[posix] E: Tracking POSIX feature gaps opted out in configure.host for *-nanvix*

[esaurez]

Tracking: POSIX feature gaps opted out in configure.host for *-nanvix*

Summary

While shipping the .so-enablement work (esaurez#3, #4), we explicitly opted out of four POSIX feature families that newlib's libc/posix/ ships, plus enabled HAVE_OPENDIR to defer dirent-API responsibility to libposix. Each opt-out is a deliberate "Nanvix does not implement this yet" marker that needs a long-term plan. This issue is the umbrella tracker so the disabled features are visible.

The opt-outs are not bugs in newlib — they use newlib's own capability-macro idiom (cf. the RTEMS entry at configure.host:623). But each cflag corresponds to a real gap on the Nanvix side that should eventually be closed so the cflag can be removed.

Disabled by PR-3 + PR-4

Feature	newlib gate	What it provides	Why disabled today	Sub-issue
Signal masks	-D_NO_SIGPROCMASK	sigprocmask, sigfillset, sigemptyset, sigaddset, sigdelset, sigismember, sigsuspend	Nanvix has no kernel-side per-thread signal-mask plumbing yet. PR-3 added the cflag to unblock libc/search/hash_page.c.	(to be filed against nanvix/nanvix + libposix)
posix_spawn family	-D_NO_POSIX_SPAWN	posix_spawn, posix_spawnp, posix_spawnattr_*, posix_spawn_file_actions_*	Needs fork+execve+sigprocmask; Nanvix has none of those primitives yet.	(folded with sigprocmask for now)
popen / pclose	-D_NO_POPEN	popen, pclose	Needs fork+pipe+execve+/bin/sh.	(to be filed)
wordexp / wordfree	-D_NO_WORDEXP	wordexp, wordfree	Shells out to /bin/sh for word expansion.	(to be filed)

Plus the HAVE_* opt-in (PR-4)

Macro	What it silences in newlib	Why it's set
-DHAVE_OPENDIR	opendir.c, readdir.c, closedir.c, dirfd.c, scandir.c, seekdir.c, telldir.c, rewinddir.c, ftw.c, nftw.c	Nanvix provides opendir/readdir/... in libposix using a different struct dirent layout (d_ino+d_name, no d_reclen). Newlib's BSD-style versions would not compile against Nanvix's <sys/dirent.h>.

HAVE_OPENDIR is not itself a missing feature — the API exists, just in libposix instead of newlib. But two related items in the same gate are missing everywhere on Nanvix:

Symbol	Status on Nanvix	Notes
ftw / nftw	missing everywhere	Currently empty because HAVE_OPENDIR silences libc/posix/{ftw,nftw}.c. Tree-walk APIs. Pure C — could land in libposix without kernel work; the easy win in this list.

What "done" looks like

Every cflag listed above can eventually be removed from *-nanvix* in newlib/configure.host. That requires implementations on the Nanvix side (kernel or libposix). This umbrella issue stays open until the cflag list is empty.

Suggested sub-issue breakdown (to be filed against nanvix/nanvix and/or nanvix/libposix)

1. sigprocmask + sigaction + sigsuspend — kernel + libposix; biggest item, blocks most others. Local note: nanvix-todo/nanvix-newlib-implement-sigprocmask.md (also being filed).
2. posix_spawn family — libposix; depends on fork/execve which are larger items.
3. popen / pclose — libposix; depends on pipe + fork + execve + /bin/sh.
4. wordexp / wordfree — libposix; depends on /bin/sh for expansion OR a pure-C re-implementation.
5. ftw / nftw — libposix; pure-C, just walks opendir/readdir — easy win, no kernel dep.

References

• fix(libc): guard hash_page sigprocmask use behind _NO_SIGPROCMASK esaurez/newlib#3 — opt-out PR that introduced _NO_SIGPROCMASK and _NO_POSIX_SPAWN.
• feat(configure): enable posix_dir for *-nanvix* esaurez/newlib#4 — opt-out PR that introduced _NO_POPEN, _NO_WORDEXP, and HAVE_OPENDIR.
• Local investigation notes: nanvix-todo/nanvix-newlib-disabled-posix-features.md