This provides a new sysprof-live-unwinder subprocess that runs as root to
allow accessing all processes on the system via /proc/$pid/. It is spawned
by sysprofd with various perf event FDs and a FD to write captures to.
Ideally the capture_fd is something that will naturally error if the client
application crashes (such as a socketpair() having the peer close). This
is not enforced but encouraged. Additionally, an event_fd is used to allow
the client application to signal the live-unwinder to exit.
Unwinding is performed by looking at the modules loaded into the target
pid and using libdwfl to access DWARF/CFI/etc state machinery. Stack data
does not touch the disk as it exists in a mmap buffer from perf and is
then translated into a callchain and sent to the Sysprof client.
Unwinding occurs as normal post-mortem though is improved through the use
of debuginfod to locate the appropriate symbols.
This is based on a debuginfod_client provided by Barnabás Pőcze in !73.
It extends it to use the new task infrastructure to elevate the download
process to the user while loading a capture file.
This simplifies deployment on embedded devices, where polkit is usually
unncessary at runtime, but pulls in quite a few otherwise unncessary
dependencies. Start to improve the situation by allowing to selectively
disable polkit-agent support at compile time, which aids in container
usage scenarios, where one wants to invoke 'sysprof-cli' from within
the container. Bypassing polkit-agent in the container is then desired,
since the host sysprofd will handle asking for permissions to enable
the tracing. It allows for a simpler setup of rootless podman
containers, avoiding UID mismatches, that lead to rejection of the
tracing enablement.
- Add a new 'polkit-agent' meson build feature, that allows to force disabling
polkit-agent support (-Dpolkit-agent=disabled).
- Mark the 'polkit-agent' feature as enabled, by default, to reflect
the current status (sysprof-cli did not build without polkit-agent support).
- libsysprof/sysprof-instrument.c: Build fix when polkit is not available,
remove the unnecessary 'g_autopr(PolkitDetails) details' variable.
- Alter the sysprof-cli dependencies to only attempt to link against
polkit-agent, if necessary. Modify sysprof-cli.c to wrap all code using
polkit-agent in HAVE_POLKIT_AGENT blocks.
This brings together the two libraries back into one now that the whole
design is pretty well sorted out. They depend on roughly the same libraries
anyway and it's way easier of the single library can both read and write
the capture files (along with bringing in libsysprof-capture symbols in
a single place).
It can be handy to get system information from journald to correlate with
what is going on in applications. This simple journald tail GSource will
dispatch to our callback which can append the logs to the capture.
This uses a custom callback rather than the GSourceFunc because that seems
a bit annoying to use with recent GCC function equivalence checks.
Being able to manage asynchronous operations with libdex will drastically
simplify how we implement the profiler and instruments. We may eventually
do the same with libsysprof-analyze to parallelize some operations.
We have a lot of twisted options, and could really use some cleanup to
make that all more manageable. I don't know anywhere we care about not
checking for a C++ compiler, so just always check for that so we can use
the demangler.
