kprobes/docs: Remove jprobes related documents
Remove jprobes related documentation from kprobes.txt. Also add some migration advice for the people who are still using jprobes. Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com> Cc: David S . Miller <davem@davemloft.net> Cc: Ian McDonald <ian.mcdonald@jandi.co.nz> Cc: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephen Hemminger <stephen@networkplumber.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vlad Yasevich <vyasevich@gmail.com> Link: http://lkml.kernel.org/r/150724539698.5014.7300022363980503141.stgit@devbox [ Fixes to the new documentation. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Masami Hiramatsu
Ingo Molnar
Родитель
9be95bdc53
Коммит
9b17374e11
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@ -8,7 +8,7 @@ Kernel Probes (Kprobes)
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.. CONTENTS
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1. Concepts: Kprobes, Jprobes, Return Probes
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1. Concepts: Kprobes, and Return Probes
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2. Architectures Supported
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3. Configuring Kprobes
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4. API Reference
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@ -16,12 +16,12 @@ Kernel Probes (Kprobes)
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6. Probe Overhead
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7. TODO
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8. Kprobes Example
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9. Jprobes Example
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10. Kretprobes Example
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9. Kretprobes Example
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10. Deprecated Features
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Appendix A: The kprobes debugfs interface
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Appendix B: The kprobes sysctl interface
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Concepts: Kprobes, Jprobes, Return Probes
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Concepts: Kprobes and Return Probes
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=========================================
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Kprobes enables you to dynamically break into any kernel routine and
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@ -32,12 +32,10 @@ routine to be invoked when the breakpoint is hit.
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.. [1] some parts of the kernel code can not be trapped, see
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:ref:`kprobes_blacklist`)
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There are currently three types of probes: kprobes, jprobes, and
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kretprobes (also called return probes). A kprobe can be inserted
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on virtually any instruction in the kernel. A jprobe is inserted at
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the entry to a kernel function, and provides convenient access to the
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function's arguments. A return probe fires when a specified function
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returns.
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There are currently two types of probes: kprobes, and kretprobes
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(also called return probes). A kprobe can be inserted on virtually
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any instruction in the kernel. A return probe fires when a specified
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function returns.
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In the typical case, Kprobes-based instrumentation is packaged as
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a kernel module. The module's init function installs ("registers")
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@ -82,45 +80,6 @@ After the instruction is single-stepped, Kprobes executes the
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"post_handler," if any, that is associated with the kprobe.
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Execution then continues with the instruction following the probepoint.
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How Does a Jprobe Work?
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-----------------------
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A jprobe is implemented using a kprobe that is placed on a function's
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entry point. It employs a simple mirroring principle to allow
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seamless access to the probed function's arguments. The jprobe
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handler routine should have the same signature (arg list and return
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type) as the function being probed, and must always end by calling
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the Kprobes function jprobe_return().
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Here's how it works. When the probe is hit, Kprobes makes a copy of
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the saved registers and a generous portion of the stack (see below).
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Kprobes then points the saved instruction pointer at the jprobe's
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handler routine, and returns from the trap. As a result, control
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passes to the handler, which is presented with the same register and
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stack contents as the probed function. When it is done, the handler
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calls jprobe_return(), which traps again to restore the original stack
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contents and processor state and switch to the probed function.
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By convention, the callee owns its arguments, so gcc may produce code
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that unexpectedly modifies that portion of the stack. This is why
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Kprobes saves a copy of the stack and restores it after the jprobe
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handler has run. Up to MAX_STACK_SIZE bytes are copied -- e.g.,
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64 bytes on i386.
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Note that the probed function's args may be passed on the stack
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or in registers. The jprobe will work in either case, so long as the
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handler's prototype matches that of the probed function.
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Note that in some architectures (e.g.: arm64 and sparc64) the stack
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copy is not done, as the actual location of stacked parameters may be
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outside of a reasonable MAX_STACK_SIZE value and because that location
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cannot be determined by the jprobes code. In this case the jprobes
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user must be careful to make certain the calling signature of the
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function does not cause parameters to be passed on the stack (e.g.:
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more than eight function arguments, an argument of more than sixteen
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bytes, or more than 64 bytes of argument data, depending on
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architecture).
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Return Probes
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-------------
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@ -245,8 +204,7 @@ Pre-optimization
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After preparing the detour buffer, Kprobes verifies that none of the
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following situations exist:
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- The probe has either a break_handler (i.e., it's a jprobe) or a
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post_handler.
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- The probe has a post_handler.
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- Other instructions in the optimized region are probed.
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- The probe is disabled.
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@ -331,7 +289,7 @@ rejects registering it, if the given address is in the blacklist.
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Architectures Supported
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=======================
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Kprobes, jprobes, and return probes are implemented on the following
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Kprobes and return probes are implemented on the following
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architectures:
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- i386 (Supports jump optimization)
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@ -446,27 +404,6 @@ architecture-specific trap number associated with the fault (e.g.,
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on i386, 13 for a general protection fault or 14 for a page fault).
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Returns 1 if it successfully handled the exception.
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register_jprobe
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---------------
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::
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#include <linux/kprobes.h>
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int register_jprobe(struct jprobe *jp)
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Sets a breakpoint at the address jp->kp.addr, which must be the address
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of the first instruction of a function. When the breakpoint is hit,
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Kprobes runs the handler whose address is jp->entry.
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The handler should have the same arg list and return type as the probed
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function; and just before it returns, it must call jprobe_return().
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(The handler never actually returns, since jprobe_return() returns
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control to Kprobes.) If the probed function is declared asmlinkage
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or anything else that affects how args are passed, the handler's
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declaration must match.
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register_jprobe() returns 0 on success, or a negative errno otherwise.
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register_kretprobe
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------------------
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@ -513,7 +450,6 @@ unregister_*probe
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#include <linux/kprobes.h>
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void unregister_kprobe(struct kprobe *kp);
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void unregister_jprobe(struct jprobe *jp);
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void unregister_kretprobe(struct kretprobe *rp);
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Removes the specified probe. The unregister function can be called
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@ -532,7 +468,6 @@ register_*probes
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#include <linux/kprobes.h>
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int register_kprobes(struct kprobe **kps, int num);
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int register_kretprobes(struct kretprobe **rps, int num);
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int register_jprobes(struct jprobe **jps, int num);
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Registers each of the num probes in the specified array. If any
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error occurs during registration, all probes in the array, up to
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@ -555,7 +490,6 @@ unregister_*probes
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#include <linux/kprobes.h>
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void unregister_kprobes(struct kprobe **kps, int num);
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void unregister_kretprobes(struct kretprobe **rps, int num);
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void unregister_jprobes(struct jprobe **jps, int num);
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Removes each of the num probes in the specified array at once.
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@ -574,7 +508,6 @@ disable_*probe
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#include <linux/kprobes.h>
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int disable_kprobe(struct kprobe *kp);
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int disable_kretprobe(struct kretprobe *rp);
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int disable_jprobe(struct jprobe *jp);
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Temporarily disables the specified ``*probe``. You can enable it again by using
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enable_*probe(). You must specify the probe which has been registered.
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@ -587,7 +520,6 @@ enable_*probe
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#include <linux/kprobes.h>
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int enable_kprobe(struct kprobe *kp);
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int enable_kretprobe(struct kretprobe *rp);
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int enable_jprobe(struct jprobe *jp);
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Enables ``*probe`` which has been disabled by disable_*probe(). You must specify
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the probe which has been registered.
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@ -595,12 +527,10 @@ the probe which has been registered.
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Kprobes Features and Limitations
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================================
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Kprobes allows multiple probes at the same address. Currently,
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however, there cannot be multiple jprobes on the same function at
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the same time. Also, a probepoint for which there is a jprobe or
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a post_handler cannot be optimized. So if you install a jprobe,
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or a kprobe with a post_handler, at an optimized probepoint, the
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probepoint will be unoptimized automatically.
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Kprobes allows multiple probes at the same address. Also,
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a probepoint for which there is a post_handler cannot be optimized.
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So if you install a kprobe with a post_handler, at an optimized
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probepoint, the probepoint will be unoptimized automatically.
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In general, you can install a probe anywhere in the kernel.
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In particular, you can probe interrupt handlers. Known exceptions
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@ -662,7 +592,7 @@ We're unaware of other specific cases where this could be a problem.
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If, upon entry to or exit from a function, the CPU is running on
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a stack other than that of the current task, registering a return
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probe on that function may produce undesirable results. For this
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reason, Kprobes doesn't support return probes (or kprobes or jprobes)
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reason, Kprobes doesn't support return probes (or kprobes)
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on the x86_64 version of __switch_to(); the registration functions
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return -EINVAL.
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@ -706,24 +636,24 @@ Probe Overhead
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On a typical CPU in use in 2005, a kprobe hit takes 0.5 to 1.0
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microseconds to process. Specifically, a benchmark that hits the same
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probepoint repeatedly, firing a simple handler each time, reports 1-2
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million hits per second, depending on the architecture. A jprobe or
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return-probe hit typically takes 50-75% longer than a kprobe hit.
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million hits per second, depending on the architecture. A return-probe
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hit typically takes 50-75% longer than a kprobe hit.
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When you have a return probe set on a function, adding a kprobe at
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the entry to that function adds essentially no overhead.
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Here are sample overhead figures (in usec) for different architectures::
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k = kprobe; j = jprobe; r = return probe; kr = kprobe + return probe
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on same function; jr = jprobe + return probe on same function::
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k = kprobe; r = return probe; kr = kprobe + return probe
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on same function
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i386: Intel Pentium M, 1495 MHz, 2957.31 bogomips
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k = 0.57 usec; j = 1.00; r = 0.92; kr = 0.99; jr = 1.40
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k = 0.57 usec; r = 0.92; kr = 0.99
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x86_64: AMD Opteron 246, 1994 MHz, 3971.48 bogomips
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k = 0.49 usec; j = 0.76; r = 0.80; kr = 0.82; jr = 1.07
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k = 0.49 usec; r = 0.80; kr = 0.82
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ppc64: POWER5 (gr), 1656 MHz (SMT disabled, 1 virtual CPU per physical CPU)
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k = 0.77 usec; j = 1.31; r = 1.26; kr = 1.45; jr = 1.99
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k = 0.77 usec; r = 1.26; kr = 1.45
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Optimized Probe Overhead
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------------------------
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@ -755,11 +685,6 @@ Kprobes Example
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See samples/kprobes/kprobe_example.c
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Jprobes Example
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===============
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See samples/kprobes/jprobe_example.c
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Kretprobes Example
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==================
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@ -772,6 +697,37 @@ For additional information on Kprobes, refer to the following URLs:
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- http://www-users.cs.umn.edu/~boutcher/kprobes/
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- http://www.linuxsymposium.org/2006/linuxsymposium_procv2.pdf (pages 101-115)
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Deprecated Features
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===================
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Jprobes is now a deprecated feature. People who are depending on it should
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migrate to other tracing features or use older kernels. Please consider to
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migrate your tool to one of the following options:
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- Use trace-event to trace target function with arguments.
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trace-event is a low-overhead (and almost no visible overhead if it
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is off) statically defined event interface. You can define new events
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and trace it via ftrace or any other tracing tools.
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See the following urls:
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- https://lwn.net/Articles/379903/
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- https://lwn.net/Articles/381064/
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- https://lwn.net/Articles/383362/
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- Use ftrace dynamic events (kprobe event) with perf-probe.
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If you build your kernel with debug info (CONFIG_DEBUG_INFO=y), you can
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find which register/stack is assigned to which local variable or arguments
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by using perf-probe and set up new event to trace it.
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See following documents:
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- Documentation/trace/kprobetrace.txt
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- Documentation/trace/events.txt
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- tools/perf/Documentation/perf-probe.txt
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The kprobes debugfs interface
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=============================
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@ -783,14 +739,13 @@ under the /sys/kernel/debug/kprobes/ directory (assuming debugfs is mounted at /
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/sys/kernel/debug/kprobes/list: Lists all registered probes on the system::
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c015d71a k vfs_read+0x0
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c011a316 j do_fork+0x0
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c03dedc5 r tcp_v4_rcv+0x0
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The first column provides the kernel address where the probe is inserted.
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The second column identifies the type of probe (k - kprobe, r - kretprobe
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and j - jprobe), while the third column specifies the symbol+offset of
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the probe. If the probed function belongs to a module, the module name
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is also specified. Following columns show probe status. If the probe is on
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The second column identifies the type of probe (k - kprobe and r - kretprobe)
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while the third column specifies the symbol+offset of the probe.
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If the probed function belongs to a module, the module name is also
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specified. Following columns show probe status. If the probe is on
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a virtual address that is no longer valid (module init sections, module
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virtual addresses that correspond to modules that've been unloaded),
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such probes are marked with [GONE]. If the probe is temporarily disabled,
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