External sampling opens one event per CPU for each existing thread
(attach) or per CPU (launch) per event type, so a multithreaded target
needs many fds.
TRACY_NO_CALLSTACK, TRACY_NO_SYSTEM_TRACING, TRACY_NO_SAMPLING and
TRACY_SAMPLING_PROFILER_MANUAL_START either fail to build (the external
target API lives in the callstack code) or silently produce an empty
capture (no sampling event fails, so IsSystemTracingFailed stays false).
The first three are #error'd at compile time; the TRACY_NO_SYS_TRACE /
TRACY_NO_SAMPLING environment variables are refused at startup.
A caught signal (the handlers are inherited by the child) delivered
between PTRACE_TRACEME and exec first produces a signal-delivery stop;
without handling it, the setup would run on the still pre-exec child and
capture the monitor's own image as the target's. Re-inject the caught
signal and wait again until the exec stop is reached. Job-control stops
are the exception - re-injecting SIGSTOP/SIGTSTP re-stops the child, and
PTRACE_CONT rejects a stop carrying the 0x80 job-control bit - so resume
those without a signal instead.
The client's system tracing cannot start without a tracefs (or debugfs)
mount - the tracepoint ids live under it - so starting anyway would
capture no samples.
IsSystemTracingFailed reports a SysTraceStart that the preflight could
not predict (the target exiting between the checks, the kernel rejecting
the event setup); starting anyway would capture no samples.
Polling IsDataPortListening is the only reliable check: probing the port
itself cannot distinguish the client's listener from another process
holding it.
When TRACY_PORT is not pinned the client probes 8086..8105 at startup.
Reserve the first free port up front and hand the already-bound socket
to the client via SetReservedListenSocket, so the reservation is atomic
and the reported port matches what the client listens on. A pinned
TRACY_PORT is validated like --port, since the client pins to any
nonzero value with no fallback.
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.
Delayed init was introduced 2019-02-19 in ef5e30056 and was lazy init at
that time, matching the name.
This changed 2020-05-19 in 4eb78f5c8, when auto-init was added, making
delayed init not delayed anymore.
While the option is still needed to make manual lifetime work, and it has
to be enabled on apple, there's no reason anymore to expose it to users.
- 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.
