V8 Key Commands

Use this skill to find the correct commands for common development tasks in V8. This unifies the commands listed in workspace configuration and ensures consistent usage.

Building

V8 uses gm.py as a wrapper around GN and Ninja for building.

• Build (Debug): tools/dev/gm.py quiet x64.debug tests
• Build (Optimized Debug): tools/dev/gm.py quiet x64.optdebug tests
• Build (Release): tools/dev/gm.py quiet x64.release tests
• Sync DEPS Options: Use tools/dev/gm.py quiet x64.optdebug.d8 --sync to sync DEPS when switching between branches. Use the slower --sync=force option if there are still issues with broken DEPS.

Note: Always pass the quiet keyword unless told otherwise to avoid excessive output.

Debugging

Run d8 with GDB or LLDB for native code debugging.

# Example of running d8 with gdb
gdb --args out/x64.debug/d8 --my-flag my-script.js

Common Diagnostic Flags

• --trace-opt: Log optimized functions.
• --trace-deopt: Log when and why functions are deoptimized.
• --trace-gc: Log garbage collection events.
• --allow-natives-syntax: Enables calling of internal V8 functions (e.g., %OptimizeFunctionOnNextCall(f)) from JavaScript for testing purposes.
• --gdbjit: Allows seeing Maglev graphs or JavaScript code in GDB backtraces. To debug issues involving code motion disable gdbjit (as it disables code motion).

A comprehensive list of all flags can be found by running out/x64.debug/d8 --help.

Testing

For detailed instructions on running tests and interpreting failures, see the dedicated test execution guidelines.

Key commands summary:

• Run tests: tools/run-tests.py --progress dots --outdir=out/x64.optdebug