Documentation: tracing: Add entry argument access at function exit

[linux-2.6-block.git] / Documentation / trace / kprobetrace.rst

diff --git a/Documentation/trace/kprobetrace.rst b/Documentation/trace/kprobetrace.rst
index bf9cecb69fc9e331c3d9f2fa798b6931e009eb38..a49662ccd53cdac5eb08adc778c9c98cb826c4eb 100644 (file)
--- a/Documentation/trace/kprobetrace.rst
+++ b/Documentation/trace/kprobetrace.rst
@@ -70,6 +70,15 @@ Synopsis of kprobe_events
   (\*3) this is useful for fetching a field of data structures.
   (\*4) "u" means user-space dereference. See :ref:`user_mem_access`.
 
+Function arguments at kretprobe
+-------------------------------
+Function arguments can be accessed at kretprobe using $arg<N> fetcharg. This
+is useful to record the function parameter and return value at once, and
+trace the difference of structure fields (for debuging a function whether it
+correctly updates the given data structure or not).
+See the :ref:`sample<fprobetrace_exit_args_sample>` in fprobe event for how
+it works.
+
 .. _kprobetrace_types:
 
 Types