src/devices/tech/debug/index.jd

page.title=Debugging Native Android Platform Code
@jd:body

<!--
    Copyright 2015 The Android Open Source Project

    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
    You may obtain a copy of the License at

        http://www.apache.org/licenses/LICENSE-2.0

    Unless required by applicable law or agreed to in writing, software
    distributed under the License is distributed on an "AS IS" BASIS,
    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    See the License for the specific language governing permissions and
    limitations under the License.
-->
<div id="qv-wrapper">
  <div id="qv">
    <h2>In this document</h2>
    <ol id="auto-toc"></ol>
  </div>
</div>

<p>This page contains a summary of useful tools and related commands for
debugging, tracing, and profiling native Android platform code. The pages
within this section contain detailed information on other debugging tools for
use during development of platform-level features.</p>

<p>For example, you may learn how to explore system services with <a
href="dumpsys.html">Dumpsys</a> and evaluate <a
href="netstats.html">network</a> and <a href="procstats.html">RAM</a> use. See
the subpages for tools and methods not described below.</p>

<h2 id=debuggerd>debuggerd</h2>

<p>When a dynamically-linked executable starts, several signal handlers are
registered that connect to <code>debuggerd</code> (or <code>debuggerd64)</code> in the event that signal
is sent to the process. The <code>debuggerd</code> process dumps registers and unwinds the
stack. Here is example output (with timestamps and extraneous information removed): </p>

<pre>
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Build fingerprint: 'Android/aosp_flounder/flounder:5.1.51/AOSP/enh08201009:eng/test-keys'
Revision: '0'
ABI: 'arm'
pid: 1656, tid: 1656, name: crasher  &gt;&gt;&gt; crasher &lt;&lt;&lt;
signal 6 (SIGABRT), code -6 (SI_TKILL), fault addr --------
Abort message: 'some_file.c:123: some_function: assertion "false" failed'
    r0 00000000  r1 00000678  r2 00000006  r3 f70b6dc8
    r4 f70b6dd0  r5 f70b6d80  r6 00000002  r7 0000010c
    r8 ffffffed  r9 00000000  sl 00000000  fp ff96ae1c
    ip 00000006  sp ff96ad18  lr f700ced5  pc f700dc98  cpsr 400b0010
backtrace:
    #00 pc 00042c98  /system/lib/libc.so (tgkill+12)
    #01 pc 00041ed1  /system/lib/libc.so (pthread_kill+32)
    #02 pc 0001bb87  /system/lib/libc.so (raise+10)
    #03 pc 00018cad  /system/lib/libc.so (__libc_android_abort+34)
    #04 pc 000168e8  /system/lib/libc.so (abort+4)
    #05 pc 0001a78f  /system/lib/libc.so (__libc_fatal+16)
    #06 pc 00018d35  /system/lib/libc.so (__assert2+20)
    #07 pc 00000f21  /system/xbin/crasher
    #08 pc 00016795  /system/lib/libc.so (__libc_init+44)
    #09 pc 00000abc  /system/xbin/crasher
Tombstone written to: /data/tombstones/tombstone_06
</pre>

<p>This can be pasted into <code>development/scripts/stack</code> to get a more detailed unwind
with line number information (assuming the unstripped binaries can be found).</p>

<p>Some libraries on the system are built with <code>LOCAL_STRIP_MODULE :=
keep_symbols</code> to provide usable backtraces directly from debuggerd. This makes
your library or executable slightly larger, but not nearly as large as an
unstripped version.</p>

<p>Note also the last line of <code>debuggerd</code> output --- in addition to dumping a
summary to the log, <code>debuggerd</code> writes a full “tombstone” to disk. This contains
a lot of extra information that can be helpful in debugging a crash, in
particular the stack traces for all the threads in the crashing process (not
just the thread that caught the signal) and a full memory map.</p>

<h2 id=native>Native Debugging with GDB</h2>

<h3 id=running>Debugging a running app</h3>

<p>To connect to an already-running app or native daemon, use <code>gdbclient</code>.</p>

<p>Current versions of gdbclient just require the process ID (PID). So to debug a process with
PID 1234, simply run:</p>
<pre>
$ gdbclient 1234
</pre>
<p>The script will set up port forwarding, start the appropriate
<code>gdbserver</code> on the device, start the appropriate <code>gdb</code> on
the host, configure <code>gdb</code> to find symbols, and connect
<code>gdb</code> to the remote <code>gdbserver</code>.</p>

<h3 id=starts>Debugging a native process as it starts</h3>

<p>If you want to debug a process as it starts, you’ll need to use <code>gdbserver</code>
or <code>gdbserver64</code> manually, but that’s easy too:</p>

<pre>
$ adb shell gdbserver :5039 /system/bin/<em>my_test_app</em>
Process my_test_app created; pid = 3460
Listening on port 5039
</pre>

<p>Identify the app’s PID from the <code>gdbserver</code> output, and then in
another window:</p>

<pre>
$ gdbclient <em>&lt;app pid&gt;</em>
</pre>

<p>Then enter <strong>continue</strong> at the <code>gdb</code> prompt.</p>

<p>Note that to debug a 64-bit process, you'll need to use <code>gdbserver64</code>.
The error messages from <code>gdb</code> if you made the wrong choice are unhelpful
(along the lines of <code>Reply contains invalid hex digit 59</code>).</p>

<h3 id=crash>Debugging processes that crash</h3>

<p>If you want <code>debuggerd</code> to suspend crashed processes so you can
attach <code>gdb</code>, set the appropriate property:</p>

<pre>
$ adb shell setprop debug.db.uid 999999                 # &lt;= M
$ adb shell setprop debug.debuggerd.wait_for_gdb true   # &gt; M
</pre>

<p>At the end of the usual crash output, <code>debuggerd</code> will give you
instructions on how to connect <code>gdb</code> using the typical command:
<pre>
$ gdbclient &lt;pid&gt;
</pre>

<h3 id=symbols>Debugging without symbols</h3>

<p>If you don’t have symbols, sometimes <code>gdb</code> will get confused about the
instruction set it is disassembling (ARM or Thumb). The instruction set that is
chosen as the default when symbol information is missing can be switched
between ARM or Thumb like so:</p>

<pre>
$ set arm fallback-mode arm   # or 'thumb'
</pre>

<h2 id=symbols>Other tools</h2>

<h3 id=valgrind>Valgrind</h3>

<p>The following steps show you how to use <a
href="http://valgrind.org/">Valgrind</a> on Android. This tool suite contains a
number of tools including Memcheck for detecting memory-related errors in C and
C++.</p>

<ol>
  <li>To install Valgrind, run:
<pre>
$ mmm -j6 external/valgrind
</pre>
  <li>Push Valgrind to the device:
    <br>
<pre>
$ adb remount
$ adb sync
</pre>
  <li>Set up the temporary directory:
<pre>
$ adb shell mkdir /data/local/tmp
$ adb shell chmod 777 /data/local/tmp
</pre>
  <li>Run the system server with Valgrind:
<pre>
$ adb root
$ adb shell setprop wrap.system_server "logwrapper valgrind"
$ adb shell stop && adb shell start
</pre>
  <li>For debug symbols, push unstripped libraries to <code>/data/local/symbols</code>:
<pre>
$ adb shell mkdir /data/local/symbols
$ adb push $OUT/symbols /data/local/symbols
</pre>
  <li>To use Valgrind during boot up, edit <code>out/target/product/XXXX/root/init.rc</code> and
change:<br>
<code>service example /system/bin/foo --arg1 --arg2</code><br>
to:<br>
<code>service example /system/bin/logwrapper /system/bin/valgrind /system/bin/foo --arg1 --arg2</code><br>
To see the effects, you need to create a <code>boot.img</code> and reflash the device.
</ol>

<h3 id=systrace>Systrace</h3>

<p>See <a
href="https://developer.android.com/tools/help/systrace.html">Systrace on
developer.android.com</a> for deriving execution times of applications and
other Android system processes.</p>