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>
137 lines
6.4 KiB
Markdown
137 lines
6.4 KiB
Markdown
# Repository Guidelines
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## Project Structure & Module Organization
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This is a small C library built with CMake. Core implementation lives in
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`src/error.c`. `src/lock.h` is private: it selects the threading backend
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(pthread or none) and is not installed. The public header is generated at build
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time from `include/akerror.tmpl.h` by `scripts/generrno.sh`, which also
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generates `src/errno.c` under the build directory and stamps in whether the
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build is thread safe. CMake package and pkg-config templates are in `cmake/` and
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`akerror.pc.in`. Tests are one-file C programs in `tests/`; shared test helpers
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live beside them, such as `tests/err_capture.h` and `tests/err_threads.h`.
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## Build, Test, and Development Commands
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Use an out-of-tree build:
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```sh
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cmake -S . -B build
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cmake --build build
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ctest --test-dir build --output-on-failure
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```
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`cmake -S . -B build` configures the build and generates `akerror.h`.
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`cmake --build build` compiles `libakerror` and test executables. `ctest`
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runs the registered unit tests. To emit CI-style results, use:
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```sh
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ctest --test-dir build --output-on-failure --output-junit "$(pwd)/ctest-junit.xml"
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```
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The suite includes thread tests. The run that proves there is no data race under
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them is ThreadSanitizer:
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```sh
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scripts/thread_test.sh
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```
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which configures `build/tsan` with `-DAKERR_SANITIZE=thread`, builds the library
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*and* the tests with it, and runs CTest with ASLR disabled (TSan aborts with an
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"unexpected memory mapping" on kernels with `vm.mmap_rnd_bits` above 28).
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`AKERR_SANITIZE` takes any sanitizer list, so `-DAKERR_SANITIZE=address,undefined`
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works the same way. CTest gives each test `halt_on_error=1`, so a report fails
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the test rather than being printed and passed over — running a sanitized test
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binary by hand does **not** inherit that. Set it yourself
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(`TSAN_OPTIONS=halt_on_error=1 ./build/tsan/test_err_threads_pool`) or the
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binary can print a race and still exit 0.
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Mutation testing is available through:
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```sh
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cmake --build build --target mutation
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scripts/mutation_test.py --target src/error.c --threshold 65
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```
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Code coverage is available through:
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```sh
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cmake --build build --target coverage
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scripts/coverage.py --threshold 90 --branch-threshold 50
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```
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`scripts/coverage.py` configures its own instrumented build tree (default
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`build/coverage`, `-DAKERR_COVERAGE=ON`), runs the CTest suite there, and
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reports gcov line/branch coverage per library source. Thresholds gate each
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file as well as the total. Coverage measures the library's own sources only --
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`src/error.c`, `src/lock.h` and the generated `src/errno.c`; the public header's
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macros expand at their call sites, so mutation testing is what checks those.
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To build without threads (no locking, no thread-local storage, thread tests not
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registered), configure with `-DAKERR_THREADS=none`. `auto` is the default and
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fails the configure rather than falling back.
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## Coding Style & Naming Conventions
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Use C99-compatible C and follow the surrounding style. Functions and types use
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the `akerr_` prefix; macros and constants use `AKERR_` or all-caps macro names
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such as `PREPARE_ERROR`. Keep generated-code changes in templates or generator
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scripts, not in build outputs. Preserve concise comments for invariants,
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macro constraints, and non-obvious error lifecycle behavior.
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**Locking.** One recursive lock (`akerr_state_lock`, see `src/lock.h`) covers
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both the error pool and the status registry. A function named `*_locked` is
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called with that lock already held; a function without the suffix takes it.
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Never take it in a body written with the `FAIL_*_RETURN` macros — those return
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from the middle of the function and would skip the unlock. Split it instead: the
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locked body does the work, and a thin wrapper takes the lock, calls it, and
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releases it on the single return path. Do not call consumer code
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(`akerr_log_method`, `akerr_handler_unhandled_error`) while holding it.
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**Exiting.** Never call `exit()` with a status value. Call `akerr_exit()`, which
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owns the one mapping from an akerr status to an exit code: an exit status is a
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byte, and every consumer status starts at 256, so passing a status through
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`exit()` silently truncates it — status 256 exits 0 and reports success. The
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only exits that bypass it are the two that have no status to map, both in
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`src/error.c`: `ENSURE_ERROR_READY`'s pool-exhaustion abort and the NULL-context
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case in `akerr_default_handler_unhandled_error()`. This rule applies to test
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programs too, except where the test's whole point is to observe the raw
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truncation.
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## Testing Guidelines
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Add tests as `tests/err_<behavior>.c`. Register each new test in the
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`AKERR_TESTS` list in `CMakeLists.txt`; tests that intentionally abort must
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also be listed in `AKERR_WILL_FAIL_TESTS`. Prefer focused executable tests that
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return zero on success and use existing helpers such as `AKERR_CHECK`. Run the
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CTest suite before submitting changes, and run mutation testing and coverage
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when changing core control-flow, reference counting, stack-trace, or handler
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behavior.
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Tests that drive the library from several threads go in the `AKERR_THREAD_SAFE`
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branch of the `AKERR_TESTS` list — an `-DAKERR_THREADS=none` build has no
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threading to test — and use `tests/err_threads.h`, which runs a body on
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`AKERR_TEST_THREADS` threads that meet at a barrier first.
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Count failures per thread with `AKERR_TCHECK` rather than returning early: a
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thread that abandons its work leaves the others holding pool slots and turns one
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failure into a cascade. Anything the test shares between its own threads must go
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through `__atomic` builtins — a race in the test is still a race, and
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ThreadSanitizer cannot tell you whose it is. The capturing logger in
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`err_capture.h` is single-threaded (shared buffer, shared length); use
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`akerr_thread_logger` instead. Run `scripts/thread_test.sh` when changing
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anything that touches the pool, the registry, initialization, or the lock.
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## Commit & Pull Request Guidelines
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Recent commits use short, imperative, sentence-case subjects, for example
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`Fix refcount leak and stack-trace buffer overflow`. Keep commits focused and
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describe the observable behavior changed. Pull requests should include a brief
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summary, tests run, and any compatibility impact for public macros, generated
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headers, installation paths, or CMake/pkg-config consumers.
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## Agent-Specific Instructions
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Do not overwrite uncommitted user changes. Avoid editing generated files in
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`build/`; update `include/akerror.tmpl.h`, `src/error.c`, CMake files, tests,
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or scripts instead.
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