53 lines
1.5 KiB
Markdown
53 lines
1.5 KiB
Markdown
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# Debugging
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## Looking Glass
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[Looking Glass][lg] is a built-in debugger and inspector tool that makes
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it possible to run arbitrary JS code inside the shell, visually select
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any object from the shell's scene, and much more.
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It can be accessed by entering `lg` into the run dialog (Alt+F2).
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[lg]: looking-glass.md
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## Javascript stacktraces
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gnome-shell is split between C and JavaScript. It is sometimes necessary
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to debug the interaction between the two, for example when javascript
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code triggers a warning or crash on the C side.
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In gdb, the javascript stacktrace can be printed with
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```
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<gdb> gjs_dumpstack()
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```
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The `SHELL_DEBUG` environment variable can be used to print
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the javascript stack automatically:
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* `backtrace-warning`: when a warning is logged
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* `backtrace-segfault`: on segfaults
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To log a stacktrace when some particular javascript code is reached, you
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can insert the following code:
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```js
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console.trace('trace from doSomething()')
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```
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## Debugging the session's gnome-shell proces
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It is possible to attach gdb to the gnome-shell process of the existing
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login session (or with the native backend on a tty), but beware: When the
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debugger stops the gnome-shell process, the entire session will freeze.
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It is necessary to use a second system to continue controlling the
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debugger, most conveniently in combination with [screen]:
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1. create a screen session
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2. detach the session
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3. ssh from a second system
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4. resume the screen session
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5. attach gdb to the gnome-shell process
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[screen]: https://www.gnu.org/software/screen/
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