Andrew Kesterson
5eaa956f50
An unhandled error could kill the process and still report success. The default handler ended in exit(errctx->status), and an exit status is one byte wide: the kernel keeps the low 8 bits of the argument and discards the rest. Consumer statuses start at AKERR_FIRST_CONSUMER_STATUS (256), so the first status any consumer can reserve exited 0 and a shell saw a clean run. Status 300 exited 44, an unrelated error's code. There is no wider exit() to reach for. _exit(), _Exit(), quick_exit() and the raw exit_group syscall all truncate identically, and even waitid(), whose si_status is a full int, reports the truncated value -- the truncation happened before the parent looked. akerr_exit() now owns that mapping and the default handler calls it: 0 exits 0, 1 through 255 exit the status, and anything else exits AKERR_EXIT_STATUS_UNREPRESENTABLE (125) rather than a low byte that is either a lie or a claim of success. Only values that were already being delivered wrong behave differently. Call it instead of exit() anywhere you leave the process on a status; it is declared AKERR_NORETURN. akerr_exit(0) exits 0, because 0 is this library's success status. That is not a hole in the rule: PROCESS opens with case 0, which marks a zero status handled, so a successful context never reaches FINISH_NORETURN's call to the handler at all. tests/err_exit_status.c drives one table through akerr_exit() and through the default handler in forked children and requires identical exit codes, so the handler cannot grow a mapping of its own. With the clamp removed it fails with "akerr_exit(256) exited 0, want 125". The full-width status was already reaching the log and still does, which the same test asserts against the captured stack trace. 2.0.1. No ABI break: the soname stays libakerror.so.2 and nothing that already existed changed shape. akerr_exit() is a new exported symbol, so a consumer that starts calling it needs 2.0.1 at link time. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Repository Guidelines
Project Structure & Module Organization
This is a small C library built with CMake. Core implementation lives in
src/error.c. src/lock.h is private: it selects the threading backend
(pthread or none) and is not installed. The public header is generated at build
time from include/akerror.tmpl.h by scripts/generrno.sh, which also
generates src/errno.c under the build directory and stamps in whether the
build is thread safe. CMake package and pkg-config templates are in cmake/ and
akerror.pc.in. Tests are one-file C programs in tests/; shared test helpers
live beside them, such as tests/err_capture.h and tests/err_threads.h.
Build, Test, and Development Commands
Use an out-of-tree build:
cmake -S . -B build
cmake --build build
ctest --test-dir build --output-on-failure
cmake -S . -B build configures the build and generates akerror.h.
cmake --build build compiles libakerror and test executables. ctest
runs the registered unit tests. To emit CI-style results, use:
ctest --test-dir build --output-on-failure --output-junit "$(pwd)/ctest-junit.xml"
The suite includes thread tests. The run that proves there is no data race under them is ThreadSanitizer:
scripts/thread_test.sh
which configures build/tsan with -DAKERR_SANITIZE=thread, builds the library
and the tests with it, and runs CTest with ASLR disabled (TSan aborts with an
"unexpected memory mapping" on kernels with vm.mmap_rnd_bits above 28).
AKERR_SANITIZE takes any sanitizer list, so -DAKERR_SANITIZE=address,undefined
works the same way. CTest gives each test halt_on_error=1, so a report fails
the test rather than being printed and passed over — running a sanitized test
binary by hand does not inherit that. Set it yourself
(TSAN_OPTIONS=halt_on_error=1 ./build/tsan/test_err_threads_pool) or the
binary can print a race and still exit 0.
Mutation testing is available through:
cmake --build build --target mutation
scripts/mutation_test.py --target src/error.c --threshold 65
Code coverage is available through:
cmake --build build --target coverage
scripts/coverage.py --threshold 90 --branch-threshold 50
scripts/coverage.py configures its own instrumented build tree (default
build/coverage, -DAKERR_COVERAGE=ON), runs the CTest suite there, and
reports gcov line/branch coverage per library source. Thresholds gate each
file as well as the total. Coverage measures the library's own sources only --
src/error.c, src/lock.h and the generated src/errno.c; the public header's
macros expand at their call sites, so mutation testing is what checks those.
To build without threads (no locking, no thread-local storage, thread tests not
registered), configure with -DAKERR_THREADS=none. auto is the default and
fails the configure rather than falling back.
Coding Style & Naming Conventions
Use C99-compatible C and follow the surrounding style. Functions and types use
the akerr_ prefix; macros and constants use AKERR_ or all-caps macro names
such as PREPARE_ERROR. Keep generated-code changes in templates or generator
scripts, not in build outputs. Preserve concise comments for invariants,
macro constraints, and non-obvious error lifecycle behavior.
Locking. One recursive lock (akerr_state_lock, see src/lock.h) covers
both the error pool and the status registry. A function named *_locked is
called with that lock already held; a function without the suffix takes it.
Never take it in a body written with the FAIL_*_RETURN macros — those return
from the middle of the function and would skip the unlock. Split it instead: the
locked body does the work, and a thin wrapper takes the lock, calls it, and
releases it on the single return path. Do not call consumer code
(akerr_log_method, akerr_handler_unhandled_error) while holding it.
Exiting. Never call exit() with a status value. Call akerr_exit(), which
owns the one mapping from an akerr status to an exit code: an exit status is a
byte, and every consumer status starts at 256, so passing a status through
exit() silently truncates it — status 256 exits 0 and reports success. The
only exits that bypass it are the two that have no status to map, both in
src/error.c: ENSURE_ERROR_READY's pool-exhaustion abort and the NULL-context
case in akerr_default_handler_unhandled_error(). This rule applies to test
programs too, except where the test's whole point is to observe the raw
truncation.
Testing Guidelines
Add tests as tests/err_<behavior>.c. Register each new test in the
AKERR_TESTS list in CMakeLists.txt; tests that intentionally abort must
also be listed in AKERR_WILL_FAIL_TESTS. Prefer focused executable tests that
return zero on success and use existing helpers such as AKERR_CHECK. Run the
CTest suite before submitting changes, and run mutation testing and coverage
when changing core control-flow, reference counting, stack-trace, or handler
behavior.
Tests that drive the library from several threads go in the AKERR_THREAD_SAFE
branch of the AKERR_TESTS list — an -DAKERR_THREADS=none build has no
threading to test — and use tests/err_threads.h, which runs a body on
AKERR_TEST_THREADS threads that meet at a barrier first.
Count failures per thread with AKERR_TCHECK rather than returning early: a
thread that abandons its work leaves the others holding pool slots and turns one
failure into a cascade. Anything the test shares between its own threads must go
through __atomic builtins — a race in the test is still a race, and
ThreadSanitizer cannot tell you whose it is. The capturing logger in
err_capture.h is single-threaded (shared buffer, shared length); use
akerr_thread_logger instead. Run scripts/thread_test.sh when changing
anything that touches the pool, the registry, initialization, or the lock.
Commit & Pull Request Guidelines
Recent commits use short, imperative, sentence-case subjects, for example
Fix refcount leak and stack-trace buffer overflow. Keep commits focused and
describe the observable behavior changed. Pull requests should include a brief
summary, tests run, and any compatibility impact for public macros, generated
headers, installation paths, or CMake/pkg-config consumers.
Agent-Specific Instructions
Do not overwrite uncommitted user changes. Avoid editing generated files in
build/; update include/akerror.tmpl.h, src/error.c, CMake files, tests,
or scripts instead.