First off, this all sounds great!
I'm not on the mailing list, so apologies if this takes extra-effort to
show up there.
On 5/8/23 5:33 AM, Serhei Makarov wrote:
eu-stacktrace will be a utility to process a stream of raw stack
samples (such as those obtained from the Linux kernel's
PERF_SAMPLE_STACK facility) into a stream of stack traces (such as the
ones obtained from PERF_SAMPLE_CALLCHAIN), freeing various profiling
utilities from having to implement their own backtracing logic.
From a consumption standpoint, it would be nice if Sysprof could get a
perf stream where the PERF_SAMPLE_STACK are transparently converted to
PERF_SAMPLE_CALLCHAIN. I don't think eu-stacktrace necessarily needs to
speak Sysprof's capture API.
Sysprof already contains `sysprofd` which can open the Perf event stream
for us via d-bus/CAP_SYS_ADMIN/polkit integration. After Sysprof gets
the perf FD back from sysprofd we could spawn eu-stacktrace giving it
the FD to consume and another FD to write the translated/passthrough events.
Sysprof can do offline symbolizing of frames which is somewhat important
when trying to analyze profiles from an embedded device, a machine that
is disk/network constrained, or end-user-system via bug reports. We can
fairly trivially teach Sysprof to do symbolizing via debuginfod.
In the case you're describing, is it right that you may not be able to
unwind stack frames without debuginfod because there was no way to
locate the `.eh_frame` section for the binary?
The code to do the mount namespace conversion is quite terrible in
Sysprof and even now I'm in the midst of cleaning it up. We have to both
create a "view" of the namespace as it was to the PID as well as a way
to convert that view into something the mount namespace analyzing the
capture file might be able to open. Any of these may or may not be in a
rootless container (toolbox/podman/flatpak/etc).
Whether or not this is something we can eventually contain inside of
bubblewrap is another can of worms.
Thanks again for all your work on this, I'm very excited to see what we
can come up with!
-- Christian
