forked from mirrors/gecko-dev
8f22036232
r? @jdm (or anyone else) Source-Repo: https://github.com/servo/servo Source-Revision: bfd4a0e5ffce6ceed6c4426279a8f3dcb3766fd1
70 lines
1.9 KiB
Markdown
70 lines
1.9 KiB
Markdown
# Servo debugging guide
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There are a few ways to debug Servo. `mach` supports a `--debug` flag that
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searches a suitable debugger for you and runs servo with the appropriate
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arguments under it:
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```
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./mach run --debug test.html
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```
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You can also specify an alternative debugger using the `--debugger` flag:
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```
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./mach run --debugger=my-debugger test.html
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```
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You can also, of course, run directly your debugger on the Servo binary:
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```
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$ gdb --args ./target/debug/servo test.html
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```
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## Debugging SpiderMonkey.
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You can build Servo with a debug version of SpiderMonkey passing the
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`--debug-mozjs` flag to `./mach build`.
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Note that this sometimes can cause problems when an existing build exists, so
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you might have to delete the `mozjs` build directory, or run `./mach clean`
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before your first `--debug-mozjs` build.
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## Debugging Servo with [rr][rr].
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To record a trace under rr you can either use:
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```
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$ ./mach run --debugger=rr testcase.html
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```
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Or:
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```
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$ rr record ./target/debug/servo testcase.html
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```
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### Running WPT tests under rr's chaos mode.
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Matt added a mode to Servo's testing commands to record traces of Servo running
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a test or set of tests until the result is unexpected.
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To use this, you can pass the `--chaos` argument to `mach test-wpt`:
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```
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$ ./mach test-wpt --chaos path/to/test
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```
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Note that for this to work you need to have `rr` in your `PATH`.
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Also, note that this might generate a lot of traces, so you might want to delete
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them when you're done. They're under `$HOME/.local/share/rr`.
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### Known gotchas
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If you use a Haswell processor that supports Hardware Lock Ellision, rr might
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not work for you. There's a `rr` [bug][rr-bug] open about this. Until that gets
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fixed, you can ensure that the `parking_lot` dependency isn't built with the
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`nightly` feature, which as of this writing is the only dependency that uses it.
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[rr]: http://rr-project.org/
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[rr-bug]: https://github.com/mozilla/rr/issues/1883
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