Using Debuggers

This page details using LLDB or GDB for OS development. For app development, see Debug your app instead, which explains how to use the Android Studio GUI (based on LLDB).

GDB is deprecated and will be removed soon. If you're switching from GDB to LLDB, you should probably start by reading the LLDB Tutorial. If you're an expert GDB user, the GDB to LLDB command map is very helpful while transitioning.

Prerequisites

To use a debugger:

• Set up the build environment with the usual envsetup.sh command.
• Run the same lunch command you used when building.

For more help with setting up your environment, see Set up environment.

Debugging running apps or processes

To connect to a running app or native daemon, use gdbclient.py with a PID. For example, to debug the process with PID 1234, run this on the host:

gdbclient.py -p 1234

The script sets up port forwarding, starts the appropriate remote debugging stub on the device, starts the debugger on the host, configures it to find symbols, and connects it to the remote debugging stub.

Note: In Android 6 and lower the script was a shell script called gdbclient instead of a Python script called gdbclient.py.

Debugging native process startup

To debug a process as it starts, use gdbclient.py with the -r option. For example, to debug ls /bin, run this on the host:

gdbclient.py -r /system/bin/ls /bin

Then, enter continue at the debugger's prompt.

Debugging app startup

Sometimes you want to debug an app as it starts, such as when there's a crash and you want to step through code to see what happened before the crash. Attaching works in some cases, but in other cases is impossible because the app crashes before you can attach. The logwrapper approach (used for strace) doesn't always work because the app might not have permissions to open a port, and gdbserver inherits that restriction.

To debug app startup, use the developer options in Settings to instruct the app to wait for a Java debugger to attach:

1. Go to Settings > Developer options > Select debug app and choose your app from the list, then click Wait for debugger.
2. Start the app, either from the launcher or by using the command line to run:

   adb shell am start -a android.intent.action.MAIN -n APP_NAME/.APP_ACTIVITY
   

3. Wait for the app to load and a dialog to appear telling you the app is waiting for a debugger.
4. Attach gdbserver/gdbclient normally, set breakpoints, then continue the process.

To let the app run, attach a Java Debug Wire Protocol (JDWP) debugger such as Java Debugger (jdb):

adb forward tcp:12345 jdwp:XXX  # (Where XXX is the PID
of the debugged process.)
jdb -attach localhost:12345

Debugging apps or processes that crash

If you want debuggerd to suspend crashed processes so that you can attach a debugger, set the appropriate property:

• After Android 11

  adb shell setprop debug.debuggerd.wait_for_debugger true
  

• Android 11 and lower

  adb shell setprop debug.debuggerd.wait_for_gdb true
  

• Android 6.0 Marshmallow and lower

  adb shell setprop debug.db.uid 999999
  

At the end of the usual crash output, debuggerd provides copy and paste instructions in logcat showing how to connect the debugger to the crashed process.

Debugging without symbols

For 32-bit ARM, if you don’t have symbols, gdb can't determine which instruction set it's disassembling (ARM or Thumb). To specify the instruction set chosen as the default when symbol information is missing, set the following property:

set arm fallback-mode arm  # or thumb

Debugging with VS Code

LLDB supports debugging platform code on Visual Studio Code. You can use the VS Code debugger frontend instead of the LLDB CLI interface to control and debug native code running on devices.

Before using VS Code for debugging, install the CodeLLDB extension.

To debug code using VS Code:

1. Ensure that all build artifacts (such as symbols) required to run gdbclient.py or lldbclient.py are present.
2. Run the following command:

   lldbclient.py --setup-forwarding
         vscode-lldb ANY_OTHER_FLAGS -p pid | -n proc-name | -r ...

   This prints a JSON object and lldbclient.py continues running. This is expected; don't kill the lldbclient.py program.

   The -r flag must be the last flag if it is present due to how flags are parsed by the tool.

   Note: GDB is deprecated and LLDB should be used when possible. If GDB is required, install the C/C++ extension and add the --no-lldb flag to gdbclient.py. All other directions are identical between GDB and LLDB.
3. In the debugging tab in VS Code, select add configuration, then select LLDB: Custom Launch. This opens a launch.json file and adds a new JSON object to a list.
4. Delete the newly added debugger configuration.
5. Copy the JSON object printed by lldbclient.py and paste it into the object you just deleted. Save the changes.
6. To reload the window to refresh the debugger list, press Ctrl+Shift+P and type reload window.
7. Select the new debugger configuration and press run. The debugger should connect after 10 to 30 seconds.
8. When you're done debugging, go to the terminal running lldbclient.py and press Enter to end the lldbclient.py program.