libc-query

Compile-time detection of libc symbol and header availability for Zig cross-compilation targets.

Covers glibc, musl, macOS, FreeBSD, OpenBSD, NetBSD, DragonFly, Windows (mingw64), and WASI (preview 1 and preview 2).

What is tracked

libc_features — optional libc functions: accept4, alarm, arc4random, arc4random_buf, arc4random_uniform, asprintf, backtrace_symbols, clock_gettime, copy_file_range, copyfile, elf_aux_info, eventfd, explicit_bzero, fcntl, fdatasync, fnmatch, freeaddrinfo, freezero, fseeko, fsetxattr, ftruncate, getaddrinfo, getaddrinfo_threadsafe, getauxval, getdelim, getentropy, geteuid, gethostbyname_r, gethostname, getifaddrs, getline, getopt, getpagesize, getpass_r, getpeereid, getpeername, getppid, getprogname, getpwuid, getpwuid_r, getrandom, getrlimit, getsockname, gmtime_r, if_nametoindex, inet_aton, inet_ntop, inet_pton, localtime_r, localeconv_l, mbstowcs_l, memmem, memrchr, memset_s, mkdtemp, pipe, pipe2, poll, posix_fadvise, posix_fallocate, ppoll, preadv, pwritev, readpassphrase, reallocarray, recallocarray, sched_yield, sendmmsg, sendmsg, setmode, setproctitle, setrlimit, sigaction, siginterrupt, sigsetjmp, signal, socket, socketpair, strcasecmp, strchrnul, strerror_r, strlcat, strlcpy, strncasecmp, strndup, strnlen, strsep, strsignal, strtonum, sync_file_range, syncfs, syslog, timingsafe_bcmp, timingsafe_memcmp, uselocale, utimes, vasprintf, wcstombs_l.

libc_headers — system headers: headers always present on all supported targets (e.g. stdlib.h, string.h, fcntl.h) plus OS-specific ones such as sys/epoll.h, sys/event.h, sys/ucred.h, netinet/tcp.h, sys/ioctl.h, sys/resource.h, linux/tcp.h (Linux only), crtdefs.h (Windows only), and others.

libc_types — struct field and typedef presence: sa_family_t, socklen_t, suseconds_t (all POSIX targets including WASI), struct_sockaddr_sa_len (BSDs and macOS), struct_tm_tm_zone (all POSIX targets except WASI, which uses __tm_zone).

libc_constants — constant/declaration availability: clock_monotonic (all POSIX targets including WASI), clock_monotonic_raw (Linux and Darwin), f_fullfsync (macOS only), msg_nosignal (Linux, BSDs, DragonFly, macOS 14.0+), o_nonblock (all POSIX targets including WASI).

For glibc, function availability is per-architecture and derived from Zig’s bundled abilists file.

Usage

Add this repo as a dependency to your build.zig.zon:

zig fetch --save git+https://github.com/agagniere/libc-query

Then in your build.zig:

const libcquery = @import("libcquery");

// Then, in your build function:

const features   = libcquery.libc_features.detect(target.result);
const headers    = libcquery.libc_headers.detect(target.result);
const types      = libcquery.libc_types.detect(target.result);
const constants  = libcquery.libc_constants.detect(target.result);

if (features.strlcpy)                  { ... }
if (headers.sys_epoll_h)               { ... }
if (types.struct_sockaddr_sa_len)      { ... }
if (constants.f_fullfsync)             { ... }

Each detect() takes a std.Target and returns a struct of bool fields. Fields default to false for unknown targets (except POSIX-ubiquitous ones which default to true).

Regenerating generated files

glibc_abi.zig and libc_headers.zig are generated from Zig’s bundled libc data:

python3 generate_glibc_abi.py | zig fmt --stdin > glibc_abi.zig
python3 generate_libc_headers.py | zig fmt --stdin > libc_headers.zig

Requires zig on PATH. Run after upgrading the Zig toolchain.