Debugging with GDB
In this document
Configure debug build (from Xinshu Dong)
This is to build WebKit in debug mode. Under the Android source directory, run ‘cp
build/buildspec.mk.default buildspec.mk’. Open buildspec.mk to edit, and append the following
The current version of
envsetup.sh has a
gdbclient command that handles much of the setup. For example, to attach the already-running
globaltime application, execute the following, making sure that: 1) you do this from the same window used to build the software on the device you are debugging and 2) verify that the symbols in the object files in the build tree match up with what is installed on the device or emulator.
gdbclient app_process :5039 globaltime
gdbserver on the device and an ARM aware
arm-eabi-gdb, on the desktop machine.
- First you need to run
gdbserveron the device:
gdbserver :5039 /system/bin/executable
:5039tells gdbserver to listen on port 5039 on the localhost, which adb bridges from the host to the device.
executablerepresents the command to debug, a common one being runtime -s which starts the entire system all running in a single process.
gdbon the desktop. This can be done easily with the following command in the shell from which you built:
At this point
gdb will connect with your device and you should be able to enter
c to have the device start executing inside of the desktop
If the short instructions don’t work, these detailed instructions should:
- On the device, launch a new command:
gdbserver :5039 /system/bin/executable
or attach to an existing process:
gdbserver :5039 --attach pid
- On your workstation, forward port 5039 to the device with adb:
adb forward tcp:5039 tcp:5039
- Start a special version of
gdbthat lives in the “prebuilt” area of the source tree:
- If you can’t find either special version of
find prebuilt -name arm-eabi-gdbin your source tree to find and run the latest version:
Where product-name is the name of the device product that you’re building (for example,
sooner), and executable is the program to debug (usually
app_processfor an application).
Make sure to use the copy of the executable in the symbols directory, not the primary android directory, because the one in the primary directory has been stripped of its debugging information.
gdbwhere to find the shared libraries that will get loaded:
set solib-absolute-prefix /absolute-source-path/out/target/product/product-name/symbols set solib-search-path /absolute-source-path/out/target/product/product-name/symbols/system/lib
absolute-source-path is the path to your source tree; for example,
product-name is the same as above; for example,
Make sure you specify the correct directories—
gdbmay not tell you if you make a mistake.
- Connect to the device by issuing the
target remote :5039
gdbto connect to the localhost port 5039, which is bridged to the device by
You may need to inspire gdb to load some symbols by typing:
You should be connected and able to debug as you normally would. You can ignore the error about not finding the location for the thread creation breakpoint. It will be found when the linker loads
libc into your process before hitting
main(). Also note that the
gdb remote protocol doesn’t have a way for the device to tell the host about newly created threads so you will not always see notifications about newly created threads. Info about other threads will be queried from the device when a breakpoint is hit or you ask for it by running info thread.
Just-In-Time Debug Feature
If you see the red LED flashing it means a process is in that new state (crashed and waiting for GDB connection). If this happens to the system process, most likely your device will be frozen at this point. Do not press the home key. Bring the device to someone who can debug native crashes and ask for advice. If you’re in the field and just want your device to continue as it would have without this feature (like cylonning), press home (a tombstone will be recorded as usual). To enable a process to be debugged this way, you need to set a property:
adb shell setprop debug.db.uid 10000
and all processes with a
uid <= 10000 will be trapped in this manner. When one of them crashes, the tombstone is processed as usual, an explicit message is printed into the log, and the red LED starts flashing waiting for the Home key to be depressed (in which case it continues execution as usual).
I/DEBUG ( 27): ******************************************************** I/DEBUG ( 27): * process 82 crashed. debuggerd waiting for gdbserver I/DEBUG ( 27): * I/DEBUG ( 27): * adb shell gdbserver :port --attach 82 & I/DEBUG ( 27): * I/DEBUG ( 27): * and press the HOME key. I/DEBUG ( 27): ********************************************************
When you see the entry above, make sure
adb is forwarding port 5039 (you only need to do this once, unless the ADB server dies) and execute:
% adb forward tcp:5039 tcp:5039
Execute the line shown in the debug output, substituting 5039 for the proper
% adb shell gdbserver :5039 --attach 82 &
If the crashing process is based off zygote (that is, system_server and all applications), the default values for the
app_process binary and port
5039, are correct, so you can execute:
% cd <top of device source tree> % gdbclient
Otherwise you need to determine the path of the crashing binary and follow the steps as mentioned above (for example,
gdbclient hoser :5039 if the
hoser command has failed).