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crtl: the last declared-but-unimplemented functions

Why a missing body is worse than a missing declaration

Each of these is declared in a crtl header, so the C frontend's unresolved-extern fallback binds the call to libc.so.6. On a glibc host the program then produces correct output — and quietly stops being self-contained. clock_gettime was exactly this and was fixed 2026-08-05:

$ readelf -d prog | grep NEEDED
 0x0000000000000001 (NEEDED)  Shared library: [libc.so.6]

The values were right, the linkage was not. Assert the linkage, not just the output — that is what this probe is for.

The seven, with what each needs

function header note
atexit stdlib.h The awkward one — see below. Today it is a hard runtime link error (undefined symbol: atexit), so at least it is loud.
poll poll.h PalPoll exists but is per-handle (PalPoll(handle, events, timeoutMs)); real poll(fds[], nfds, timeout) needs an array-shaped PAL bridge, not a loop over the existing one (a loop cannot block on the set).
ioctl sys/ioctl.h DONE 2026-08-05. This row was WRONG: PalIoctl was already a fully general syscall(SYS_ioctl, fd, cmd, argp) — __pxx_isatty had been using it for the single TCGETS case all along. No new PAL entry was needed, only __pxx_ioctl exposing it and a crtl wrapper doing the -1/errno conversion. Measure before believing a scoping line. ESP: IDF routes to lwip_ioctl, bare answers PAL_ERR_UNSUPPORTED, which surfaces as -1/errno — a refusal, not a wrong answer.
chmod sys/stat.h DONE 2026-08-05. Goes through fchmodat(AT_FDCWD, …) — aarch64 and riscv have no legacy chmod syscall, same as symlink/link.
umask sys/stat.h DONE 2026-08-05. The one syscall here with no error path: it always succeeds and returns the previous mask, so no -1/errno conversion.
msync sys/mman.h DONE 2026-08-05. No-op success, matching munmap/mprotect in the same file — mmap there is a stub returning MAP_FAILED, so there is never a mapping to flush.
mremap sys/mman.h DONE 2026-08-05. Must return a POINTER, so it cannot pretend: fails like mmap does (MAP_FAILED + ENOMEM). Linux-specific and variadic; the optional 5th arg is not read.

chmod and umask were the cheapest and are done. Their syscall numbers were added to all five arch tables in platform_backend.pas and verified by running the probe on x86-64, i386, arm32 and aarch64 — a wrong number there is exactly how exit_group came to be fgetxattr on 32-bit ([[bug-a-explicit-int64-cast-of-nativeint-does-not-extend-on-32bit]]'s sibling, fixed the same night). riscv32 shares aarch64's asm-generic numbers and is not runnable here.

atexit cannot be finished inside crtl

crtl owns exit(), so registering handlers and running them there is easy. It does not own the other exit path: the C entry stub is call main; exit_group(retval), emitted by the compiler, and a plain return from main bypasses crtl entirely. So a crtl-only atexit would run handlers for exit() and silently skip them for return — which is worse than not having it, because it would look implemented.

There is already a mechanism to hook: __pxx_run_finalizers / EmitFinalizerRunnerBody (symtab.inc:5616, cparser.inc:8453), the shell every Pascal exit path calls. The C entry stub does not call it. Wiring it in — so both return from main and exit() run registered handlers, in LIFO order — is a Track C/A change; the crtl half (the handler table) is Track B and should land with it, not before.

Suggested split: file the stub change as a Track C ticket, then implement atexit here against it.

Gate

tools/crtl_decl_probe.sh reports 0 unimplemented; each new function byte-matches gcc in tools/gcc_diff_probe.sh; and a program calling it has no DT_NEEDED (readelf -d).