Automating zxdb with scripts

Zxdb provides scripting support that lets you automate repetitive debugging tasks, jump to a specific application state, and verify debugger behavior in an automated way. Scripts are plain text files containing a sequence of zxdb commands alongside their expected output.

Running a script

To run a script from the command line when launching zxdb, use the -S or --script-file option.

  • Using ffx debug:
ffx debug connect -- --script-file=my_script.script
  • Or using zxdb directly (note that this will only work with offline core files, like a minidump, so your script should start by loading a core file with the opendump command. See help opendump for details.):
zxdb --script-file=my_script.script

Script syntax

Scripts are evaluated line-by-line and generally alternate between entering commands and matching lines of output.

Commands

Lines starting with [zxdb] are interpreted as commands to run. These commands are executed the same as they would be in the interactive zxdb console.

[zxdb] attach my_component.cm

You can use abbreviations and any standard zxdb features:

[zxdb] t * f

Which is equivalent to:

[zxdb] thread * frame

Output matching

If a line does not start with [zxdb] and is not a comment, it is treated as a pattern to match against the output of the previously executed command.

Because many commands in zxdb are asynchronous, the debugger needs to know when a command has actually completed its output before issuing the next one. Zxdb will wait for the output to match the specified lines before proceeding to the next command. This ensures your script stays synchronized with the debugger's asynchronous events.

[zxdb] attach cobalt.cm
Attached Process
Done.

If you don't care about the output of a command, you don't need to specify any matching lines. You can write the next [zxdb] command, and the previous command will be allowed to finish immediately.

Wildcards

If you only want to match parts of a line, or if a line contains unpredictable data (like memory addresses, process IDs, or file paths), you can use the ?? wildcard. It matches arbitrary sections of a line (up to the entire line).

[zxdb] frame
▶ 0 MyFunction() • my_file.cc:??

Comments

Lines starting with # are comments and are ignored. Comments are useful for documenting the script, but remember that UTF-8 characters are also supported.

# This is a comment explaining what the next command does.
[zxdb] pause
# Wait for the stop event
🛑

Out-of-order output

By default, the script expects output lines to arrive in the exact order specified. If the command produces output where the order is not guaranteed, you can add ## allow-out-of-order-output anywhere in the block of expected output. This ensures all the specified lines match, regardless of the order they are printed in. This directive must come immediately after the zxdb command line and before any expected output that is to be matched for the matching algorithm to correctly take into account all output.

[zxdb] thread
## allow-out-of-order-output
  1 State: Running
  2 State: Suspended

Exiting the script

Once the script completes, you will automatically be dropped into the interactive [zxdb] command line.

If you prefer zxdb to exit automatically at the end of the script instead, you can append a quit command at the end of the file. However, ensure that the previous command has matching output specified, otherwise quit might be executed before the previous command has finished.

[zxdb] quit --force

Examples

Capture async backtrace

This script attaches to a component, pauses it, prints the async backtrace, and leaves you in the interactive console to investigate further.

# Attach to the component
[zxdb] attach hwinfo.cm
Attached Process
Done.

# Pause execution
[zxdb] pause
🛑

# Output the tree of async tasks.
[zxdb] async-backtrace

This script attaches to a component, waits for it to stop, prints the backtraces of all threads, and then drops into the interactive console.

[zxdb] attach cobalt.cm
Attached Process
Done.

[zxdb] pause
🛑

# Output the backtraces of all threads of the current process.
[zxdb] thread * frame