Modules

Symbols counts the public declarations in each sub-package. Treat a low count as "only the essentials are wired up"; the one remaining stub is described at the bottom.

Module	C header	Symbols
libc.math	<math.h>	124
libc.stdlib	<stdlib.h>	84
libc.float	<float.h>	30
libc.limits	<limits.h> the widths of the integer types, and what a process may have	24
libc.unistd	<unistd.h>	208
libc.file	<stdio.h> file operations	32
libc.ctype	<ctype.h>	30
libc.sys.socket	<sys/socket.h>	44
libc.sys.stat	<sys/stat.h>	36
libc.sys.times	<sys/times.h>	2
libc.time	<time.h>	39
libc.fenv	<fenv.h>	26
libc.sys.mman	<sys/mman.h>	15
libc.sys.sigqueue	<signal.h> a signal sent with a number, and the two waits	5
libc.sys.inotify	<sys/inotify.h> watching files for what happens	24
libc.sys.eventfd	<sys/eventfd.h> a counter behind a descriptor	6
libc.aio	<aio.h> I/O handed over rather than waited for	24
libc.sys.sysinfo	<sys/sysinfo.h>	18
libc.sys.timer	<time.h> the timers Darwin does not have	12
libc.pthread	<pthread.h>	103
libc.threads	<threads.h> Linux only, the C11 threads	39
libc.string	<string.h>	48
libc.stdio	<stdio.h> output, buffering, pipes	43
libc.complex	<complex.h>	46
libc.sched	<sched.h>	15
libc.signal	<signal.h> an action, and a handler as its number	67
libc.spawn	<spawn.h> start a process without fork	25
libc.locale	<locale.h>	23
libc.sys.epoll	<sys/epoll.h>	7
libc.search	<search.h>	9
libc.dirent	<dirent.h>	22
libc.sys.wait	<sys/wait.h>	25
libc.inttypes	<inttypes.h>	7
libc.sys.resource	<sys/resource.h>	15
libc.network	<arpa/inet.h> byte order and address conversion	16
libc.netdb	<netdb.h> name and service lookup	66
libc.netif	<net/if.h> interface names and numbers	9
libc.regex	<regex.h> POSIX regular expressions	29
libc.glob	<glob.h> pathname matching	23
libc.grp	<grp.h> the group database	12
libc.iconv	<iconv.h> character encoding conversion	4
libc.ifaddrs	<ifaddrs.h> network interfaces	16
libc.langinfo	<langinfo.h> strings the locale decides	64
libc.fnmatch	<fnmatch.h> matching a single name	7
libc.libgen	<libgen.h> cutting a path in two	2
libc.logging	<syslog.h>	6
libc.pty	<pty.h> a terminal a program can hold	4
libc.fcntl	<fcntl.h>	49
libc.getopt	<getopt.h> taking a command line apart	12
libc.dlfcn	<dlfcn.h>	9
libc.wchar	<wchar.h>	99
libc.wordexp	<wordexp.h> shell-style word splitting	6
libc.wctype	<wctype.h>	5
libc.uchar	<uchar.h> the UTF-16 and UTF-32 conversions	4
libc.sys.statvfs	<sys/statvfs.h>	15
libc.sys.select	<sys/select.h>	9
libc.sys.shm	<sys/shm.h> shared memory	7
libc.sys.sem	<sys/sem.h> counters that wait	6
libc.poll	<poll.h>	14
libc.setjmp	<setjmp.h>	2
libc.execinfo	<execinfo.h> the stack the process is on	3
libc.sys.utsname	<sys/utsname.h>	8
libc.sys.sendfile	<sys/sendfile.h>	1
libc.sys.random	<sys/random.h>	3
libc.sys.prctl	<sys/prctl.h>	19
libc.sys.auxv	<sys/auxv.h>	3
libc.errno	<errno.h>	6
libc.pwd	<pwd.h>	18
libc.termios	<termios.h> how a terminal line is set	57
libc.tcp	<netinet/tcp.h> the options a connection keeps	4
libc.sys.un	<sys/un.h> an address that is a path	4
libc.sys.ipc	<sys/ipc.h> keys for System V objects	9
libc.sys.msg	<sys/msg.h> message queues	6
libc.utmpx	<utmpx.h> who is logged in, and where	29
libc.constant	C type aliases and constants	—
libc.utils	String/pointer helpers	—

Not started yet

libc.threads (<threads.h>) is Linux only: Apple never shipped C11 threads, and no Darwin SDK has the header. A header that one platform does not have has never disqualified a module here — libc.sys.epoll, libc.uchar and others are Linux-only on purpose, and say so — and this one is the same kind of thing, so importing it on Darwin will not link.

It is also the module that waited longest, and the reason was one argument: thrd_create takes a function pointer, and for most of this package's life nothing here could hand C one. That reading was wrong — a def that captures nothing converts to a thin function value, which is a code address, and thrd_create takes it where C takes its thrd_start_t — and once it was wrong, the whole module came with it: all twenty-five functions, including call_once and the thread-local destructor, are bound on the same discovery. tests/test_threads.mojo starts threads, hands a mutex and a condition variable to two of them at once, and proves a wake that cannot be lost.

What libc.pthread owns and libc.threads does not is everything POSIX added on top: attributes, cancellation, process-shared mutexes, barriers once the other side has them. threads.h is the smaller vocabulary, and a program that wants C11 spellings — or wants to read C11 code — gets it here over the same libcs.

One call this page used to name alongside the missing module was never behind that wall: atexit has no symbol in glibc, which exports __cxa_atexit and on_exit in its place, so on this platform there is nothing for a binding to link against whatever the callback situation is.

libc.math has no long double variants — no fabsl, no nexttoward — because Mojo has no type to pass: on x86-64 the C type is the 80-bit x87 format. libc.locale has no FE_DFL_ENV, see fenv_t.

libc.sys.epoll, libc.sys.prctl, libc.sys.sendfile, libc.sys.eventfd, libc.sys.inotify, libc.sys.sigqueue, libc.sys.timer, libc.sys.auxv, libc.threads and libc.uchar wrap Linux-only calls; importing them on Darwin will not link. libc.uchar is there because Darwin has no <uchar.h> — not in the 10.15 SDK, not in 14.4, and not in Apple's Libc sources — rather than because one call is missing from it. libc.sys.random holds one of each: getentropy, which both platforms have, and getrandom, which answers -1 on Darwin rather than going missing.

libc.stdio covers the <stdio.h> entry points that libc.file does not already own; see the note at the top of src/libc/stdio/syscalls.mojo. libc.complex models double complex and float complex as the two-field structs the ABI actually passes; long double complex is left out because Mojo has no 80-bit type.

What the suite does not ask

Three bindings are not asked anything, and every one of them has a reason that is about the call rather than about the suite:

• ioctl is variadic, and its third argument is the address that nearly every request writes its answer through. external_call emits a call whose arguments are all in registers, and arm64 hands a variadic callee its anonymous arguments on the stack instead: what the callee reads is a slot nobody wrote. FIONREAD through this binding answers 0 on Apple silicon and leaves the integer it was asked about untouched. It is the same wall that makes the call that opens a file here be openat rather than open.
• putwchar writes to a stream the whole process shares, and orients it: forking a child does not get a fresh stream to try it on, only the one the suite has already written to as bytes.
• pthread_atfork registers a fork handler that the just-in-time run this suite uses cannot resolve; a built binary links and answers fine.

None of them is known to be broken; they are simply not asked.

1058 bindings are asked something, and the 3 that are not have a reason each. Both numbers are read back out of this page by scripts/check-tests.py, and so is every call named above: the page fails the run as soon as it says a call is not asked and a test starts asking it.