Re: building GNU gettext on AIX

[Bruno Haible]

David Edelsohn wrote:
> >     ibm-clang links against libpthread.a as well:
> >     $ ldd /opt/IBM/openxlC/17.1.1/bin/.ibm-clang.orig
> >     /opt/IBM/openxlC/17.1.1/bin/.ibm-clang.orig needs:
> >          /usr/lib/libpthreads.a(shr_xpg5_64.o)
> >          /usr/opt/zlibNX/lib/libz.a(libz.so.1)
> >          /usr/lib/libcurses.a(shr42_64.o)
> >          /usr/lib/libiconv.a(shr4_64.o)
> >          /usr/lib/libc++.a(shr_64.o)
> >          /usr/lib/libc++abi.a(libc++abi.so.1)
> >          /usr/lib/libc.a(shr_64.o)
> >          /usr/lib/libpthreads.a(_shr_xpg5_64.o)
> >          /usr/lib/libc++.a(libc++.so.1)
> >          /usr/lib/libunwind.a(libunwind.so.1)
> >          /usr/lib/libc.a(_shr_64.o)
> >          /unix
> >          /usr/lib/libcrypt.a(shr_64.o)
> >
> 
> I have asked the IBM Clang team why ibm-clang depends on libpthreads.

The reason is that
  - For a library, it is a normal expectation nowadays that it is
    multithread-safe.
  - Making a library multithread-safe (without major hacks) means to do
    locking or to call pthread_once / call_once in some places.
  - The ISO C 11 threading functions in libc have some drawbacks compared
    to the pthread functions. [1] So most developer prefer to rely on the
    POSIX threads API.
  - Since AIX does not have the POSIX mutex functions in libc and does not
    support weak symbols like in ELF, this means a dependency to
    pthread_mutex_lock or pthread_once.
  - Accordingly, in the list of libraries above, 3 libraries need pthread*
    symbols:

$ nm -X 64 /usr/lib/libc++abi.a | grep ' U ' | grep pthread_mutex
pthread_mutex_lock   U           -
pthread_mutex_unlock U           -
$ nm -X 64 /usr/lib/libc++.a | grep ' U ' | grep pthread_mutex
pthread_mutex_destroy U           -
pthread_mutex_init   U           -
pthread_mutex_lock   U           -
pthread_mutex_trylock U           -
pthread_mutex_unlock U           -
pthread_mutexattr_destroy U           -
pthread_mutexattr_init U           -
pthread_mutexattr_settype U           -
$ nm -X 64 /usr/opt/zlibNX/lib/libz.a | grep ' U ' | grep pthread_mutex
pthread_mutex_destroy U           -
pthread_mutex_init   U           -
pthread_mutex_lock   U           -
pthread_mutex_unlock U           -

Bruno

[1] Lock initialization is clumsy. The return value of a thread is only an
    'int', not a pointer. Etc.