# Android bionic status ## Bionic function availability ### POSIX You can see the current status with respect to POSIX in the form of tests: https://android.googlesource.com/platform/bionic/+/master/tests/headers/posix/ Some POSIX functionality is not supported by the Linux kernel, and is guarded with tests for `__linux__`. Other functionality is not supported by bionic or glibc, and guarded with tests for `__BIONIC__` and `__GLIBC__`. In other cases historical accidents mean 32-bit bionic diverged but 64-bit bionic matches POSIX; these are guarded with `__LP64__`. Most bionic-only diversions should be accompanied by an explanatory comment. Missing functions are either obsolete or explicitly disallowed by SELinux: * `a64l`/`l64a` * `confstr` * `crypt`/`encrypt`/`setkey` * `gethostid` * `shm_open`/`shm_unlink` * `sockatmark` Missing functionality: * `` * `` * Thread cancellation * Robust mutexes Run `./libc/tools/check-symbols-glibc.py` in bionic/ for the current list of POSIX functions implemented by glibc but not by bionic. ### libc Current libc symbols: https://android.googlesource.com/platform/bionic/+/master/libc/libc.map.txt New libc functions in P: * `__freading`/`__fwriting` (completing ) * `endhostent`/`endnetent`/`endprotoent`/`getnetent`/`getprotoent`/`sethostent`/`setnetent`/`setprotoent` (completing ) * `fexecve` * `fflush_unlocked`/`fgetc_unlocked`/`fgets_unlocked`/`fputc_unlocked`/`fputs_unlocked`/`fread_unlocked`/`fwrite_unlocked` * `getentropy`/`getrandom` (adding ) * `getlogin_r` * `glob`/`globfree` (adding ) * `hcreate`/`hcreate_r`/`hdestroy`/`hdestroy_r`/`hsearch`/`hsearch_r` (completing ) * `iconv`/`iconv_close`/`iconv_open` (adding ) * `pthread_attr_getinheritsched`/`pthread_attr_setinheritsched`/`pthread_setschedprio` * `pthread_mutexattr_getprotocol`/`pthread_mutexattr_setprotocol` (mutex priority inheritance) * support for `sigaction64_t` and `sigset64_t` allowing LP32 access to real-time signals * * `swab` * `syncfs` New libc behavior in P: * `%C` and `%S` support in the printf family (previously only the wprintf family supported these) * `%mc`/`%ms`/`%m[` support in the scanf family * `%s` support in strptime (strftime already supported it) New libc functions in O: * `sendto` FORTIFY support * `__system_property_read_callback`/`__system_property_wait` * legacy `bsd_signal` * `catclose`/`catgets`/`catopen` (adding ) * `ctermid` * all 6 / (get|set|end)(gr|pw)ent functions * `futimes`/`futimesat`/`lutimes` * `getdomainname`/`setdomainname` * `getsubopt` * `hasmntopt` * `mallopt` * `mblen` * 4 `msg*` functions * `nl_langinfo`/`nl_langinfo_l` * `pthread_getname_np` * 2 new Linux system calls `quotactl` and `sync_file_range` * 4 `sem*` functions * 4 `shm*` functions * 5 legacy functions: `sighold`/`sigignore`/`sigpause`/`sigrelse`/`sigset` * `strtod_l`/`strtof_l`/`strtol_l`/`strtoul_l` * `towctrans`/`towctrans_l`/`wctrans`/`wctrans_l` New libc functions in N: * more FORTIFY support functions (`fread`/`fwrite`/`getcwd`/`pwrite`/`write`) * all remaining `_FILE_OFFSET_BITS=64` functions, completing `_FILE_OFFSET_BITS=64` support in bionic (8) * all 7 `pthread_barrier*` functions * all 5 `pthread_spin*` functions * `lockf`/`preadv`/`pwritev`/`scandirat` and `off64_t` variants * `adjtimex`/`clock_adjtime` * `getifaddrs`/`freeifaddrs`/`if_freenameindex`/`if_nameindex` * `getgrgid_r`/`getgrnam_r` * GNU extensions `fileno_unlocked`/`strchrnul` * 32-bit `prlimit` libc function count over time: G 803, H 825, I 826, J 846, J-MR1 873, J-MR2 881, K 896, L 1116, M 1181, N 1226, O 1278 ``` ndk-r17$ for i in `ls -1v platforms/android-*/arch-arm/usr/lib/libc.so` ; do \ echo $i; nm $i | grep -vw [AbdNnt] | grep -vw B | wc -l ; done ``` ### libm Current libm symbols: https://android.googlesource.com/platform/bionic/+/master/libm/libm.map.txt 0 remaining missing POSIX libm functions. 19 new libm functions in O: complex trig/exp/log functions. libm function count over time: G 158, J-MR2 164, L 220, M 265, O 284 ## 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.