2017-12-14 00:18:15 +01:00
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# Android bionic status
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2017-08-28 18:18:34 +02:00
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2019-08-15 17:19:49 +02:00
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This document details libc/libm/libdl additions and behavior changes.
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See also
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[Android linker changes for NDK developers](../android-changes-for-ndk-developers.md)
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for changes related to native code loading in various Android releases.
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2017-12-14 00:18:15 +01:00
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## Bionic function availability
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2017-11-28 02:00:16 +01:00
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2017-12-14 00:18:15 +01:00
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### POSIX
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2017-11-28 02:00:16 +01:00
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2017-12-14 00:18:15 +01:00
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You can see the current status with respect to POSIX in the form of tests:
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https://android.googlesource.com/platform/bionic/+/master/tests/headers/posix/
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2017-11-28 02:00:16 +01:00
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2017-12-14 00:18:15 +01:00
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Some POSIX functionality is not supported by the Linux kernel, and
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is guarded with tests for `__linux__`. Other functionality is not
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supported by bionic or glibc, and guarded with tests for `__BIONIC__`
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and `__GLIBC__`. In other cases historical accidents mean 32-bit
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bionic diverged but 64-bit bionic matches POSIX; these are guarded with
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`__LP64__`.
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2017-11-28 02:00:16 +01:00
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2017-12-14 00:18:15 +01:00
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Most bionic-only diversions should be accompanied by an explanatory comment.
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2017-11-28 02:00:16 +01:00
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2017-12-14 00:18:15 +01:00
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Missing functions are either obsolete or explicitly disallowed by SELinux:
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* `a64l`/`l64a`
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* `confstr`
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* `crypt`/`encrypt`/`setkey`
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* `gethostid`
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* `shm_open`/`shm_unlink`
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* `sockatmark`
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2022-06-15 02:23:35 +02:00
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* `ualarm`
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2017-11-28 02:00:16 +01:00
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2017-12-14 00:18:15 +01:00
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Missing functionality:
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* `<aio.h>`
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2020-02-06 01:04:57 +01:00
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* `<monetary.h>`. See
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[discussion](https://github.com/android/ndk/issues/1182).
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2017-12-14 00:18:15 +01:00
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* `<wordexp.h>`
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2020-01-23 00:10:52 +01:00
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* Thread cancellation (`pthread_cancel`). Unlikely to ever be implemented
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because of the difficulty and cost of implementing it, and the difficulty
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of using it correctly. See
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[This is why we can't have safe cancellation points](https://lwn.net/Articles/683118/)
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for more about thread cancellation.
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2020-02-06 01:04:57 +01:00
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* Robust mutexes. See
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[discussion](https://github.com/android/ndk/issues/1181).
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2017-11-28 02:00:16 +01:00
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2017-12-14 00:18:15 +01:00
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Run `./libc/tools/check-symbols-glibc.py` in bionic/ for the current
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list of POSIX functions implemented by glibc but not by bionic.
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2017-11-28 02:00:16 +01:00
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2017-12-14 00:18:15 +01:00
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### libc
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2017-08-28 18:18:34 +02:00
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Current libc symbols: https://android.googlesource.com/platform/bionic/+/master/libc/libc.map.txt
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2022-08-02 00:18:40 +02:00
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New libc functions in U (API level 34):
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* `close_range` and `copy_file_range` (Linux-specific GNU extensions).
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New libc behavior in U (API level 34):
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* Support for `%b` and `%B` in the printf and wprintf family.
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2022-02-16 23:41:09 +01:00
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New libc functions in T (API level 33):
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2022-01-15 01:26:25 +01:00
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* `backtrace`, `backtrace_symbols`, `backtrace_symbols_fd` (`<execinfo.h>`).
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* New system call wrappers: `preadv2`, `preadv64v2`, `pwritev2`,
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`pwritev64v2`.
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New libc functions in S (API level 31):
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* New hooks for sanitizers for TLS access: `__libc_get_static_tls_bounds`,
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`__libc_register_thread_exit_callback`, `__libc_iterate_dynamic_tls`,
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`__libc_register_dynamic_tls_listeners`.
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* New helper to allow the zygote to give each zygote child its own stack
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cookie (currently unused): `android_reset_stack_guards`.
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* Non-inline symbols for `ffsl`, `ffsll`.
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* New system call wrappers: `pidfd_getfd`, `pidfd_open`, `pidfd_send_signal`,
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`process_madvise`.
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2019-04-18 23:27:24 +02:00
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New libc functions in R (API level 30):
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* Full C11 `<threads.h>` (available as inlines for older API levels).
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2020-02-22 08:21:28 +01:00
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* `memfd_create` and `mlock2` (Linux-specific GNU extensions).
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* `renameat2` and `statx` (Linux-specific GNU extensions).
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2019-08-05 23:10:17 +02:00
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* `pthread_cond_clockwait`/`pthread_mutex_clocklock`/`pthread_rwlock_clockrdlock`/`pthread_rwlock_clockwrlock`/`sem_clockwait`
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2019-04-18 23:27:24 +02:00
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2020-01-17 00:23:58 +01:00
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New libc behavior in R (API level 30):
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* [fdsan](fdsan.md) now aborts when it detects common file descriptor errors,
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rather than just logging.
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2018-08-30 23:25:32 +02:00
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New libc functions in Q (API level 29):
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2018-07-17 22:26:14 +02:00
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* `timespec_get` (C11 `<time.h>` addition)
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2018-09-18 21:52:42 +02:00
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* `reallocarray` (BSD/GNU extension in `<malloc.h>` and `<stdlib.h>`)
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2018-07-17 22:26:14 +02:00
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* `res_randomid` (in `<resolv.h>`)
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2018-09-05 21:00:55 +02:00
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* `pthread_sigqueue` (GNU extension)
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2018-10-23 20:23:00 +02:00
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* `getloadavg` (BSD/GNU extension in <stdlib.h>)
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2018-09-05 21:00:55 +02:00
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New libc behavior in Q (API level 29):
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2019-03-27 03:07:40 +01:00
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* Whole printf family now supports the GNU `%m` extension, rather than a
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special-case hack in `syslog`.
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* `popen` now always uses `O_CLOEXEC`, not just with the `e` extension.
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* Bug fixes to handling of UTF-8 U+fffe/U+ffff and code points above U+10ffff.
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* `aligned_alloc` correctly verifies that `size` is a multiple of `alignment`.
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2019-03-20 19:21:46 +01:00
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* Using `%n` with the printf family is now reported as a FORTIFY failure.
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Previous versions of Android would ignore the `%n` but not consume the
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corresponding pointer argument, leading to obscure errors. The scanf family
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is unchanged.
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2019-03-27 03:07:40 +01:00
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* Support in strptime for `%F`, `%G`, `%g`, `%P`, `%u`, `%V`, and `%v`.
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(strftime already supported them all.)
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2020-01-17 00:23:58 +01:00
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* [fdsan](fdsan.md) detects and logs common file descriptor errors at runtime.
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2018-07-17 22:26:14 +02:00
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2018-08-30 23:25:32 +02:00
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New libc functions in P (API level 28):
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2019-03-02 01:40:59 +01:00
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* `aligned_alloc`
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2017-08-28 18:18:34 +02:00
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* `__freading`/`__fwriting` (completing <stdio_ext.h>)
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2017-11-28 02:00:16 +01:00
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* `endhostent`/`endnetent`/`endprotoent`/`getnetent`/`getprotoent`/`sethostent`/`setnetent`/`setprotoent` (completing <netdb.h>)
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2017-10-19 23:35:18 +02:00
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* `fexecve`
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2017-10-31 01:47:12 +01:00
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* `fflush_unlocked`/`fgetc_unlocked`/`fgets_unlocked`/`fputc_unlocked`/`fputs_unlocked`/`fread_unlocked`/`fwrite_unlocked`
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2017-10-07 01:58:36 +02:00
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* `getentropy`/`getrandom` (adding <sys/random.h>)
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2017-08-28 18:18:34 +02:00
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* `getlogin_r`
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2017-10-07 01:58:36 +02:00
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* `glob`/`globfree` (adding <glob.h>)
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2017-11-28 02:00:16 +01:00
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* `hcreate`/`hcreate_r`/`hdestroy`/`hdestroy_r`/`hsearch`/`hsearch_r` (completing <search.h>)
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2017-08-28 18:18:34 +02:00
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* `iconv`/`iconv_close`/`iconv_open` (adding <iconv.h>)
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Implement pthread_attr_getinheritsched/pthread_attr_setinheritsched.
Historically, Android defaulted to EXPLICIT but with a special case
because SCHED_NORMAL/priority 0 was awkward. Because the code couldn't
actually tell whether SCHED_NORMAL/priority 0 was a genuine attempt to
explicitly set those attributes (because the parent thread is SCHED_FIFO,
say) or just because the pthread_attr_t was left at its defaults.
Now we support INHERIT, we could call sched_getscheduler to see whether
we actually need to call sched_setscheduler, but since the major cost
is the fixed syscall overhead, we may as well just conservatively
call sched_setscheduler and let the kernel decide whether it's a
no-op. (Especially because we'd then have to add both sched_getscheduler
and sched_setscheduler to any seccomp filter.)
Platform code (or app code that only needs to support >= P) can actually
add a call to pthread_attr_setinheritsched to say that they just want
to inherit (if they know that none of their threads actually mess with
scheduler attributes at all), which will save them a sched_setscheduler
call except in the doubly-special case of SCHED_RESET_ON_FORK (which we
do handle).
An alternative would be "make pthread_attr_setschedparams and
pthread_attr_setschedprio set EXPLICIT and change the platform default
to INHERIT", but even though I can only think of weird pathological
examples where anyone would notice that change, that behavior -- of
pthread_attr_setschedparams/pthread_attr_setschedprio overriding an
earlier call to pthread_attr_setinheritsched -- isn't allowed by POSIX
(whereas defaulting to EXPLICIT is).
If we have a lot of trouble with this change in the app compatibility
testing phase, though, we'll want to reconsider this decision!
-*-
This change also removes a comment about setting the scheduler attributes
in main_thread because we'd have to actually keep them up to date,
and it's not clear that doing so would be worth the trouble.
Also make async_safe_format_log preserve errno so we don't have to be
so careful around it.
Bug: http://b/67471710
Test: ran tests
Change-Id: Idd026c4ce78a536656adcb57aa2e7b2c616eeddf
2017-10-18 00:34:41 +02:00
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* `pthread_attr_getinheritsched`/`pthread_attr_setinheritsched`/`pthread_setschedprio`
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2018-01-26 07:50:09 +01:00
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* `pthread_mutexattr_getprotocol`/`pthread_mutexattr_setprotocol` (mutex priority inheritance)
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2018-02-01 23:21:51 +01:00
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* <signal.h> support for `sigaction64_t` and `sigset64_t` allowing LP32 access to real-time signals
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2017-10-07 01:58:36 +02:00
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* <spawn.h>
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2017-10-18 22:34:32 +02:00
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* `swab`
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2017-08-28 18:18:34 +02:00
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* `syncfs`
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2018-03-02 00:43:37 +01:00
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2018-08-30 23:25:32 +02:00
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New libc behavior in P (API level 28):
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2019-03-27 03:07:40 +01:00
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* `%C` and `%S` support in the printf family (previously only the wprintf family supported these).
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* `%mc`/`%ms`/`%m[` support in the scanf family.
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* `%s` support in strptime (strftime already supported it).
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2019-03-20 19:21:46 +01:00
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* Using a `pthread_mutex_t` after it's been destroyed will be detected at
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runtime and reported as a FORTIFY failure.
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* Passing a null `FILE*` or `DIR*` to libc is now detected at runtime and
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reported as a FORTIFY failure.
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2017-08-28 18:18:34 +02:00
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2018-08-30 23:25:32 +02:00
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New libc functions in O (API level 26):
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2017-08-28 18:18:34 +02:00
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* `sendto` FORTIFY support
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* `__system_property_read_callback`/`__system_property_wait`
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* legacy `bsd_signal`
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* `catclose`/`catgets`/`catopen` (adding <nl_types.h>)
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* `ctermid`
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* all 6 <grp.h>/<pwd.h> (get|set|end)(gr|pw)ent functions
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* `futimes`/`futimesat`/`lutimes`
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* `getdomainname`/`setdomainname`
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* `getsubopt`
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* `hasmntopt`
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* `mallopt`
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* `mblen`
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* 4 <sys/msg.h> `msg*` functions
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* <langinfo.h> `nl_langinfo`/`nl_langinfo_l`
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* `pthread_getname_np`
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* 2 new Linux system calls `quotactl` and `sync_file_range`
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* 4 <sys/sem.h> `sem*` functions
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* 4 <sys/shm.h> `shm*` functions
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* 5 legacy <signal.h> functions: `sighold`/`sigignore`/`sigpause`/`sigrelse`/`sigset`
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* `strtod_l`/`strtof_l`/`strtol_l`/`strtoul_l`
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* <wctype.h> `towctrans`/`towctrans_l`/`wctrans`/`wctrans_l`
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2019-03-20 19:21:46 +01:00
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New libc behavior in O (API level 26):
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* Passing an invalid `pthread_t` to libc is now detected at runtime and
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reported as a FORTIFY failure. Most commonly this is a result of confusing
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`pthread_t` and `pid_t`.
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2018-08-30 23:25:32 +02:00
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New libc functions in N (API level 24):
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2017-08-28 18:18:34 +02:00
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* more FORTIFY support functions (`fread`/`fwrite`/`getcwd`/`pwrite`/`write`)
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* all remaining `_FILE_OFFSET_BITS=64` functions, completing `_FILE_OFFSET_BITS=64` support in bionic (8)
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* all 7 `pthread_barrier*` functions
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* all 5 `pthread_spin*` functions
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* `lockf`/`preadv`/`pwritev`/`scandirat` and `off64_t` variants
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* `adjtimex`/`clock_adjtime`
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2018-08-30 23:25:32 +02:00
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* <ifaddrs.h> `getifaddrs`/`freeifaddrs`/`if_freenameindex`/`if_nameindex`
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2017-08-28 18:18:34 +02:00
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* `getgrgid_r`/`getgrnam_r`
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* GNU extensions `fileno_unlocked`/`strchrnul`
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* 32-bit `prlimit`
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2019-03-20 19:21:46 +01:00
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New libc behavior in N (API level 24):
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* `sem_wait` now returns EINTR when interrupted by a signal.
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2018-08-30 23:25:32 +02:00
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New libc functions in M (API level 23):
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* <dirent.h> `telldir`, `seekdir`.
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* <malloc.h> `malloc_info`.
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* <netdb.h> `gethostbyaddr_r`, `gethostbyname2_r`.
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* <pthread.h> `pthread_rwlockattr_getkind_np`/`pthread_rwlockattr_setkind_np`.
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* <pty.h> `forkpty`, `openpty`.
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* <signal.h> `sigqueue`, `sigtimedwait`, `sigwaitinfo`.
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* <stdio.h> `fmemopen`, `open_memstream`, `feof_unlocked`, `ferror_unlocked`, `clearerr_unlocked`.
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* <stdio_ext.h> `__flbf`, `__freadable`, `__fsetlocking`, `__fwritable`, `__fbufsize`, `__fpending`, `_flushlbf`, `__fpurge`.
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* <stdlib.h> `mkostemp`/`mkostemps`, `lcong48`.
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* <string.h> `basename`, `strerror_l`, `strerror_r`, `mempcpy`.
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* <sys/sysinfo.h> `get_nprocs_conf`/`get_nprocs`, `get_phys_pages`, `get_avphys_pages`.
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* <sys/uio.h> `process_vm_readv`/`process_vm_writev`.
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* `clock_getcpuclockid`, `login_tty`, `mkfifoat`, `posix_madvise`, `sethostname`, `strcasecmp_l`/`strncasecmp_l`.
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* <wchar.h> `open_wmemstream`, `wcscasecmp_l`/`wcsncasecmp_l`, `wmempcpy`.
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* all of <error.h>.
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* re-introduced various <resolv.h> functions: `ns_format_ttl`, `ns_get16`, `ns_get32`, `ns_initparse`, `ns_makecanon`, `ns_msg_getflag`, `ns_name_compress`, `ns_name_ntol`, `ns_name_ntop`, `ns_name_pack`, `ns_name_pton`, `ns_name_rollback`, `ns_name_skip`, `ns_name_uncompress`, `ns_name_unpack`, `ns_parserr`, `ns_put16`, `ns_put32`, `ns_samename`, `ns_skiprr`, `ns_sprintrr`, and `ns_sprintrrf`.
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New libc functions in L (API level 21):
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* <android/dlext.h>.
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* <android/set_abort_message.h>.
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* <arpa/inet.h> `inet_lnaof`, `inet_netof`, `inet_network`, `inet_makeaddr`.
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* <wctype.h> `iswblank`.
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* <ctype.h> `isalnum_l`, `isalpha_l`, `isblank_l`, `icntrl_l`, `isdigit_l`, `isgraph_l`, `islower_l`, `isprint_l`, `ispunct_l`, `isspace_l`, `isupper_l`, `isxdigit_l`, `_tolower`, `tolower_l`, `_toupper`, `toupper_l`.
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|
|
|
* <fcntl.h> `fallocate`, `posix_fadvise`, `posix_fallocate`, `splice`, `tee`, `vmsplice`.
|
|
|
|
|
* <inttypes.h> `wcstoimax`, `wcstoumax`.
|
|
|
|
|
* <link.h> `dl_iterate_phdr`.
|
|
|
|
|
* <mntent.h> `setmntent`, `endmntent`, `getmntent_r`.
|
|
|
|
|
* <poll.h> `ppoll`.
|
|
|
|
|
* <pthread.h> `pthread_condattr_getclock`, `pthread_condattr_setclock`, `pthread_mutex_timedlock`, `pthread_gettid_np`.
|
|
|
|
|
* <sched.h> `setns`.
|
|
|
|
|
* <search.h> `insque`, `remque`, `lfind`, `lsearch`, `twalk`.
|
|
|
|
|
* <stdio.h> `dprintf`, `vdprintf`.
|
|
|
|
|
* <stdlib.h> `initstate`, `setstate`, `getprogname`/`setprogname`, `atof`/`strtof`, `at_quick_exit`/`_Exit`/`quick_exit`, `grantpt`, `mbtowc`/`wctomb`, `posix_openpt`, `rand_r`/`rand`/`random`/`srand`/`srandom`, `strtold_l`/`strtoll_l`/`strtoull_l`.
|
|
|
|
|
* <string.h> `strcoll_l`/`strxfrm_l`, `stpcpy`/`stpncpy`.
|
|
|
|
|
* <sys/resource.h> `prlimit`.
|
|
|
|
|
* <sys/socket.h> `accept4`, `sendmmsg`.
|
|
|
|
|
* <sys/stat.h> `mkfifo`/`mknodat`.
|
|
|
|
|
* <time.h> `strftime_l`.
|
|
|
|
|
* <unistd.h> `dup3`, `execvpe`, `getpagesize`, `linkat`/`symlinkat`/`readlinkat`, `truncate`.
|
|
|
|
|
* <wchar.h> `wcstof`, `vfwscanf`/`vswscanf`/`vwscanf`, `wcstold_l`/`wcstoll`/`wcstoll_l`/`wcstoull`/`wcstoull_l`, `mbsnrtowcs`/`wcsnrtombs`, `wcscoll_l`/`wcsxfrm_l`.
|
|
|
|
|
* <wctype.h> `iswalnum_l`/`iswalpha_l`/`iswblank_l`/`iswcntrl_l`/`iswctype_l`/`iswdigit_l`/`iswgraph_l`/`iswlower_l`/`iswprint_l`/`iswpunct_l`/`iswspace_l`/`iswupper_l`/`iswxdigit_l`, `wctype_l`, `towlower_l`/`towupper_l`.
|
|
|
|
|
* all of <fts.h>.
|
|
|
|
|
* all of <locale.h>.
|
|
|
|
|
* all of <sys/epoll.h>.
|
|
|
|
|
* all of <sys/fsuid.h>.
|
|
|
|
|
* all of <sys/inotify.h>.
|
|
|
|
|
* all of <uchar.h>.
|
|
|
|
|
|
|
|
|
|
New libc functions in K (API level 19):
|
|
|
|
|
* <inttypes.h> `imaxabs`, `imaxdiv`.
|
|
|
|
|
* <stdlib.h> `abs`, `labs`, `llabs`.
|
|
|
|
|
* <sys/stat.h> `futimens`.
|
|
|
|
|
* all of <sys/statvfs.h>.
|
|
|
|
|
* all of <sys/swap.h>.
|
|
|
|
|
* all of <sys/timerfd.h>.
|
|
|
|
|
|
|
|
|
|
New libc functions in J-MR2 (API level 18):
|
|
|
|
|
* <stdio.h> `getdelim` and `getline`.
|
|
|
|
|
* <sys/auxv.h> `getauxval`.
|
|
|
|
|
* <sys/signalfd.h> `signalfd`.
|
|
|
|
|
|
|
|
|
|
New libc functions in J-MR1 (API level 17):
|
|
|
|
|
* <ftw.h>.
|
|
|
|
|
* <signal.h> `psiginfo` and `psignal`.
|
|
|
|
|
* `getsid`, `malloc_usable_size`, `mlockall`/`munlockall`, `posix_memalign`, `unshare`.
|
|
|
|
|
|
|
|
|
|
New libc functions in J (API level 16):
|
|
|
|
|
* the <search.h> tree functions `tdelete`, `tdestroy`, `tfind`, and `tsearch`.
|
|
|
|
|
* `faccessat`, `readahead`, `tgkill`.
|
|
|
|
|
* all of <sys/xattr.h>.
|
|
|
|
|
|
2017-08-28 18:18:34 +02:00
|
|
|
libc function count over time:
|
|
|
|
|
|
2019-11-13 06:06:07 +01:00
|
|
|
| OS | API level | Function count |
|
|
|
|
|
|-------|-----------|----------------|
|
|
|
|
|
| J | 16 | 842 |
|
|
|
|
|
| J MR1 | 17 | 870 |
|
|
|
|
|
| J MR2 | 18 | 878 |
|
|
|
|
|
| K | 19 | 893 |
|
|
|
|
|
| L | 21 | 1118 |
|
|
|
|
|
| M | 23 | 1183 |
|
|
|
|
|
| N | 24 | 1228 |
|
|
|
|
|
| O | 26 | 1280 |
|
|
|
|
|
| P | 28 | 1378 |
|
|
|
|
|
| Q | 29 | 1394 |
|
|
|
|
|
|
|
|
|
|
Data collected by:
|
2017-08-28 18:18:34 +02:00
|
|
|
```
|
2019-11-13 06:06:07 +01:00
|
|
|
ndk-r21$ for i in `ls -1v platforms/android-*/arch-arm/usr/lib/libc.so` ; do \
|
|
|
|
|
echo $i; nm $i | grep -w T | wc -l ; done
|
2017-08-28 18:18:34 +02:00
|
|
|
```
|
|
|
|
|
|
2017-12-14 00:18:15 +01:00
|
|
|
### libm
|
2017-08-28 18:18:34 +02:00
|
|
|
|
|
|
|
|
Current libm symbols: https://android.googlesource.com/platform/bionic/+/master/libm/libm.map.txt
|
|
|
|
|
|
2019-11-13 06:06:07 +01:00
|
|
|
0 remaining missing C11/POSIX libm functions.
|
2017-08-28 18:18:34 +02:00
|
|
|
|
2018-08-30 23:25:32 +02:00
|
|
|
New libm functions in O (API level 26):
|
|
|
|
|
* <complex.h> `clog`/`clogf`, `cpow`/`cpowf` functions.
|
|
|
|
|
|
|
|
|
|
New libm functions in M (API level 23):
|
|
|
|
|
* <complex.h> `cabs`, `carg`, `cimag`, `cacos`, `cacosh`, `casin`, `casinh`, `catan`, `catanh`, `ccos`, `ccosh`, `cexp`, `conj`, `cproj`, `csin`, `csinh`, `csqrt`, `ctan`, `ctanh`, `creal`, `cabsf`, `cargf`, `cimagf`, `cacosf`, `cacoshf`, `casinf`, `casinhf`, `catanf`, `catanhf`, `ccosf`, `ccoshf`, `cexpf`, `conjf`, `cprojf`, `csinf`, `csinhf`, `csqrtf`, `ctanf`, `ctanhf`, `crealf`, `cabsl`, `cprojl`, `csqrtl`.
|
|
|
|
|
* <math.h> `lgammal_r`.
|
|
|
|
|
|
|
|
|
|
New libm functions in L (API level 21):
|
|
|
|
|
* <complex.h> `cabsl`, `cprojl`, `csqrtl`.
|
|
|
|
|
* <math.h> `isinf`, `significandl`.
|
|
|
|
|
|
|
|
|
|
New libm functions in J-MR2 (API level 18):
|
|
|
|
|
* <math.h> `log2`, `log2f`.
|
2017-08-28 18:18:34 +02:00
|
|
|
|
2017-12-14 00:18:15 +01:00
|
|
|
|
|
|
|
|
## Target API level behavioral differences
|
|
|
|
|
|
|
|
|
|
Most bionic bug fixes and improvements have been made without checks for
|
|
|
|
|
the app's `targetSdkVersion`. As of O there were exactly two exceptions,
|
|
|
|
|
but there are likely to be more in future because of Project Treble.
|
|
|
|
|
|
|
|
|
|
### Invalid `pthread_t` handling (targetSdkVersion >= O)
|
|
|
|
|
|
|
|
|
|
As part of a long-term goal to remove the global thread list,
|
|
|
|
|
and in an attempt to flush out racy code, we changed how an invalid
|
|
|
|
|
`pthread_t` is handled. For `pthread_detach`, `pthread_getcpuclockid`,
|
|
|
|
|
`pthread_getschedparam`/`pthread_setschedparam`, `pthread_join`, and
|
|
|
|
|
`pthread_kill`, instead of returning ESRCH when passed an invalid
|
|
|
|
|
`pthread_t`, if you're targeting O or above, they'll abort with the
|
|
|
|
|
message "attempt to use invalid pthread\_t".
|
|
|
|
|
|
|
|
|
|
Note that this doesn't change behavior as much as you might think: the
|
|
|
|
|
old lookup only held the global thread list lock for the duration of
|
|
|
|
|
the lookup, so there was still a race between that and the dereference
|
|
|
|
|
in the caller, given that callers actually need the tid to pass to some
|
|
|
|
|
syscall or other, and sometimes update fields in the `pthread_internal_t`
|
|
|
|
|
struct too.
|
|
|
|
|
|
|
|
|
|
We can't check a thread's tid against 0 to see whether a `pthread_t`
|
|
|
|
|
is still valid because a dead thread gets its thread struct unmapped
|
|
|
|
|
along with its stack, so the dereference isn't safe.
|
|
|
|
|
|
|
|
|
|
To fix your code, taking the affected functions one by one:
|
|
|
|
|
|
|
|
|
|
* `pthread_getcpuclockid` and `pthread_getschedparam`/`pthread_setschedparam`
|
|
|
|
|
should be fine. Unsafe calls to those seem highly unlikely.
|
|
|
|
|
|
|
|
|
|
* Unsafe `pthread_detach` callers probably want to switch to
|
|
|
|
|
`pthread_attr_setdetachstate` instead, or use
|
|
|
|
|
`pthread_detach(pthread_self());` from the new thread's start routine
|
|
|
|
|
rather than calling detach in the parent.
|
|
|
|
|
|
|
|
|
|
* `pthread_join` calls should be safe anyway, because a joinable thread
|
|
|
|
|
won't actually exit and unmap until it's joined. If you're joining an
|
|
|
|
|
unjoinable thread, the fix is to stop marking it detached. If you're
|
|
|
|
|
joining an already-joined thread, you need to rethink your design!
|
|
|
|
|
|
|
|
|
|
* Unsafe `pthread_kill` calls aren't portably fixable. (And are obviously
|
|
|
|
|
inherently non-portable as-is.) The best alternative on Android is to
|
|
|
|
|
use `pthread_gettid_np` at some point that you know the thread to be
|
|
|
|
|
alive, and then call `kill`/`tgkill` with signal 0 (which checks
|
|
|
|
|
whether a process exists rather than actually sending a
|
|
|
|
|
signal). That's still not completely safe because if you're too late
|
|
|
|
|
the tid may have been reused, but your code is inherently unsafe without
|
|
|
|
|
a redesign anyway.
|
|
|
|
|
|
|
|
|
|
### Interruptable `sem_wait` (targetSdkVersion >= N)
|
|
|
|
|
|
|
|
|
|
POSIX says that `sem_wait` can be interrupted by delivery of a
|
|
|
|
|
signal. This wasn't historically true in Android, and when we fixed this
|
|
|
|
|
bug we found that existing code relied on the old behavior. To preserve
|
|
|
|
|
compatibility, `sem_wait` can only return EINTR on Android if the app
|
|
|
|
|
targets N or later.
|
2018-05-01 22:13:47 +02:00
|
|
|
|
|
|
|
|
|
|
|
|
|
## FORTIFY
|
|
|
|
|
|
|
|
|
|
The `_FORTIFY_SOURCE` macro can be used to enable extra
|
|
|
|
|
automatic bounds checking for common libc functions. If a buffer
|
|
|
|
|
overrun is detected, the program is safely aborted as in this
|
2019-06-28 05:42:38 +02:00
|
|
|
[example](https://source.android.com/devices/tech/debug/native-crash#fortify).
|
2018-05-01 22:13:47 +02:00
|
|
|
|
|
|
|
|
Note that in recent releases Android's FORTIFY has been extended to
|
|
|
|
|
cover other issues. It can now detect, for example, passing `O_CREAT`
|
|
|
|
|
to open(2) without specifying a mode. It also performs some checking
|
|
|
|
|
regardless of whether the caller was built with FORTIFY enabled. In P,
|
|
|
|
|
for example, calling a `pthread_mutex_` function on a destroyed mutex,
|
|
|
|
|
calling a `<dirent.h>` function on a null pointer, using `%n` with the
|
|
|
|
|
printf(3) family, or using the scanf(3) `m` modifier incorrectly will
|
|
|
|
|
all result in FORTIFY failures even for code not built with FORTIFY.
|
|
|
|
|
|
|
|
|
|
More background information is available in our
|
2019-06-28 05:42:38 +02:00
|
|
|
[FORTIFY in Android](https://android-developers.googleblog.com/2017/04/fortify-in-android.html)
|
2018-05-01 22:13:47 +02:00
|
|
|
blog post.
|
|
|
|
|
|
|
|
|
|
The Android platform is built with `-D_FORTIFY_SOURCE=2`, but NDK users
|
|
|
|
|
need to manually enable FORTIFY by setting that themselves in whatever
|
|
|
|
|
build system they're using. The exact subset of FORTIFY available to
|
|
|
|
|
NDK users will depend on their target ABI level, because when a FORTIFY
|
|
|
|
|
check can't be guaranteed at compile-time, a call to a run-time `_chk`
|
|
|
|
|
function is added.
|
