Re: pkg/58249: SIGABRT misc/stellarium by "_res is not supported for multi-threaded programs" in libpthread

[Havard Eidnes <he%NetBSD.org@localhost>]

> _res is not supported for multi-threaded programs.
> Abort trap (core dumped)

Yep, this is a consequence of using the now-deprecated API to the
resolver in the c library in a threaded program, ref.
resolver(3), which among other things says:

     The functions res_init(), res_isourserver(), fp_nquery(), p_query(),
     hostalias(), res_query(), res_search(), res_querydomain(), res_mkquery(),
     res_send(), res_update(), res_close() are deprecated and are supplied for
     compatibility with old source code.  They use global configuration and
     state information that is kept in the structure _res rather than that
     referenced through statp.

It's no big surprise that a threaded program cannot work well
with the use of global state variables possibly tweaked
independently by different threads.

As for how and where to fix, that's another matter, though this
is perahps a hint:

> This shows call __res_state by libQt6Network.so ->
> libpthread.so, and libpthread say "_res is not supported for
> multi-threaded programs".

So somewhere deep in the bowels of Qt6?  And sure enough:

./src/network/kernel/qhostinfo_unix.cpp:            res_init();

Looking at the code, it may be as simple as just #if 0'ing out
the section, ref. the preceding comment which says

#if QT_CONFIG(libresolv)
    // OSes known or thought to reach here: AIX, NetBSD, Solaris,
    // Linux with MUSL (though res_init() does nothing and is unnecessary)

"does nothing and is unnecessary".

What about doing

#if 0
        if ((_res.options & RES_INIT) == 0)
            refresh = true;
#endif

and

#if 0
        if (refresh) {
            lastStat = st;
            res_init();
        }
#endif

That's in maybeRefreshResolver(), and it has exceptions for
Darwin, FreeBSD, OpenBSD and QNX, which all "auto-refresh" or in
the case of QNX, "res_init() is not thread-safe".  I'm not sure
if NetBSD "auto-refreshes" when /etc/resolv.conf is modified, but
looking at the code in libc's resolver library makes me think so,
ref. res_check() which is called from res_nsend().


But, no, that's not the only one:

    return domainNameFromRes(&_res);

but possibly that code is never executed on NetBSD (looking at
the previous section which does res_ninit() and tries to peel out
the domain name from that state.

Regards,

- Havard