_kretprobe(), Kprobes establishes a kprobe at When you call register_kretprobe(), Kprobes establishes a kprobe at
the entry to the function. When the probed function is called and this the entry to the function. When the probed function is called and this
@ -150,7 +160,8 @@ zero when the return probe is registered, and is incremented every
time the probed function is entered but there is no kretprobe_instance time the probed function is entered but there is no kretprobe_instance
object available for establishing the return probe. object available for establishing the return probe.
1.3.2 Kretprobe entry-handler Kretprobe entry-handler
^^^^^^^^^^^^^^^^^^^^^^^
Kretprobes also provides an optional user-specified handler which runs Kretprobes also provides an optional user-specified handler which runs
on function entry. This handler is specified by setting the entry_handler on function entry. This handler is specified by setting the entry_handler
@ -174,7 +185,10 @@ In case probed function is entered but there is no kretprobe_instance
object available, then in addition to incrementing the nmissed count, object available, then in addition to incrementing the nmissed count,
the user entry_handler invocation is also skipped. the user entry_handler invocation is also skipped.
1.4 How Does Jump Optimization Work? .. _kprobes_jump_optimization:
How Does Jump Optimization Work?
--------------------------------
If your kernel is built with CONFIG_OPTPROBES=y (currently this flag If your kernel is built with CONFIG_OPTPROBES=y (currently this flag
is automatically set 'y' on x86/x86-64, non-preemptive kernel) and is automatically set 'y' on x86/x86-64, non-preemptive kernel) and
@ -182,53 +196,60 @@ the "debug.kprobes_optimization" kernel parameter is set to 1 (see
sysctl(8)), Kprobes tries to reduce probe-hit overhead by using a jump sysctl(8)), Kprobes tries to reduce probe-hit overhead by using a jump
instruction instead of a breakpoint instruction at each probepoint. instruction instead of a breakpoint instruction at each probepoint.
1.4.1 Init a Kprobe Init a Kprobe
^^^^^^^^^^^^^
When a probe is registered, before attempting this optimization, When a probe is registered, before attempting this optimization,
Kprobes inserts an ordinary, breakpoint-based kprobe at the specified Kprobes inserts an ordinary, breakpoint-based kprobe at the specified
address. So, even if it's not possible to optimize this particular address. So, even if it's not possible to optimize this particular
probepoint, there'll be a probe there. probepoint, there'll be a probe there.
1.4.2 Safety Check Safety Check
^^^^^^^^^^^^
Before optimizing a probe, Kprobes performs the following safety checks: Before optimizing a probe, Kprobes performs the following safety checks:
- Kprobes verifies that the region that will be replaced by the jump - Kprobes verifies that the region that will be replaced by the jump
instruction (the "optimized region") lies entirely within one function. instruction (the "optimized region") lies entirely within one function.
(A jump instruction is multiple bytes, and so may overlay multiple (A jump instruction is multiple bytes, and so may overlay multiple
instructions.) instructions.)
- Kprobes analyzes the entire function and verifies that there is no - Kprobes analyzes the entire function and verifies that there is no
jump into the optimized region. Specifically: jump into the optimized region. Specifically:
- the function contains no indirect jump; - the function contains no indirect jump;
- the function contains no instruction that causes an exception (since - the function contains no instruction that causes an exception (since
the fixup code triggered by the exception could jump back into the the fixup code triggered by the exception could jump back into the
optimized region -- Kprobes checks the exception tables to verify this); 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 - there is no near jump to the optimized region (other than to the first
byte). byte).
- For each instruction in the optimized region, Kprobes verifies that - For each instruction in the optimized region, Kprobes verifies that
the instruction can be executed out of line. the instruction can be executed out of line.
1.4.3 Preparing Detour Buffer Preparing Detour Buffer
^^^^^^^^^^^^^^^^^^^^^^^
Next, Kprobes prepares a "detour" buffer, which contains the following Next, Kprobes prepares a "detour" buffer, which contains the following
instruction sequence: instruction sequence:
- code to push the CPU's registers (emulating a breakpoint trap) - code to push the CPU's registers (emulating a breakpoint trap)
- a call to the trampoline code which calls user's probe handlers. - a call to the trampoline code which calls user's probe handlers.
- code to restore registers - code to restore registers
- the instructions from the optimized region - the instructions from the optimized region
- a jump back to the original execution path. - a jump back to the original execution path.
1.4.4 Pre-optimization Pre-optimization
^^^^^^^^^^^^^^^^
After preparing the detour buffer, Kprobes verifies that none of the After preparing the detour buffer, Kprobes verifies that none of the
following situations exist: following situations exist:
- The probe has either a break_handler (i.e., it's a jprobe) or a - The probe has either a break_handler (i.e., it's a jprobe) or a
post_handler. post_handler.
- Other instructions in the optimized region are probed. - Other instructions in the optimized region are probed.
- The probe is disabled. - The probe is disabled.
In any of the above cases, Kprobes won't start optimizing the probe. In any of the above cases, Kprobes won't start optimizing the probe.
Since these are temporary situations, Kprobes tries to start Since these are temporary situations, Kprobes tries to start
optimizing it again if the situation is changed. optimizing it again if the situation is changed.
@ -240,21 +261,23 @@ Kprobes returns control to the original instruction path by setting
the CPU's instruction pointer to the copied code in the detour buffer the CPU's instruction pointer to the copied code in the detour buffer
-- thus at least avoiding the single-step. -- thus at least avoiding the single-step.
1.4.5 Optimization Optimization
^^^^^^^^^^^^
The Kprobe-optimizer doesn't insert the jump instruction immediately; The Kprobe-optimizer doesn't insert the jump instruction immediately;
rather, it calls synchronize_sched() for safety first, because it's rather, it calls synchronize_sched() for safety first, because it's
possible for a CPU to be interrupted in the middle of executing the possible for a CPU to be interrupted in the middle of executing the
optimized region(*). As you know, synchronize_sched() can ensure optimized region [3]_. As you know, synchronize_sched() can ensure
that all interruptions that were active when synchronize_sched() that all interruptions that were active when synchronize_sched()
was called are done, but only if CONFIG_PREEMPT=n. So, this version was called are done, but only if CONFIG_PREEMPT=n. So, this version
of kprobe optimization supports only kernels with CONFIG_PREEMPT=n.(**) of kprobe optimization supports only kernels with CONFIG_PREEMPT=n [4]_.
After that, the Kprobe-optimizer calls stop_machine() to replace After that, the Kprobe-optimizer calls stop_machine() to replace
the optimized region with a jump instruction to the detour buffer, the optimized region with a jump instruction to the detour buffer,
using text_poke_smp(). using text_poke_smp().
1.4.6 Unoptimization Unoptimization
^^^^^^^^^^^^^^
When an optimized kprobe is unregistered, disabled, or blocked by When an optimized kprobe is unregistered, disabled, or blocked by
another kprobe, it will be unoptimized. If this happens before another kprobe, it will be unoptimized. If this happens before
@ -263,15 +286,15 @@ optimized list. If the optimization has been done, the jump is
replaced with the original code (except for an int3 breakpoint in replaced with the original code (except for an int3 breakpoint in
the first byte) by using text_poke_smp(). the first byte) by using text_poke_smp().
(*)Please imagine that the 2nd instruction is interrupted and then .. [3] Please imagine that the 2nd instruction is interrupted and then
the optimizer replaces the 2nd instruction with the jump *address* the optimizer replaces the 2nd instruction with the jump *address*
while the interrupt handler is running. When the interrupt while the interrupt handler is running. When the interrupt
returns to original address, there is no valid instruction, returns to original address, there is no valid instruction,
and it causes an unexpected result. and it causes an unexpected result.
(**)This optimization-safety checking may be replaced with the .. [4] This optimization-safety checking may be replaced with the
stop-machine method that ksplice uses for supporting a CONFIG_PREEMPT=y stop-machine method that ksplice uses for supporting a CONFIG_PREEMPT=y
kernel. kernel.
NOTE for geeks: NOTE for geeks:
The jump optimization changes the kprobe's pre_handler behavior. The jump optimization changes the kprobe's pre_handler behavior.
@ -280,11 +303,17 @@ path by changing regs->ip and returning 1. However, when the probe
is optimized, that modification is ignored. Thus, if you want to is optimized, that modification is ignored. Thus, if you want to
tweak the kernel's execution path, you need to suppress optimization, tweak the kernel's execution path, you need to suppress optimization,
using one of the following techniques: using one of the following techniques:
- Specify an empty function for the kprobe's post_handler or break_handler. - Specify an empty function for the kprobe's post_handler or break_handler.
or
or
- Execute 'sysctl -w debug.kprobes_optimization=n' - Execute 'sysctl -w debug.kprobes_optimization=n'
1.5 Blacklist .. _kprobes_blacklist:
Blacklist
---------
Kprobes can probe most of the kernel except itself. This means Kprobes can probe most of the kernel except itself. This means
that there are some functions where kprobes cannot probe. Probing that there are some functions where kprobes cannot probe. Probing
@ -297,7 +326,10 @@ to specify a blacklisted function.
Kprobes checks the given probe address against the blacklist and Kprobes checks the given probe address against the blacklist and
rejects registering it, if the given address is in the blacklist. rejects registering it, if the given address is in the blacklist.
2. Architectures Supported .. _kprobes_archs_supported:
Architectures Supported
=======================
Kprobes, jprobes, and return probes are implemented on the following Kprobes, jprobes, and return probes are implemented on the following
architectures: architectures:
@ -312,7 +344,8 @@ architectures:
- mips - mips
- s390 - s390
3. Configuring Kprobes Configuring Kprobes
===================
When configuring the kernel using make menuconfig/xconfig/oldconfig, When configuring the kernel using make menuconfig/xconfig/oldconfig,
ensure that CONFIG_KPROBES is set to "y". Under "General setup", look ensure that CONFIG_KPROBES is set to "y". Under "General setup", look
@ -331,7 +364,8 @@ it useful to "Compile the kernel with debug info" (CONFIG_DEBUG_INFO),
so you can use "objdump -d -l vmlinux" to see the source-to-object so you can use "objdump -d -l vmlinux" to see the source-to-object
code mapping. code mapping.
4. API Reference API Reference
=============
The Kprobes API includes a "register" function and an "unregister" The Kprobes API includes a "register" function and an "unregister"
function for each type of probe. The API also includes "register_*probes" function for each type of probe. The API also includes "register_*probes"
@ -340,10 +374,13 @@ Here are terse, mini-man-page specifications for these functions and
the associated probe handlers that you'll write. See the files in the the associated probe handlers that you'll write. See the files in the
samples/kprobes/ sub-directory for examples. samples/kprobes/ sub-directory for examples.
4.1 register_kprobe register_kprobe
---------------
#include <linux/kprobes.h> ::
int register_kprobe(struct kprobe *kp);
#include <linux/kprobes.h>
int register_kprobe(struct kprobe *kp);
Sets a breakpoint at the address kp->addr. When the breakpoint is Sets a breakpoint at the address kp->addr. When the breakpoint is
hit, Kprobes calls kp->pre_handler. After the probed instruction hit, Kprobes calls kp->pre_handler. After the probed instruction
@ -354,61 +391,68 @@ 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, is set KPROBE_FLAG_DISABLED, that kp will be registered but disabled,
so, its handlers aren't hit until calling enable_kprobe(kp). so, its handlers aren't hit until calling enable_kprobe(kp).
NOTE: .. 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. 1. With the introduction of the "symbol_name" field to struct kprobe,
The following will now work: the probepoint address resolution will now be taken care of by the kernel.
The following will now work::
kp.symbol_name = "symbol_name"; kp.symbol_name = "symbol_name";
(64-bit powerpc intricacies such as function descriptors are handled (64-bit powerpc intricacies such as function descriptors are handled
transparently) transparently)
2. Use the "offset" field of struct kprobe if the offset into the symbol 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 to install a probepoint is known. This field is used to calculate the
probepoint. probepoint.
3. Specify either the kprobe "symbol_name" OR the "addr". If both are 3. Specify either the kprobe "symbol_name" OR the "addr". If both are
specified, kprobe registration will fail with -EINVAL. specified, kprobe registration will fail with -EINVAL.
4. With CISC architectures (such as i386 and x86_64), the kprobes code 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. does not validate if the kprobe.addr is at an instruction boundary.
Use "offset" with caution. Use "offset" with caution.
register_kprobe() returns 0 on success, or a negative errno otherwise. register_kprobe() returns 0 on success, or a negative errno otherwise.
User's pre-handler (kp->pre_handler): User's pre-handler (kp->pre_handler)::
#include <linux/kprobes.h>
#include <linux/ptrace.h> #include <linux/kprobes.h>
int pre_handler(struct kprobe *p, struct pt_regs *regs); #include <linux/ptrace.h>
int pre_handler(struct kprobe *p, struct pt_regs *regs);
Called with p pointing to the kprobe associated with the breakpoint, Called with p pointing to the kprobe associated with the breakpoint,
and regs pointing to the struct containing the registers saved when and regs pointing to the struct containing the registers saved when
the breakpoint was hit. Return 0 here unless you're a Kprobes geek. the breakpoint was hit. Return 0 here unless you're a Kprobes geek.
User's post-handler (kp->post_handler): User's post-handler (kp->post_handler)::
#include <linux/kprobes.h>
#include <linux/ptrace.h> #include <linux/kprobes.h>
void post_handler(struct kprobe *p, struct pt_regs *regs, #include <linux/ptrace.h>
unsigned long flags); void post_handler(struct kprobe *p, struct pt_regs *regs,
unsigned long flags);
p and regs are as described for the pre_handler. flags always seems p and regs are as described for the pre_handler. flags always seems
to be zero. to be zero.
User's fault-handler (kp->fault_handler): User's fault-handler (kp->fault_handler)::
#include <linux/kprobes.h>
#include <linux/ptrace.h> #include <linux/kprobes.h>
int fault_handler(struct kprobe *p, struct pt_regs *regs, int trapnr); #include <linux/ptrace.h>
int fault_handler(struct kprobe *p, struct pt_regs *regs, int trapnr);
p and regs are as described for the pre_handler. trapnr is the p and regs are as described for the pre_handler. trapnr is the
architecture-specific trap number associated with the fault (e.g., architecture-specific trap number associated with the fault (e.g.,
on i386, 13 for a general protection fault or 14 for a page fault). on i386, 13 for a general protection fault or 14 for a page fault).
Returns 1 if it successfully handled the exception. Returns 1 if it successfully handled the exception.
4.2 register_jprobe register_jprobe
---------------
#include <linux/kprobes.h> ::
int register_jprobe(struct jprobe *jp)
#include <linux/kprobes.h>
int register_jprobe(struct jprobe *jp)
Sets a breakpoint at the address jp->kp.addr, which must be the address Sets a breakpoint at the address jp->kp.addr, which must be the address
of the first instruction of a function. When the breakpoint is hit, of the first instruction of a function. When the breakpoint is hit,
@ -423,10 +467,13 @@ declaration must match.
register_jprobe() returns 0 on success, or a negative errno otherwise. register_jprobe() returns 0 on success, or a negative errno otherwise.
4.3 register_kretprobe register_kretprobe
------------------
#include <linux/kprobes.h> ::
int register_kretprobe(struct kretprobe *rp);
#include <linux/kprobes.h>
int register_kretprobe(struct kretprobe *rp);
Establishes a return probe for the function whose address is Establishes a return probe for the function whose address is
rp->kp.addr. When that function returns, Kprobes calls rp->handler. rp->kp.addr. When that function returns, Kprobes calls rp->handler.
@ -436,14 +483,17 @@ register_kretprobe(); see "How Does a Return Probe Work?" for details.
register_kretprobe() returns 0 on success, or a negative errno register_kretprobe() returns 0 on success, or a negative errno
otherwise. otherwise.
User's return-probe handler (rp->handler): User's return-probe handler (rp->handler)::
#include <linux/kprobes.h>
#include <linux/ptrace.h> #include <linux/kprobes.h>
int kretprobe_handler(struct kretprobe_instance *ri, struct pt_regs *regs); #include <linux/ptrace.h>
int kretprobe_handler(struct kretprobe_instance *ri,
struct pt_regs *regs);
regs is as described for kprobe.pre_handler. ri points to the regs is as described for kprobe.pre_handler. ri points to the
kretprobe_instance object, of which the following fields may be kretprobe_instance object, of which the following fields may be
of interest: of interest:
- ret_addr: the return address - ret_addr: the return address
- rp: points to the corresponding kretprobe object - rp: points to the corresponding kretprobe object
- task: points to the corresponding task struct - task: points to the corresponding task struct
@ -456,74 +506,94 @@ the architecture's ABI.
The handler's return value is currently ignored. The handler's return value is currently ignored.
4.4 unregister_*probe unregister_*probe
------------------
#include <linux/kprobes.h> ::
void unregister_kprobe(struct kprobe *kp);
void unregister_jprobe(struct jprobe *jp); #include <linux/kprobes.h>
void unregister_kretprobe(struct kretprobe *rp); void unregister_kprobe(struct kprobe *kp);
void unregister_jprobe(struct jprobe *jp);
void unregister_kretprobe(struct kretprobe *rp);
Removes the specified probe. The unregister function can be called Removes the specified probe. The unregister function can be called
at any time after the probe has been registered. at any time after the probe has been registered.
NOTE: .. note::
If the functions find an incorrect probe (ex. an unregistered probe),
they clear the addr field of the probe.
4.5 register_*probes If the functions find an incorrect probe (ex. an unregistered probe),
they clear the addr field of the probe.
#include <linux/kprobes.h> register_*probes
int register_kprobes(struct kprobe **kps, int num); ----------------
int register_kretprobes(struct kretprobe **rps, int num);
int register_jprobes(struct jprobe **jps, int num); ::
#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 Registers each of the num probes in the specified array. If any
error occurs during registration, all probes in the array, up to error occurs during registration, all probes in the array, up to
the bad probe, are safely unregistered before the register_*probes the bad probe, are safely unregistered before the register_*probes
function returns. function returns.
- kps/rps/jps: an array of pointers to *probe data structures
- kps/rps/jps: an array of pointers to ``*probe`` data structures
- num: the number of the array entries. - num: the number of the array entries.
NOTE: .. 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 You have to allocate(or define) an array of pointers and set all
of the array entries before using these functions.
#include <linux/kprobes.h> unregister_*probes
void unregister_kprobes(struct kprobe **kps, int num); ------------------
void unregister_kretprobes(struct kretprobe **rps, int num);
void unregister_jprobes(struct jprobe **jps, int num); ::
#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. Removes each of the num probes in the specified array at once.
NOTE: .. 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 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.
#include <linux/kprobes.h> disable_*probe
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 ::
#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. enable_*probe(). You must specify the probe which has been registered.
4.8 enable_*probe 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 #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. the probe which has been registered.
5. Kprobes Features and Limitations Kprobes Features and Limitations
================================
Kprobes allows multiple probes at the same address. Currently, Kprobes allows multiple probes at the same address. Currently,
however, there cannot be multiple jprobes on the same function at however, there cannot be multiple jprobes on the same function at
@ -538,7 +608,7 @@ are discussed in this section.
The register_*probe functions will return -EINVAL if you attempt The register_*probe functions will return -EINVAL if you attempt
to install a probe in the code that implements Kprobes (mostly to install a probe in the code that implements Kprobes (mostly
kernel/kprobes.c and arch/*/kernel/kprobes.c, but also functions such kernel/kprobes.c and ``arch/*/kernel/kprobes.c``, but also functions such
as do_page_fault and notifier_call_chain). as do_page_fault and notifier_call_chain).
If you install a probe in an inline-able function, Kprobes makes If you install a probe in an inline-able function, Kprobes makes
@ -602,19 +672,21 @@ explain it, we introduce some terminology. Imagine a 3-instruction
sequence consisting of a two 2-byte instructions and one 3-byte sequence consisting of a two 2-byte instructions and one 3-byte
instruction. instruction.
IA ::
|
[-2][-1][0][1][2][3][4][5][6][7]
[ins1][ins2][ ins3 ]
[<- DCR ->]
[<- JTPR ->]
ins1: 1st Instruction IA
ins2: 2nd Instruction |
ins3: 3rd Instruction [-2][-1][0][1][2][3][4][5][6][7]
IA: Insertion Address [ins1][ins2][ ins3 ]
JTPR: Jump Target Prohibition Region [<- DCR ->]
DCR: Detoured Code Region [<- 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 The instructions in DCR are copied to the out-of-line buffer
of the kprobe, because the bytes in DCR are replaced by of the kprobe, because the bytes in DCR are replaced by
@ -628,7 +700,8 @@ d) DCR must not straddle the border between functions.
Anyway, these limitations are checked by the in-kernel instruction Anyway, these limitations are checked by the in-kernel instruction
decoder, so you don't need to worry about that. decoder, so you don't need to worry about that.
6. Probe Overhead Probe Overhead
==============
On a typical CPU in use in 2005, a kprobe hit takes 0.5 to 1.0 On a typical CPU in use in 2005, a kprobe hit takes 0.5 to 1.0
microseconds to process. Specifically, a benchmark that hits the same microseconds to process. Specifically, a benchmark that hits the same
@ -638,70 +711,80 @@ return-probe hit typically takes 50-75% longer than a kprobe hit.
When you have a return probe set on a function, adding a kprobe at When you have a return probe set on a function, adding a kprobe at
the entry to that function adds essentially no overhead. the entry to that function adds essentially no overhead.
Here are sample overhead figures (in usec) for different architectures. Here are sample overhead figures (in usec) for different architectures::
k = kprobe; j = jprobe; r = return probe; kr = kprobe + return probe
on same function; jr = jprobe + return probe on same function
i386: Intel Pentium M, 1495 MHz, 2957.31 bogomips k = kprobe; j = jprobe; r = return probe; kr = kprobe + return probe
k = 0.57 usec; j = 1.00; r = 0.92; kr = 0.99; jr = 1.40 on same function; jr = jprobe + return probe on same function::
x86_64: AMD Opteron 246, 1994 MHz, 3971.48 bogomips i386: Intel Pentium M, 1495 MHz, 2957.31 bogomips
k = 0.49 usec; j = 0.76; r = 0.80; kr = 0.82; jr = 1.07 k = 0.57 usec; j = 1.00; r = 0.92; kr = 0.99; jr = 1.40
ppc64: POWER5 (gr), 1656 MHz (SMT disabled, 1 virtual CPU per physical CPU) x86_64: AMD Opteron 246, 1994 MHz, 3971.48 bogomips
k = 0.77 usec; j = 1.31; r = 1.26; kr = 1.45; jr = 1.99 k = 0.49 usec; j = 0.76; r = 0.80; kr = 0.82; jr = 1.07
6.1 Optimized Probe Overhead 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
Optimized Probe Overhead
------------------------
Typically, an optimized kprobe hit takes 0.07 to 0.1 microseconds to Typically, an optimized kprobe hit takes 0.07 to 0.1 microseconds to
process. Here are sample overhead figures (in usec) for x86 architectures. 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 = unoptimized kprobe, b = boosted (single-step skipped), o = optimized kprobe,
k = 0.80 usec; b = 0.33; o = 0.05; r = 1.10; rb = 0.61; ro = 0.33 r = unoptimized kretprobe, rb = boosted kretprobe, ro = optimized kretprobe.
x86-64: Intel(R) Xeon(R) E5410, 2.33GHz, 4656.90 bogomips i386: 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 k = 0.80 usec; b = 0.33; o = 0.05; r = 1.10; rb = 0.61; ro = 0.33
7. TODO 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
TODO
====
a. SystemTap (http://sourceware.org/systemtap): Provides a simplified a. SystemTap (http://sourceware.org/systemtap): Provides a simplified
programming interface for probe-based instrumentation. Try it out. programming interface for probe-based instrumentation. Try it out.
b. Kernel return probes for sparc64. b. Kernel return probes for sparc64.
c. Support for other architectures. c. Support for other architectures.
d. User-space probes. d. User-space probes.
e. Watchpoint probes (which fire on data references). e. Watchpoint probes (which fire on data references).
8. Kprobes Example Kprobes Example
===============
See samples/kprobes/kprobe_example.c See samples/kprobes/kprobe_example.c
9. Jprobes Example Jprobes Example
===============
See samples/kprobes/jprobe_example.c See samples/kprobes/jprobe_example.c
10. Kretprobes Example Kretprobes Example
==================
See samples/kprobes/kretprobe_example.c See samples/kprobes/kretprobe_example.c
For additional information on Kprobes, refer to the following URLs: 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-106.ibm.com/developerworks/library/l-kprobes.html?ca=dgr-lnxw42Kprobe
http://www-users.cs.umn.edu/~boutcher/kprobes/ - http://www.redhat.com/magazine/005mar05/features/kprobes/
http://www.linuxsymposium.org/2006/linuxsymposium_procv2.pdf (pages 101-115) - 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 The kprobes debugfs interface
=============================
With recent kernels (> 2.6.20) the list of registered kprobes is visible 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). 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 /sys/kernel/debug/kprobes/list: Lists all registered probes on the system::
c015d71a k vfs_read+0x0 c015d71a k vfs_read+0x0
c011a316 j do_fork+0x0 c011a316 j do_fork+0x0
c03dedc5 r tcp_v4_rcv+0x0 c03dedc5 r tcp_v4_rcv+0x0
The first column provides the kernel address where the probe is inserted. The first column provides the kernel address where the probe is inserted.
The second column identifies the type of probe (k - kprobe, r - kretprobe The second column identifies the type of probe (k - kprobe, r - kretprobe
@ -725,17 +808,18 @@ 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. [DISABLED]) will be not enabled if you turn ON all kprobes by this knob.
Appendix B: The kprobes sysctl interface The kprobes sysctl interface
============================
/proc/sys/debug/kprobes-optimization: Turn kprobes optimization ON/OFF. /proc/sys/debug/kprobes-optimization: Turn kprobes optimization ON/OFF.
When CONFIG_OPTPROBES=y, this sysctl interface appears and it provides When CONFIG_OPTPROBES=y, this sysctl interface appears and it provides
a knob to globally and forcibly turn jump optimization (see section a knob to globally and forcibly turn jump optimization (see section
1.4) ON or OFF. By default, jump optimization is allowed (ON). :ref:`kprobes_jump_optimization`) ON or OFF. By default, jump optimization
If you echo "0" to this file or set "debug.kprobes_optimization" to is allowed (ON). If you echo "0" to this file or set
0 via sysctl, all optimized probes will be unoptimized, and any new "debug.kprobes_optimization" to 0 via sysctl, all optimized probes will be
probes registered after that will not be optimized. Note that this unoptimized, and any new probes registered after that will not be optimized.
knob *changes* the optimized state. This means that optimized probes Note that this knob *changes* the optimized state. This means that optimized
(marked [OPTIMIZED]) will be unoptimized ([OPTIMIZED] tag will be probes (marked [OPTIMIZED]) will be unoptimized ([OPTIMIZED] tag will be
removed). If the knob is turned on, they will be optimized again. removed). If the knob is turned on, they will be optimized again.