Commit f795d54591 ("libc,shared: detect newer library symbols at
runtime") replaced the build-time HAVE_EPOLL_PWAIT2 gate with a runtime
shim that resolves the libc symbol via dlsym(RTLD_DEFAULT, "epoll_pwait2").
That breaks on 32-bit architectures built with _TIME_BITS=64 (e.g. Debian
armhf since the time64 transition).
When _TIME_BITS=64 is in effect on a 32-bit target, glibc's <sys/epoll.h>
asm-renames the C identifier `epoll_pwait2` to the matching 64-bit-time_t
ABI symbol `__epoll_pwait2_time64`, so a normal C call resolves to the
variant whose `struct timespec` layout (16 bytes: s64 tv_sec, long tv_nsec,
long pad) matches what the compiler is using:
/* /usr/include/sys/epoll.h */
#ifndef __USE_TIME64_REDIRECTS
extern int epoll_pwait2 (int __epfd, struct epoll_event *__events,
int __maxevents,
const struct timespec *__timeout,
const __sigset_t *__ss) ...;
#else
# ifdef __REDIRECT
extern int __REDIRECT (epoll_pwait2, (int __epfd, ...,
const struct timespec *__timeout,
const __sigset_t *__ss),
__epoll_pwait2_time64) ...;
# else
# define epoll_pwait2 __epoll_pwait2_time64
# endif
#endif
dlsym() doesn't see that header-level rename and returns the legacy
32-bit-time_t `epoll_pwait2` symbol, which interprets only the first 8
bytes of the 16-byte timespec we hand it. With a little-endian layout
that means the legacy callee reads tv_sec = (low 32 bits of real tv_sec)
and tv_nsec = (high 32 bits of real tv_sec, normally 0). Sub-second
timeouts therefore become {0,0} and return immediately, while multi-
second timeouts get truncated to whole seconds.
That matches the test failure reported on armv7:
/* test_simple_timeout */
src/libsystemd/sd-event/test-event.c:724: Assertion failed:
Expected "t >= usec_add(f, some_time)",
but 571153514285 < 571154403965
(the 889680 us shortfall is consistent with a sub-second `some_time` that
got rounded down to zero by the truncated wait).
Fix it by adding a DEFINE_LIBC_ERRNO_SHIM_NAMED() variant of the macro
that takes an explicit dlsym symbol name string. Both macros keep their
own copy of the body so every `func` reference stays behind `#` or `##`,
otherwise the override-header `#define epoll_pwait2 epoll_pwait2_shim`
would rewrite the token before the inner macro could paste it (yielding
`epoll_pwait2_shim_shim`). src/libc/epoll.c then picks
"__epoll_pwait2_time64" under __USE_TIME_BITS64 so the cached function
pointer matches the timespec ABI the rest of the code is built with.
Follow-up for f795d54591
Co-developed-by: Claude Opus 4.7 <noreply@anthropic.com>
Weak symbols still introduce a version requirement on a newer libc.
Resolve each libc symbol via dlsym(RTLD_DEFAULT) from a per-shim
constructor and cache the result in a file-scope static instead. This
avoids the version requirement, keeps the call path free of atomics
(constructors run single-threaded before main() and before any signal
handler can fire), and keeps dlsym() out of contexts where it is not
async-signal-safe.
For libc syscall wrappers (pidfd_open, fsopen, openat2, etc.) we previously
gated the calls behind build-time HAVE_* checks. Replace these with shim
functions in src/libc/ that fall back to the raw syscall at runtime when the
loaded glibc lacks the symbol. The infrastructure lives in src/libc/libc-shim.h:
DEFINE_SYSCALL_SHIM falls back to a direct syscall, DEFINE_LIBC_SHIM returns
ENOSYS (for posix_spawn-family helpers that have no corresponding syscall), and
DEFINE_LIBC_ERRNO_SHIM sets errno=ENOSYS and returns -1 (for read/write-style
helpers). The weak reference to the libc symbol is bound via __asm__(\"name\")
rename so the bare libc identifier never appears as a C token — this avoids
both #undef boilerplate against override-header redirects and the resulting
-Wredundant-decls warning. Drop the corresponding cc.has_function() loop from
meson.build.
For optional libraries (libcryptsetup, libdw, libarchive), drop the per-symbol
HAVE_* checks. Always declare the prototypes, suppressing the redundant-decl
warnings via DISABLE_WARNING_REDUNDANT_DECLS and NOLINT, and resolve the symbols
after the main dlopen via a new DLSYM_OPTIONAL() helper that only assigns on
success. libcryptsetup's crypt_set_keyring_to_link / crypt_token_set_external_path
and libarchive's *_is_set wrappers use fallback functions as their pointer
initializers (returning -ENOSYS and 0 respectively), so call sites can invoke
the symbol unconditionally and just check for -ENOSYS where the \"not supported\"
distinction matters.
The same shim treatment applies to pidfd_spawn / posix_spawnattr_setcgroup_np
(src/libc/spawn.c) and epoll_pwait2 (src/libc/epoll.c), with corresponding
override headers in src/include/override/spawn.h and
src/include/override/sys/epoll.h. posix_spawn_wrapper() in process-util.c and
epoll_wait_usec() in sd-event.c now detect ENOSYS in the return value instead
of checking the function pointer, falling back to plain posix_spawn() and
epoll_wait() respectively. coredump-config and coredump-submit get a
dlopen_dw_has_dwfl_set_sysroot() helper. The kexec arch gate now uses
defined(__NR_kexec_file_load) directly; pidfd.h uses __has_include_next() to
decide whether to pull in glibc's header.
This lets binaries built against newer glibc / libcryptsetup / libdw /
libarchive headers still load and run on older targets where these symbols are
absent.
libcrypt was no longer built by default since glibc-2.38, and it has been
completely removed since glibc-2.39.
Let's always use libxcrypt, unless when building with musl. As already
major distribution already have libxcrypt-4.4.x, hence let's also bump
the required minimum version to 4.4.0.
libxcrypt cannot be built with musl, hence the previous fallback logic
in libcrypt-util.c are moved to musl/crypt.c.
Note, libxcrypt-4.4.0 was released on 2018-11-20.
See also #38608.
musl's getopt_long() behaves something different in handling optional arguments:
```
$ journalctl _PID=1 _COMM=systemd --since 19:19:01 -n all --follow
Failed to add match 'all': Invalid argument
```
This introduces getopt_long_fix() that reorders the passed arguments to make
getopt_long() provided by musl works as what we expect.
Also, musl's getopt() always behaves POSIXLY_CORRECT mode, and stops parsing
arguments when a non-option string found. Let's always use getopt_long().
musl provides XSI compliant strerror_r(), and it is slightly different
from the one by glibc.
Let's introduce a tiny wrapper to convert XSI strerror_r() to GNU one.
The wrapper also patches musl's spurious catchall error message.
Then, move syscall definitions to the wrapper, and prototypes are moved
to relevant headers.
This also adds checks for add_key() and request_key(), as one day
glibc may be going to add some of them separatedly.
The check for fspick in meson.build is dropped, as it is currently
unused in our code.
This also moves
- basic/missing_bpf.h -> include/override/linux/bpf.h,
- basic/missing_keyctl.h -> include/override/linux/keyctl.h.
Luca Boccassi
Yu Watanabe
Daan De Meyer
Zbigniew Jędrzejewski-Szmek
Emil Renner BerthingandYu Watanabe