Debugging Native Android Platform Code

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Debugging Native Android Platform Code

In this document

This page contains a summary of useful tools and related commands fordebugging, tracing, and profiling native Android platform code. The pageswithin this section contain detailed information on other debugging tools foruse during development of platform-level features.

For example, you may learn how to explore system services with Dumpsys and evaluate network and RAM use. Seethe subpages for tools and methods not described below.

debuggerd

When a dynamically-linked executable starts, several signal handlers areregistered that connect todebuggerd (or debuggerd64) in the event that signalis sent to the process. Thedebuggerd process dumps registers and unwinds thestack. Here is example output (with timestamps and extraneous information removed):

*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
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

This can be pasted into development/scripts/stack to get a more detailed unwindwith line number information (assuming the unstripped binaries can be found).

Some libraries on the system are built with LOCAL_STRIP_MODULE :=keep_symbols to provide usable backtraces directly from debuggerd. This makesyour library or executable slightly larger, but not nearly as large as anunstripped version.

Note also the last line of debuggerd output --- in addition to dumping asummary to the log,debuggerd writes a full “tombstone” to disk. This containsa lot of extra information that can be helpful in debugging a crash, inparticular the stack traces for all the threads in the crashing process (notjust the thread that caught the signal) and a full memory map.

Native Debugging with GDB

Debugging a running app

To connect to an already-running app or native daemon, use gdbclient.

Current versions of gdbclient just require the process ID (PID). So to debug a process withPID 1234, simply run:

$ gdbclient 1234

The script will set up port forwarding, start the appropriategdbserver on the device, start the appropriategdb onthe host, configure gdb to find symbols, and connectgdb to the remotegdbserver.

Debugging a native process as it starts

If you want to debug a process as it starts, you’ll need to use gdbserverorgdbserver64 manually, but that’s easy too:

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

Identify the app’s PID from the gdbserver output, and then inanother window:

$ gdbclient <app pid>

Then enter continue at the gdb prompt.

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

Debugging processes that crash

If you want debuggerd to suspend crashed processes so you canattachgdb, set the appropriate property:

$ adb shell setprop debug.db.uid 999999                 # <= M
$ adb shell setprop debug.debuggerd.wait_for_gdb true   # > M

At the end of the usual crash output, debuggerd will give youinstructions on how to connectgdb using the typical command:

$ gdbclient <pid>

Debugging without symbols

If you don’t have symbols, sometimes gdb will get confused about theinstruction set it is disassembling (ARM or Thumb). The instruction set that ischosen as the default when symbol information is missing can be switchedbetween ARM or Thumb like so:

$ set arm fallback-mode arm   # or 'thumb'

Other tools

Valgrind

The following steps show you how to use Valgrind on Android. This tool suite contains anumber of tools including Memcheck for detecting memory-related errors in C andC++.

To install Valgrind, run:
```
$ mmm -j6 external/valgrind
```
Push Valgrind to the device:
```
$ adb remount
$ adb sync
```

Set up the temporary directory:

$ adb shell mkdir /data/local/tmp
$ adb shell chmod 777 /data/local/tmp

Run the system server with Valgrind:

$ adb root
$ adb shell setprop wrap.system_server "logwrapper valgrind"
$ adb shell stop && adb shell start

For debug symbols, push unstripped libraries to /data/local/symbols:

$ adb shell mkdir /data/local/symbols
$ adb push $OUT/symbols /data/local/symbols

To use Valgrind during boot up, edit out/target/product/XXXX/root/init.rc andchange:
service example /system/bin/foo --arg1 --arg2
to:
service example /system/bin/logwrapper /system/bin/valgrind /system/bin/foo --arg1 --arg2
To see the effects, you need to create a boot.img and reflash the device.