563000 - (JaegerDebug) JM: Debugging support

Status: RESOLVED WONTFIX

(Core :: JavaScript Engine, defect)

Description

[David Mandelin [:dmandelin]]

JM needs to support debuggers. Although it would be possible to do this by copying what TM does, and just not run in the JIT when the debugger is active, we have decided that is not a good user experience.

Instead, when a script needs to be debugged, we will recompile it in a way that allows the debugger to do everything it needs to do. We might compile it once, or maybe once for each breakpoint that is set--compilation is fast, so we have freedom. Details must be worked out later.

We also need to coordinate this with the new debug API project.

Comment 1

[Andrew Drake [:adrake]]

Attachment: Forces debug mode on.

Forces debug mode to true so firebug can be tested.

Comment 2

[Jonathan Watt [:jwatt]]

Would it be possible to provide two modes for debuggers? Could we have a normal JIT-off mode for debugging, but add an option to flick JIT back on temporarily during a JS profiling run (when presumably the user doesn't need to break or step through the code)?

(Otherwise debugger users can't really have confidence in the numbers a profile gives to provide insight into the end user experience when a debugger is not attached, and the numbers can make us look bad when everything's actually fine without the debugger attached.)

Comment 3

[Kannan Vijayan [:djvj]]

Baseline Compiler landed with debugging support.  JM debugging support is probably not in the cards.