ABI: refuse non-matching ABI minor version on event registration
In scenarios where a lttng-tools 2.8 (lttng-ust 2.8) stack is running
and an application linked against a lttng-ust 2.7, event registration
will fail on fields size validation [1]. This is not expected based on
the ABI versioning exposed by lttng-ust 2.7 (6.0) and lttng-ust 2.8
(6.1).
The same happen if the scenario is reversed.
This is the result of a change in _ustctl_basic_type.
2.8 introduced enumeration to _ustctl_basic_type. The defined padding is
of 296 while the new union member is 312 (310 of real data + 2 for
alignment) pushing the structure size to 312 instead of the previous
296. This should have been an major ABI break but until now the problem
did not surface.
To prevent this, refuse non matching minor version. No need to check for
particular major,minor version since only 6.0 (ust 2.7) and 6.1 (ust
2.8) exist until a major ABI break.
Fix: loglevel and model_emf_uri with g++ compiled probes
Fix the loglevel and model_emf_uri features for probe providers compiled
with g++. They were previously effectless because of C++ symbol name
mangling. The weakref was refering to the non-mangled symbol, but C++
emits a mangled symbol for the static variable.
Fix this by emitting an extern "C" symbol with hidden visibility on C++.
With a C compiled, this simply turns a static variable into a variable
with hidden visibility.
Fix: perform statedump before replying to sessiond
If a stop command immediately follows a start command, the consumer
daemon will stop event recording in the ring buffers shared memory
control structures before the sessiond sends further commands to the
application. Therefore, a stop-after-start may be performed concurrently
with the statedump, leading to have parts of the statedump being
missing. This case may always happen if an application exits during
statedump, but it is not expected to have incomplete statedump in the
stop-after-start use case.
Needed if we want to hold the ust_lock() while we connect to the session
daemon without blocking the application forever if the session daemon is
hung on SIGSTOP.
This only triggers if we launchs _many_ applications with a session
daemon SIGSTOP'd (e.g. 1000 in parallel), so we fill the socket queue,
and applications hang there until the session daemon is SIGCONT'd.
Fix: perform TLS fixup in all UST entry points from each thread
Each entry point into lttng-ust that end up taking the ust lock need to
perform a TLS fixup for each thread. Add a TLS fixup in both listener
threads, in fork and base address dump helper libs, and in app context
and tracepoint probe registration/unregistration functions, which can be
called from application threads.
Those ensure we don't take the libc dl lock within the ust lock when
performing the TLS lazy fixup.
Copy Linux kernel perf_event.h installed headers into lttng-ust to know
the recent ABI layout, and use the bit description detailed in the
following Linux kernel commit:
Fall-back on the perf read system call for kernels prior to 3.12,
because older kernels have an ABI bug where a union was used for both
cap_usr_time and cap_usr_rdpmc.
Also fall-back on the perf read system call for kernels that do not
support rdpmc.
Ensure setup_perf set the pc pointer value before checking whether we
need to the file descriptor open or not.
This combines the following master commits:
* Fix: perf counters build against kernel headers < 3.12
* Add generic fallback for perf counter read
* Fix: lttng context perf: missing stdbool.h header include
* Add perf context support for ARMv7
(removed the ARM-specific lines when combining)
* Keep perf context FD open for other architectures
Since this is a bugfix, we explicitly do not enable building perf
support for other architectures, as this would introduce a feature in
the stable release cycle.
