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README.md

Copyright (C) 2024, Axis Communications AB, Lund, Sweden. All Rights Reserved.

Remote debug an ACAP application

This guide will walk you through the process of debugging an ACAP application running on an Axis device using GDB and Visual Studio Code.

Project structure

The files for building the application and the debug tools are organized in the following structure.

remote-debug-example
├── .gitignore
├── app
│   ├── .devcontainer
│   │   ├── aarch64-container
│   │   │   └── devcontainer.json
│   │   └── armv7hf-container
│   │       └── devcontainer.json
│   ├── .vscode
│   │   └── launch.json
│   ├── LICENSE
│   ├── Makefile
│   ├── manifest.json
│   └── remote_debug.c
├── Dockerfile
└── README.md
  • .gitignore - gitignore file for the specific example, to avoid any build files being accidentally committed.
  • app/.devcontainer/aarch64-container/devcontainer.json - Configuration file for the aarch64 development container.
  • app/.devcontainer/armv7hf-container/devcontainer.json - Configuration file for the armv7hf development container.
  • app/.vscode/launch.json - Configuration file for the Visual Studio Code debugger.
  • app/LICENSE - Text file which lists all open source licensed source code distributed with the application.
  • app/Makefile - Makefile containing the build and link instructions for building the ACAP application with debug options added.
  • app/manifest.json - Defines the application and its configuration.
  • app/remote_debug.c - Application demonstrating a simple debugging scenario.
  • Dockerfile - Docker file with the specified Axis toolchain, API container and the additional gdbserver to build the example specified.
  • README.md - Step by step instructions on how to run the example.

Table of contents

The setup

  • Axis device (also referred to as device or target in this guide)
    • Will run gdbserver and attach to an installed ACAP application to debug.
  • User machine (also referred to as desktop in this guide)
    • Use Visual Studio Code to run gdb-multiarch and connect to the gdbserver on the device.
    • Needs access to the application binary with debug symbols (not stripped).
    • Debugging is done in a dev container (also referred to as development container and the extension is called Dev Container) in Visual Studio Code.

Prerequisites

Build and start a dev container

A dev container can be attached to Visual Studio Code and simplifies the debugging process.

Build dev container

Open a terminal, move to the example directory and run one or both of the following commands to build the dev container for the architecture of your Axis device:

docker build . --build-arg ARCH=armv7hf -t dev_container:armv7hf
docker build . --build-arg ARCH=aarch64 -t dev_container:aarch64

The dev container includes the gdbserver binary for remote debugging.

Start dev container

  1. Start Visual Studio Code and run Dev Containers: Open Folder in Container... via the Command Palette available by pressing F1 or Ctrl+Shift+P.
  2. Browse to the app folder in the repository and choose Open.
  3. In the dev container, make sure to install the recommended Visual Studio Code extensions (not the one stated in prerequisites), usually a dialog prompts the user to install recommended extensions shortly after the dev container is started. See field extensions in files app/.devcontainer/<ARCH>-container/devcontainer.json for more information.
  4. Depending on the architecture of the device you like to debug, choose the architecture of the dev container when prompted.
  5. If you don't have a terminal open by default in Visual Studio Code, open one via the Terminal → New Terminal menu.
  6. The terminal will open inside the dev container in the /opt/app directory and is now ready for development.

Build and install ACAP application

This part shows how to build and install the ACAP application of the example in the dev container started in previous section.

Build the ACAP application

To build the ACAP application, run the following command from the same terminal:

acap-build .

The /opt/app directory now contains build artifacts, where the ACAP application is found with suffix .eap and depending on which SDK architecture that was chosen, one of these files should be found:

  • remote_debug_1_0_0_aarch64.eap
  • remote_debug_1_0_0_armv7hf.eap

Note

When developing interactively in a dev container, the build files will end up in the source code directory of the repository, here called app. It's recommended to use a .gitignore file to not commit build files in a production repository. An example can be seen in the .gitignore file of this repository.

Install the ACAP application to device

To install the ACAP application on your device, make sure to enable the Allow unsigned apps toggle through the web interface and run the following command from the same terminal:

eap-install.sh <AXIS_DEVICE_IP> <ADMIN_ACCOUNT> <PASSWORD> install

Upload and start gdbserver

Before uploading the gdbserver to your device, ensure that Developer Mode is enabled. Developer Mode grants SSH access to the ACAP application's dynamic user on the Axis device.

When the ACAP application has been uploaded to your device, provided Developer Mode is enabled, an ACAP application user named acap-remote_debug with SSH access should have been created.

Make sure to set the password for the application user before continuing to next section.

Upload gdbserver to device via SCP

  1. Open a new terminal in Visual Studio Code, using either Terminal → New Terminal or Terminal → Split Terminal. This terminal will also be running inside the dev container, just like the existing terminal. Using a second terminal allows for better visualization and keeps the debugging process within the IDE.

  2. In the new terminal, upload the gdbserver binary to the Axis device directory /tmp by using scp:

    scp /opt/build/gdb/bin/gdbserver acap-remote_debug@<AXIS_DEVICE_IP>:/tmp/

Start gdbserver on device

In the same terminal (used for scp in previous section), log into the device with ssh, start the gdbserver with the application binary, and open a TCP connection to a debug port on the Axis device, here port 1234:

ssh acap-remote_debug@<AXIS_DEVICE_IP>
/tmp/gdbserver :1234 /usr/local/packages/remote_debug/remote_debug

You should see output similar to:

Process /usr/local/packages/remote_debug/remote_debug created; pid = 7423
Listening on port 1234

Tip

Keep both terminals open during the debugging process: one for building and installing the application, and one for the SSH connection to the device.

Start debugging in dev container

Note

The launch.json file contains a hardcoded IP address (192.168.0.90) for the Axis device. This usually works if the target device is connected directly to the computer, as it will typically have this IP address. However, if you are debugging a device with a different IP address, make sure to update the miDebuggerServerAddress field in launch.json with the correct IP address and port number.

  1. In the dev container, open remote_debug.c and press F5 to start debugging.

  2. You can now set breakpoints, step through the code, and inspect variables using Visual Studio Code's debugging features.

  3. In the SSH session, you should see output similar to:

    Remote debugging from host ::ffff:192.1.2.3, port 1234

To rebuild and reinstall the ACAP application after making changes, run the following commands in the dev container terminal:

make clean
acap-build .
eap-install.sh <AXIS_DEVICE_IP> <ADMIN_ACCOUNT> <PASSWORD> install

Note

If this simple example is fixed, it will run once and exit, which will also exit the gdbserver running on the Axis device. To run a new remote debug the gdbserver needs to be restarted.

Cleanup

To remove the built files and stop the debugging session:

  1. Press Shift+F5 in Visual Studio Code to stop debugging.

  2. In the dev container terminal, run the following command to remove the built files:

    make clean

Troubleshooting

  • If SSH access is not working after enabling Developer Mode, try restarting the device and then reinstall the ACAP application.
  • If SSH access is not working after upgrading the ACAP application, make sure to set the SSH password for the ACAP application user again.
  • If you encounter permission issues when uploading the gdbserver or starting the debugging session, make sure that the ACAP application user has SSH access enabled and a password set.
  • If the debugging session doesn't start, verify that the gdbserver is running on the device and listening on the correct port.
  • If you see an error message about missing debug symbols, make sure that the ACAP application was built with debug symbols and that the correct binary is being used for debugging.

License

Apache License 2.0