1374248 - LUL: remove stack scanning

Status: RESOLVED FIXED

(Core :: Gecko Profiler, enhancement)

Description

[Julian Seward [:jseward]]

LUL, which currently provides native unwinding for the Gecko profiler on 32-
and 64-bit x86 Linux, has the ability to recover stack frames heuristically
using stack scanning.

Stack scanning was added in an attempt to have functional parity with the
Breakpad unwinder, which preceded LUL in this role.  However, the profiler
calls LUL with a parameter which limits the number of scan-recovered frames
to zero -- in other words it is disabled.  Previous experimentation with
stack scanning shows that it often recovers incorrect frames and so throws
unwinding off the trail completely.  It seems more suited to an
unwind-after-crash scenario -- where we want to get as much information as
we can, accepting the risk that it might be wrong -- and less suited to a
profiling scenario, where we prefer to have incomplete stacks rather than
incorrect ones.

So this bug proposes to remove stack scanning from LUL.  Given that it's
not currently used, there will be zero visible functional changes.

Comment 1

[Julian Seward [:jseward]]

Attachment: bug1374248-2.cset

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/mozilla-inbound/rev/5860160aa255
LUL: remove stack scanning.  r=njn.

Comment 3

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

https://hg.mozilla.org/mozilla-central/rev/5860160aa255