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<html devsite>
<head>
<title>Debugging Native Android Platform Code</title>
<meta name="project_path" value="/_project.yaml" />
<meta name="book_path" value="/_book.yaml" />
</head>
<body>
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<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>The <code>debuggerd</code> process dumps registers and unwinds the
stack. 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.</p>
<p>It's possible for <code>debuggerd</code> to attach only if nothing else is
already attached. This means that using tools like <code>strace</code> or
<code>gdb</code> will prevent <code>debuggerd</code> from working. Also, if
you call <code>prctl(PR_SET_DUMPABLE, 0)</code> you can prevent
<code>debuggerd</code> from attaching. This can be useful if you wish to
explicitly opt out of crash reporting.</p>
<p>Here is example output (with timestamps and extraneous information removed):</p>
<pre class="no-pretty-print">
*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
Build fingerprint: 'Android/aosp_flounder/flounder:5.1.51/AOSP/enh08201009:eng/test-keys'
Revision: '0'
ABI: 'arm'
pid: 1656, tid: 1656, name: crasher >>> crasher <<<
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 <code>debuggerd</code>. 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>
<p>For more information about diagnosing native crashes and tombstones, see
<a href="/devices/tech/debug/native-crash.html">Diagnosing Native Crashes</a></p>
<h3>Getting a stack trace/tombstone from a running process</h3>
<p>You can also ask <code>debuggerd</code> to operate on a running process by invoking it from
the command line. Given a PID it will dump a full tombstone to stdout, or you can use
<code>-b</code> (short for <code>--backtrace</code>) to just get the stack for every thread in the
given process.
<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 class="no-pretty-print">
$ 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 class="no-pretty-print">
$ 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 class="no-pretty-print">
$ gdbclient <em><app pid></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 class="no-pretty-print">
# Android 7.0 Nougat and later.
$ adb shell setprop debug.debuggerd.wait_for_gdb true
# Android 6.0 Marshmallow and earlier.
$ adb shell setprop debug.db.uid 999999
</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 class="no-pretty-print">
$ gdbclient <pid>
</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 class="no-pretty-print">
$ 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>
<p>Android platform developers usually use
<a href="/devices/tech/debug/asan.html">AddressSanitizer (ASan)</a> rather than valgrind.</p>
<ol>
<li>To build Valgrind, run:
<pre class="no-pretty-print">
$ mmma -j6 external/valgrind
</pre>
<li>Set up the temporary directory:
<pre class="no-pretty-print">
$ adb shell mkdir /data/local/tmp
$ adb shell chmod 777 /data/local/tmp
</pre>
<li>Run the system server with Valgrind:
<pre class="no-pretty-print">
$ 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 class="no-pretty-print">
$ 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>
</body>
</html>
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