1337072 - Implement helper routines for inspecting and breaking on mark bits

Status: RESOLVED FIXED

(Core :: JavaScript: GC, defect)

Description

[Steve Fink [:sfink] [:s:]]

Whenever I've been working with marking, it seems like I've wanted these.

Comment 1

[Steve Fink [:sfink] [:s:]]

Attachment: Implement helper routines for inspecting and breaking on mark bits

I'm not sure about the best namespace. js::gc::debug? js::gc::detail? I went for something short.

The help message should perhaps mention that it's breaking on setting a mark in that case; clearing a mark would be

  cond 7 !(*$100 & $101)

Comment 2

[Jon Coppeard (:jonco)]

Comment on attachment 8834080 [details] [diff] [review]
Implement helper routines for inspecting and breaking on mark bits

Review of attachment 8834080 [details] [diff] [review]:
-----------------------------------------------------------------

Looks good, and I'm fine with the namespace.

::: js/src/gc/Heap.h
@@ +1396,5 @@
> +
> +namespace debug {
> +
> +// Utility functions meant to be called from an interactive debugger.
> +enum class MarkColor : int {

Suggestion: this has more information than just the mark color so maybe it could be called MarkInfo or something.

@@ +1415,5 @@
> +//   $101 = 0x200000000
> +//   (gdb) watch *$100
> +//   Hardware watchpoint 7: *$100
> +//   (gdb) cond 7 *$100 & $101
> +//   (gdb) cont

Nice!

Comment 3

[Andrew McCreight [:mccr8]]

This is very handy. I was able to easily figure out two different sources of excessive unmark gray calls in bug 1336811 using it.

Comment 4

[Steve Fink [:sfink] [:s:]]

The only reason I haven't landed it is because I'm hitting a test failure with Promises where it's accessing a dead object, and I was blaming something in the stack of patches I was trying to land along with this. It's looking like it may not have been my changes in the first place, though.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/96b7a5189c50
Implement helper routines for inspecting and breaking on mark bits, r=jonco

Comment 6

[Wes Kocher (:KWierso) (Not reading bugmail; email directly if needed)]

https://hg.mozilla.org/mozilla-central/rev/96b7a5189c50