The name is matched against /proc/<pid>/comm, which the kernel truncates
to 15 characters. Several matches are listed so the user can pick one
with -p; a match is only accepted if /proc/<pid>/exe is readable, which
excludes zombies (they keep a comm but have no executable to map) and
inaccessible processes.
The old preflight opened one generic event, which said little about
whether the client's actual setup would work. PreflightSamplingEvent now
opens the client's exact external event shape (the per-CPU pid-filtered
CPU_CLOCK callstack event of SysTraceStart), verifies the ring mmap
works, and probes the hardware PMU counters informationally. On
EACCES/EPERM retry user-space only - both event and callchain, since the
callchain part still requires perf_allow_kernel - and report kernel
frames as unavailable; any other error is fatal, as the client's
identical shape would fail the same way.
kill(pid, 0) succeeds for zombies, so a SIGKILLed attach target whose
parent had not reaped it yet kept the monitor polling indefinitely - in
attach mode the monitor cannot reap it. Liveness now also reads the
/proc state and treats Z as dead.
- Loop startup waitpid on EINTR; kill and reap the child on fatal error
or when interrupted, instead of leaking a ptrace-stopped process.
- Treat PTRACE_DETACH failure as fatal -- otherwise the child is stuck
stopped forever.
- Zero-initialize procName so the memcpy into ___tracy_magic_process_name
does not copy uninitialized stack past the NUL.
- Forward SIGINT to the child from the signal handler when in forked
mode, so Ctrl-C during a blocking waitpid unblocks cleanly.
- Preflight perf_event_open on the target before StartupProfiler so
permission failures surface with actionable guidance instead of
silently producing no samples.
- Also handle SIGHUP and SIGQUIT.
