linux-kernel - [GIT PULL] tracing: Fix sample output of dynamic arrays

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Message-ID: <20150721145630.52787762@gandalf.local.home>
Date:	Tue, 21 Jul 2015 14:56:30 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, He Kuang <hekuang@...wei.com>
Subject: [GIT PULL] tracing: Fix sample output of dynamic arrays


Linus,

He Kuang noticed that the sample code using the trace_event helper
function __get_dynamic_array_len() is broken. This only changes the
sample code, and I'm pushing this now instead of later because I don't
want others using the broken code as an example when using it for real.

Please pull the latest trace-v4.2-rc2-fix2 tree, which can be found at:


  git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
trace-v4.2-rc2-fix2

Tag SHA1: a0fb8618a8d4841f2c75e9488700277f13f54394
Head SHA1: d6726c8145290bef950ae2538ea6ae1d96a1944b


Steven Rostedt (Red Hat) (1):
      tracing: Fix sample output of dynamic arrays

----
 samples/trace_events/trace-events-sample.h | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---------------------------
commit d6726c8145290bef950ae2538ea6ae1d96a1944b
Author: Steven Rostedt (Red Hat) <rostedt@...dmis.org>
Date:   Fri Jul 17 14:03:26 2015 -0400

    tracing: Fix sample output of dynamic arrays
    
    He Kuang noticed that the trace event samples for arrays was broken:
    
    "The output result of trace_foo_bar event in traceevent samples is
     wrong. This problem can be reproduced as following:
    
      (Build kernel with SAMPLE_TRACE_EVENTS=m)
    
      $ insmod trace-events-sample.ko
    
      $ echo 1 > /sys/kernel/debug/tracing/events/sample-trace/foo_bar/enable
    
      $ cat /sys/kernel/debug/tracing/trace
    
      event-sample-980 [000] ....  43.649559: foo_bar: foo hello 21 0x15
      BIT1|BIT3|0x10 {0x1,0x6f6f6e53,0xff007970,0xffffffff} Snoopy
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     The array length is not right, should be {0x1}.
      (ffffffff,ffffffff)
    
      event-sample-980 [000] ....  44.653827: foo_bar: foo hello 22 0x16
      BIT2|BIT3|0x10
      {0x1,0x2,0x646e6147,0x666c61,0xffffffff,0xffffffff,0x750aeffe,0x7}
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     The array length is not right, should be {0x1,0x2}.
      Gandalf (ffffffff,ffffffff)"
    
    This was caused by an update to have __print_array()'s second parameter
    be the count of items in the array and not the size of the array.
    
    As there is already users of __print_array(), it can not change. But
    the sample code can and we can also improve on the documentation about
    __print_array() and __get_dynamic_array_len().
    
    Link: http://lkml.kernel.org/r/1436839171-31527-2-git-send-email-hekuang@huawei.com
    
    Fixes: ac01ce1410fc2 ("tracing: Make ftrace_print_array_seq compute buf_len")
    Reported-by: He Kuang <hekuang@...wei.com>
    Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

diff --git a/samples/trace_events/trace-events-sample.h b/samples/trace_events/trace-events-sample.h
index 8965d1bb8811..125d6402f64f 100644
--- a/samples/trace_events/trace-events-sample.h
+++ b/samples/trace_events/trace-events-sample.h
@@ -168,7 +168,10 @@
  *
  *      For __dynamic_array(int, foo, bar) use __get_dynamic_array(foo)
  *            Use __get_dynamic_array_len(foo) to get the length of the array
- *            saved.
+ *            saved. Note, __get_dynamic_array_len() returns the total allocated
+ *            length of the dynamic array; __print_array() expects the second
+ *            parameter to be the number of elements. To get that, the array length
+ *            needs to be divided by the element size.
  *
  *      For __string(foo, bar) use __get_str(foo)
  *
@@ -288,7 +291,7 @@ TRACE_EVENT(foo_bar,
  *    This prints out the array that is defined by __array in a nice format.
  */
 		  __print_array(__get_dynamic_array(list),
-				__get_dynamic_array_len(list),
+				__get_dynamic_array_len(list) / sizeof(int),
 				sizeof(int)),
 		  __get_str(str), __get_bitmask(cpus))
 );
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