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Subject[tip:perf/core] kprobes: Hide CONFIG_OPTPROBES and set if arch supports optimized kprobes
Commit-ID:  5cc718b9dad682329a60e73547c6e708faa5bbe4
Author: Masami Hiramatsu <>
AuthorDate: Mon, 15 Mar 2010 13:00:54 -0400
Committer: Ingo Molnar <>
CommitDate: Tue, 16 Mar 2010 11:07:23 +0100

kprobes: Hide CONFIG_OPTPROBES and set if arch supports optimized kprobes

Hide CONFIG_OPTPROBES and set if the arch supports optimized
kprobes (IOW, HAVE_OPTPROBES=y), since this option doesn't
change the major behavior of kprobes, and workarounds for minor
changes are documented.

Signed-off-by: Masami Hiramatsu <>
Cc: systemtap <>
Cc: DLE <>
Cc: Dieter Ries <>
Cc: Ananth N Mavinakayanahalli <>
Cc: OGAWA Hirofumi <>
Cc: Peter Zijlstra <>
Cc: Mike Galbraith <>
Cc: Paul Mackerras <>
Cc: Arnaldo Carvalho de Melo <>
Cc: Frederic Weisbecker <>
LKML-Reference: <20100315170054.31593.3153.stgit@localhost6.localdomain6>
Signed-off-by: Ingo Molnar <>
Documentation/kprobes.txt | 10 ++--------
arch/Kconfig | 9 ++-------
2 files changed, 4 insertions(+), 15 deletions(-)

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 2f9115c..61c291c 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -165,8 +165,8 @@ the user entry_handler invocation is also skipped.

1.4 How Does Jump Optimization Work?

-If you configured your kernel with CONFIG_OPTPROBES=y (currently
-this option is supported on x86/x86-64, non-preemptive kernel) and
+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.
@@ -271,8 +271,6 @@ 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
@@ -307,10 +305,6 @@ 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
code mapping.

-If you want to reduce probing overhead, set "Kprobes jump optimization
-support" (CONFIG_OPTPROBES) to "y". You can find this option under the
-"Kprobes" line.
4. API Reference

The Kprobes API includes a "register" function and an "unregister"
diff --git a/arch/Kconfig b/arch/Kconfig
index e5eb133..f06010f 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -42,15 +42,10 @@ config KPROBES
If in doubt, say "N".

- bool "Kprobes jump optimization support (EXPERIMENTAL)"
- default y
- depends on KPROBES
+ def_bool y
depends on !PREEMPT
- depends on HAVE_OPTPROBES
- help
- This option will allow kprobes to optimize breakpoint to
- a jump for reducing its overhead.


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