1 # Android bionic status 2 3 ## Bionic function availability 4 5 ### POSIX 6 7 You can see the current status with respect to POSIX in the form of tests: 8 https://android.googlesource.com/platform/bionic/+/master/tests/headers/posix/ 9 10 Some POSIX functionality is not supported by the Linux kernel, and 11 is guarded with tests for `__linux__`. Other functionality is not 12 supported by bionic or glibc, and guarded with tests for `__BIONIC__` 13 and `__GLIBC__`. In other cases historical accidents mean 32-bit 14 bionic diverged but 64-bit bionic matches POSIX; these are guarded with 15 `__LP64__`. 16 17 Most bionic-only diversions should be accompanied by an explanatory comment. 18 19 Missing functions are either obsolete or explicitly disallowed by SELinux: 20 * `a64l`/`l64a` 21 * `confstr` 22 * `crypt`/`encrypt`/`setkey` 23 * `gethostid` 24 * `shm_open`/`shm_unlink` 25 * `sockatmark` 26 27 Missing functionality: 28 * `<aio.h>` 29 * `<wordexp.h>` 30 * Thread cancellation 31 * Robust mutexes 32 33 Run `./libc/tools/check-symbols-glibc.py` in bionic/ for the current 34 list of POSIX functions implemented by glibc but not by bionic. 35 36 ### libc 37 38 Current libc symbols: https://android.googlesource.com/platform/bionic/+/master/libc/libc.map.txt 39 40 New libc functions in P: 41 * `__freading`/`__fwriting` (completing <stdio_ext.h>) 42 * `endhostent`/`endnetent`/`endprotoent`/`getnetent`/`getprotoent`/`sethostent`/`setnetent`/`setprotoent` (completing <netdb.h>) 43 * `fexecve` 44 * `fflush_unlocked`/`fgetc_unlocked`/`fgets_unlocked`/`fputc_unlocked`/`fputs_unlocked`/`fread_unlocked`/`fwrite_unlocked` 45 * `getentropy`/`getrandom` (adding <sys/random.h>) 46 * `getlogin_r` 47 * `glob`/`globfree` (adding <glob.h>) 48 * `hcreate`/`hcreate_r`/`hdestroy`/`hdestroy_r`/`hsearch`/`hsearch_r` (completing <search.h>) 49 * `iconv`/`iconv_close`/`iconv_open` (adding <iconv.h>) 50 * `pthread_attr_getinheritsched`/`pthread_attr_setinheritsched`/`pthread_setschedprio` 51 * `pthread_mutexattr_getprotocol`/`pthread_mutexattr_setprotocol` (mutex priority inheritance) 52 * <signal.h> support for `sigaction64_t` and `sigset64_t` allowing LP32 access to real-time signals 53 * <spawn.h> 54 * `swab` 55 * `syncfs` 56 57 New libc behavior in P: 58 * `%C` and `%S` support in the printf family (previously only the wprintf family supported these) 59 * `%mc`/`%ms`/`%m[` support in the scanf family 60 * `%s` support in strptime (strftime already supported it) 61 62 New libc functions in O: 63 * `sendto` FORTIFY support 64 * `__system_property_read_callback`/`__system_property_wait` 65 * legacy `bsd_signal` 66 * `catclose`/`catgets`/`catopen` (adding <nl_types.h>) 67 * `ctermid` 68 * all 6 <grp.h>/<pwd.h> (get|set|end)(gr|pw)ent functions 69 * `futimes`/`futimesat`/`lutimes` 70 * `getdomainname`/`setdomainname` 71 * `getsubopt` 72 * `hasmntopt` 73 * `mallopt` 74 * `mblen` 75 * 4 <sys/msg.h> `msg*` functions 76 * <langinfo.h> `nl_langinfo`/`nl_langinfo_l` 77 * `pthread_getname_np` 78 * 2 new Linux system calls `quotactl` and `sync_file_range` 79 * 4 <sys/sem.h> `sem*` functions 80 * 4 <sys/shm.h> `shm*` functions 81 * 5 legacy <signal.h> functions: `sighold`/`sigignore`/`sigpause`/`sigrelse`/`sigset` 82 * `strtod_l`/`strtof_l`/`strtol_l`/`strtoul_l` 83 * <wctype.h> `towctrans`/`towctrans_l`/`wctrans`/`wctrans_l` 84 85 New libc functions in N: 86 * more FORTIFY support functions (`fread`/`fwrite`/`getcwd`/`pwrite`/`write`) 87 * all remaining `_FILE_OFFSET_BITS=64` functions, completing `_FILE_OFFSET_BITS=64` support in bionic (8) 88 * all 7 `pthread_barrier*` functions 89 * all 5 `pthread_spin*` functions 90 * `lockf`/`preadv`/`pwritev`/`scandirat` and `off64_t` variants 91 * `adjtimex`/`clock_adjtime` 92 * `getifaddrs`/`freeifaddrs`/`if_freenameindex`/`if_nameindex` 93 * `getgrgid_r`/`getgrnam_r` 94 * GNU extensions `fileno_unlocked`/`strchrnul` 95 * 32-bit `prlimit` 96 97 libc function count over time: 98 G 803, H 825, I 826, J 846, J-MR1 873, J-MR2 881, K 896, L 1116, M 1181, N 1226, O 1278 99 100 ``` 101 ndk-r17$ for i in `ls -1v platforms/android-*/arch-arm/usr/lib/libc.so` ; do \ 102 echo $i; nm $i | grep -vw [AbdNnt] | grep -vw B | wc -l ; done 103 ``` 104 105 ### libm 106 107 Current libm symbols: https://android.googlesource.com/platform/bionic/+/master/libm/libm.map.txt 108 109 0 remaining missing POSIX libm functions. 110 111 19 new libm functions in O: complex trig/exp/log functions. 112 113 libm function count over time: 114 G 158, J-MR2 164, L 220, M 265, O 284 115 116 117 118 ## Target API level behavioral differences 119 120 Most bionic bug fixes and improvements have been made without checks for 121 the app's `targetSdkVersion`. As of O there were exactly two exceptions, 122 but there are likely to be more in future because of Project Treble. 123 124 ### Invalid `pthread_t` handling (targetSdkVersion >= O) 125 126 As part of a long-term goal to remove the global thread list, 127 and in an attempt to flush out racy code, we changed how an invalid 128 `pthread_t` is handled. For `pthread_detach`, `pthread_getcpuclockid`, 129 `pthread_getschedparam`/`pthread_setschedparam`, `pthread_join`, and 130 `pthread_kill`, instead of returning ESRCH when passed an invalid 131 `pthread_t`, if you're targeting O or above, they'll abort with the 132 message "attempt to use invalid pthread\_t". 133 134 Note that this doesn't change behavior as much as you might think: the 135 old lookup only held the global thread list lock for the duration of 136 the lookup, so there was still a race between that and the dereference 137 in the caller, given that callers actually need the tid to pass to some 138 syscall or other, and sometimes update fields in the `pthread_internal_t` 139 struct too. 140 141 We can't check a thread's tid against 0 to see whether a `pthread_t` 142 is still valid because a dead thread gets its thread struct unmapped 143 along with its stack, so the dereference isn't safe. 144 145 To fix your code, taking the affected functions one by one: 146 147 * `pthread_getcpuclockid` and `pthread_getschedparam`/`pthread_setschedparam` 148 should be fine. Unsafe calls to those seem highly unlikely. 149 150 * Unsafe `pthread_detach` callers probably want to switch to 151 `pthread_attr_setdetachstate` instead, or use 152 `pthread_detach(pthread_self());` from the new thread's start routine 153 rather than calling detach in the parent. 154 155 * `pthread_join` calls should be safe anyway, because a joinable thread 156 won't actually exit and unmap until it's joined. If you're joining an 157 unjoinable thread, the fix is to stop marking it detached. If you're 158 joining an already-joined thread, you need to rethink your design! 159 160 * Unsafe `pthread_kill` calls aren't portably fixable. (And are obviously 161 inherently non-portable as-is.) The best alternative on Android is to 162 use `pthread_gettid_np` at some point that you know the thread to be 163 alive, and then call `kill`/`tgkill` with signal 0 (which checks 164 whether a process exists rather than actually sending a 165 signal). That's still not completely safe because if you're too late 166 the tid may have been reused, but your code is inherently unsafe without 167 a redesign anyway. 168 169 ### Interruptable `sem_wait` (targetSdkVersion >= N) 170 171 POSIX says that `sem_wait` can be interrupted by delivery of a 172 signal. This wasn't historically true in Android, and when we fixed this 173 bug we found that existing code relied on the old behavior. To preserve 174 compatibility, `sem_wait` can only return EINTR on Android if the app 175 targets N or later. 176
