[Xcb] [Bug 98048] libpthread-stubs must NOT provide symbols which depend on actual implementation

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98048

--- Comment #18 from Emil Velikov <emil.l.velikov at gmail.com> ---
Just saw your IRC poke, barring the handles. For the future - myself xexaxo,
Rob robclark, and Ian idr.

$ nm -CD --defined-only /usr/lib/libpthread-2.24.so  | grep
pthread_mutexattr_settype
000000000000bc30 T __pthread_mutexattr_settype
000000000000bc30 T pthread_mutexattr_settype
[emil at arch-x1c3 mesa]$ nm -CD --defined-only /usr/lib/libc-2.24.so   | grep
pthread_mutexattr_settype | wc -l
0

Dropping the symbols will fix the "brokenness" since then the pthread-stubs
will expand to a plain .pc file (no DSO), thus only libc/libpthread will be
used.
In practise all Linux distros will end up like ^^ since glibc and musl have
provided the fa6db2f9c01~1 symbols for quite a few years. IIRC even latest
Solaris does so.

Thinking about the days, where libc did not provide the stubs and fa6db2f9c01
were not around - things were bound to break in an identical way. For example:

Foo uses the fa6db2f9c01~1 pthreads API and links against pthreads-stubs. Be
that directly or indirectly by/in one of its dependencies.

Foo uses the stubs and then dlopens libbar2. The latter links against
libpthread and the weak pthread-stubs symbols are overwritten.

At this point we'll get issues similar to the one described.


If we are to fix this:
 a) in foo - this means that one will need to link against full blown pthreads,
even though it does not want/need it. That is because foo cannot know if the
modules that it is going to use will pull pthreads, pthread-stubs or neither.
 b) in pthread-stubs - one will end up re-implementing most of glibc
libc<>libpthread heuristics.

So if anything I'd consider making things blindingly obvious that if runtime X
doesn't provide pthread-stubs behaviour things can break at any point. Thus
suggest a pthreads link for the very odd platform.


/me goes to add error messages for libdrm/mesa if $pkg-config --libs
pthread-stubs is non-null

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