Unable to record pipewire/ff interaction due to shared memory use

Hello rr team!

I've written back and forth with a couple people more experienced than I about this issue (CC: @khuey), and they suggested that I open an issue here to see if one of you have a better idea of what steps we could take to debug this issue.

Currently, as part of trying to debug a crash in Firefox, I've been attempting to capture an rr trace, however because of shared memory usage inside pipewire (or between pipewire and FF?), the resulting replays are invalid and fail a rr -a.

I've tried running pipewire (and pipewire-pulse) in the same rr session as firefox by having it execute a shell script which forks them into the background prior to running FF[1], but that too fails.

The full log is attached, but the relevant snippet is:

[ERROR ./src/ReplaySession.cc:789:guard_overshoot()] Replay diverged; target registers mismatched:
[FATAL ./src/ReplaySession.cc:793:guard_overshoot()]
 (task 11716 (rec:6979) at time 104963)
 -> Assertion `false' failed to hold. overshot target ticks=43302536 by 309

[snip]

=== Start rr backtrace:
rr(_ZN2rr13dump_rr_stackEv+0x41)[0x5595af5b9311]
rr(_ZN2rr15notifying_abortEv+0xe)[0x5595af5b936e]
rr(_ZN2rr12FatalOstreamD1Ev+0x4f)[0x5595af49bdff]
rr(_ZN2rr21EmergencyDebugOstreamD2Ev+0x499)[0x5595af49c2d9]
rr(+0x17125d)[0x5595af53825d]
rr(_ZN2rr13ReplaySession20emulate_async_signalEPNS_10ReplayTaskERKNS0_15StepConstraintsElNS_15remote_code_ptrE+0x62d)[0x5595af53e04d]
rr(_ZN2rr13ReplaySession18try_one_trace_stepEPNS_10ReplayTaskERKNS0_15StepConstraintsE+0x1dc)[0x5595af53f68c]
rr(_ZN2rr13ReplaySession11replay_stepERKNS0_15StepConstraintsE+0x19e)[0x5595af53fa7e]
rr(+0x16b56e)[0x5595af53256e]
rr(_ZN2rr13ReplayCommand3runERSt6vectorINSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEESaIS7_EE+0x69d)[0x5595af533a7d]
rr(main+0x1af)[0x5595af42748f]
/lib/x86_64-linux-gnu/libc.so.6(+0x2920a)[0x7f32f4e2920a]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x7c)[0x7f32f4e292bc]
rr(_start+0x21)[0x5595af4275e1]
=== End rr backtrace

rr.log

Any suggestions for how we could capture this info?

[1]: This, essentially, boils down to pipewire &; pipewire-pulse &; firefox

Start with the attached rr.log and the replay divergence in ReplaySession::guard_overshoot and emulate_async_signal, then reproduce the pipewire/pipewire-pulse/firefox shell setup described in the issue. Done means determining whether shared memory causes the invalid replay and documenting a capture path or actionable rr failure.