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 (pthread_cancel).
* 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.
Current libc symbols: https://android.googlesource.com/platform/bionic/+/master/libc/libc.map.txt
New libc functions in Q (API level 29):
* timespec_get (C11 <time.h> addition)
* reallocarray (BSD/GNU extension in <malloc.h> and <stdlib.h>)
* res_randomid (in <resolv.h>)
* pthread_sigqueue (GNU extension)
* getloadavg (BSD/GNU extension in <stdlib.h>)
New libc behavior in Q (API level 29):
* Whole printf family now supports the GNU %m extension, rather than a
special-case hack in syslog.
* popen now always uses O_CLOEXEC, not just with the e extension.
* Bug fixes to handling of UTF-8 U+fffe/U+ffff and code points above U+10ffff.
* aligned_alloc correctly verifies that size is a multiple of alignment.
* Using %n with the printf family is now reported as a FORTIFY failure.
Previous versions of Android would ignore the %n but not consume the
corresponding pointer argument, leading to obscure errors. The scanf family
is unchanged.
* Support in strptime for %F, %G, %g, %P, %u, %V, and %v.
(strftime already supported them all.)
* fdsan detects common file descriptor errors at runtime.
New libc functions in P (API level 28):
* aligned_alloc
* __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 (API level 28):
* %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).
* Using a pthread_mutex_t after it's been destroyed will be detected at
runtime and reported as a FORTIFY failure.
* Passing a null FILE* or DIR* to libc is now detected at runtime and
reported as a FORTIFY failure.
New libc functions in O (API level 26):
* 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 behavior in O (API level 26):
* Passing an invalid pthread_t to libc is now detected at runtime and
reported as a FORTIFY failure. Most commonly this is a result of confusing
pthread_t and pid_t.
New libc functions in N (API level 24):
* 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
* <ifaddrs.h> getifaddrs/freeifaddrs/if_freenameindex/if_nameindex
* getgrgid_r/getgrnam_r
* GNU extensions fileno_unlocked/strchrnul
* 32-bit prlimit
New libc behavior in N (API level 24):
* sem_wait now returns EINTR when interrupted by a signal.
New libc functions in M (API level 23):
* <dirent.h> telldir, seekdir.
* <malloc.h> malloc_info.
* <netdb.h> gethostbyaddr_r, gethostbyname2_r.
* <pthread.h> pthread_rwlockattr_getkind_np/pthread_rwlockattr_setkind_np.
* <pty.h> forkpty, openpty.
* <signal.h> sigqueue, sigtimedwait, sigwaitinfo.
* <stdio.h> fmemopen, open_memstream, feof_unlocked, ferror_unlocked, clearerr_unlocked.
* <stdio_ext.h> __flbf, __freadable, __fsetlocking, __fwritable, __fbufsize, __fpending, _flushlbf, __fpurge.
* <stdlib.h> mkostemp/mkostemps, lcong48.
* <string.h> basename, strerror_l, strerror_r, mempcpy.
* <sys/sysinfo.h> get_nprocs_conf/get_nprocs, get_phys_pages, get_avphys_pages.
* <sys/uio.h> process_vm_readv/process_vm_writev.
* clock_getcpuclockid, login_tty, mkfifoat, posix_madvise, sethostname, strcasecmp_l/strncasecmp_l.
* <wchar.h> open_wmemstream, wcscasecmp_l/wcsncasecmp_l, wmempcpy.
* all of <error.h>.
* 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.
New libc functions in L (API level 21):
* <android/dlext.h>.
* <android/set_abort_message.h>.
* <arpa/inet.h> inet_lnaof, inet_netof, inet_network, inet_makeaddr.
* <wctype.h> iswblank.
* <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.
* <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>.
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
Current libm symbols: https://android.googlesource.com/platform/bionic/+/master/libm/libm.map.txt
0 remaining missing POSIX libm functions.
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.
libm function count over time:
G 158, J-MR2 164, L 220, M 265, O 284
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.
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 invalidpthread_t is handled. For pthread_detach, pthread_getcpuclockid,pthread_getschedparam/pthread_setschedparam, pthread_join, andpthread_kill, instead of returning ESRCH when passed an invalidpthread_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 topthread_attr_setdetachstate instead, or usepthread_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.
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.
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
(example)[https://source.android.com/devices/tech/debug/native-crash#fortify].
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
(FORTIFY in Android)[https://android-developers.googleblog.com/2017/04/fortify-in-android.html]
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.