| # 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: |
| * `<aio.h>` |
| * `<wordexp.h>` |
| * 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 <stdio_ext.h>) |
| * `endhostent`/`endnetent`/`endprotoent`/`getnetent`/`getprotoent`/`sethostent`/`setnetent`/`setprotoent` (completing <netdb.h>) |
| * `fexecve` |
| * `fflush_unlocked`/`fgetc_unlocked`/`fgets_unlocked`/`fputc_unlocked`/`fputs_unlocked`/`fread_unlocked`/`fwrite_unlocked` |
| * `getentropy`/`getrandom` (adding <sys/random.h>) |
| * `getlogin_r` |
| * `glob`/`globfree` (adding <glob.h>) |
| * `hcreate`/`hcreate_r`/`hdestroy`/`hdestroy_r`/`hsearch`/`hsearch_r` (completing <search.h>) |
| * `iconv`/`iconv_close`/`iconv_open` (adding <iconv.h>) |
| * `pthread_attr_getinheritsched`/`pthread_attr_setinheritsched`/`pthread_setschedprio` |
| * `pthread_mutexattr_getprotocol`/`pthread_mutexattr_setprotocol` (mutex priority inheritance) |
| * <signal.h> support for `sigaction64_t` and `sigset64_t` allowing LP32 access to real-time signals |
| * <spawn.h> |
| * `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 <nl_types.h>) |
| * `ctermid` |
| * all 6 <grp.h>/<pwd.h> (get|set|end)(gr|pw)ent functions |
| * `futimes`/`futimesat`/`lutimes` |
| * `getdomainname`/`setdomainname` |
| * `getsubopt` |
| * `hasmntopt` |
| * `mallopt` |
| * `mblen` |
| * 4 <sys/msg.h> `msg*` functions |
| * <langinfo.h> `nl_langinfo`/`nl_langinfo_l` |
| * `pthread_getname_np` |
| * 2 new Linux system calls `quotactl` and `sync_file_range` |
| * 4 <sys/sem.h> `sem*` functions |
| * 4 <sys/shm.h> `shm*` functions |
| * 5 legacy <signal.h> functions: `sighold`/`sigignore`/`sigpause`/`sigrelse`/`sigset` |
| * `strtod_l`/`strtof_l`/`strtol_l`/`strtoul_l` |
| * <wctype.h> `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. |
