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authorMasami Hiramatsu <mhiramat@kernel.org>2018-06-20 01:16:46 +0900
committerIngo Molnar <mingo@kernel.org>2018-06-21 12:33:20 +0200
commitdcce32d952eddcd427f648ebd04339cfbf305e23 (patch)
tree921eccc1bc4a0e1b08aac07418d48fdeec0e0d4e /Documentation/kprobes.txt
parent2bbda764d720aacabaad38374d26fcccb7843f17 (diff)
Documentation/kprobes: Add how to change the execution path
Add a section that explaining how to change the execution path with kprobes and warnings for some arch. Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: linux-arch@vger.kernel.org Cc: linux-doc@vger.kernel.org Link: https://lore.kernel.org/lkml/152942500680.15209.12374262914863044775.stgit@devbox Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'Documentation/kprobes.txt')
-rw-r--r--Documentation/kprobes.txt20
1 files changed, 20 insertions, 0 deletions
diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index cbb545910634..13d8efdb9718 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -80,6 +80,26 @@ After the instruction is single-stepped, Kprobes executes the
"post_handler," if any, that is associated with the kprobe.
Execution then continues with the instruction following the probepoint.
+Changing Execution Path
+-----------------------
+
+Since the kprobes can probe into a running kernel code, it can change
+the register set, including instruction pointer. This operation
+requires maximum attention, such as keeping the stack frame, recovering
+execution path etc. Since it is operated on running kernel and need deep
+knowladge of the archtecture and concurrent computing, you can easily
+shot your foot.
+
+If you change the instruction pointer (and set up other related
+registers) in pre_handler, you must return !0 so that the kprobes
+stops single stepping and just returns to given address.
+This also means post_handler should not be called anymore.
+
+Note that this operation may be harder on some architectures which
+use TOC (Table of Contents) for function call, since you have to
+setup new TOC for your function in your module, and recover old
+one after back from it.
+
Return Probes
-------------