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>
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 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)sigaction64_t
and sigset64_t
allowing LP32 access to real-time signalsswab
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
bsd_signal
catclose
/catgets
/catopen
(adding <nl_types.h>)ctermid
futimes
/futimesat
/lutimes
getdomainname
/setdomainname
getsubopt
hasmntopt
mallopt
mblen
msg*
functionsnl_langinfo
/nl_langinfo_l
pthread_getname_np
quotactl
and sync_file_range
sem*
functionsshm*
functionssighold
/sigignore
/sigpause
/sigrelse
/sigset
strtod_l
/strtof_l
/strtol_l
/strtoul_l
towctrans
/towctrans_l
/wctrans
/wctrans_l
New libc functions in N:
fread
/fwrite
/getcwd
/pwrite
/write
)_FILE_OFFSET_BITS=64
functions, completing _FILE_OFFSET_BITS=64
support in bionic (8)pthread_barrier*
functionspthread_spin*
functionslockf
/preadv
/pwritev
/scandirat
and off64_t
variantsadjtimex
/clock_adjtime
getifaddrs
/freeifaddrs
/if_freenameindex
/if_nameindex
getgrgid_r
/getgrnam_r
fileno_unlocked
/strchrnul
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
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
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 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.
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.