Re: [Xenomai-core] [PATCH] blackfin: build xenomai in FLAT format

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

yi li wrote:
> On Wed, Feb 25, 2009 at 6:23 PM, Gilles Chanteperdrix
> <gilles.chanteperdrix@xenomai.org> wrote:
>> yi li wrote:
>>> On Wed, Feb 25, 2009 at 12:30 AM, Philippe Gerum <rpm@xenomai.org> wrote:
>>>>> 2.  libpthread_rt.la should not depend on "lpthread".
>>>>>
>>>> Nak. In flat mode, turning the link dependencies order upside down will not buy
>>>> us anything. Two-phase link is the only way to prevent circular/invalid
>>>> dependencies with a static only format when symbol wrapping is involved.
>>>>
>>> Agree. But "libpthread_rt_la_LDFLAGS" should not include "-lpthread",
>>> otherwise libtool will think libpthread_rt.a depends on libpthread.
>>> I don't think there is such a dependency, isn't it?
>> Look at libpthread_rt code.
>>
> 
> Here is the problem:
> 
> /bin/bash ../../../libtool --tag=CC   --mode=link bfin-uclinux-gcc
> -pipe -Wall -g -O2      -mcpu=bf527-0.1
> -Wl,@/home/adam/new_workspace/local_svn/kernel/adeos/uclinux-dist/user/xenomai/xenomai-2.4.x/src/skins/posix/posix.wrappers
> -D_GNU_SOURCE -D_REENTRANT -Wall -pipe -Wl,-elf2flt    -mcpu=bf527-0.1
> -o cyclictest cyclictest-cyclictest.o -lpthread -lrt
> ../../skins/posix/libpthread_rt.la
> mkdir .libs
> bfin-uclinux-gcc -pipe -Wall -g -O2 -mcpu=bf527-0.1
> -Wl,@/home/adam/new_workspace/local_svn/kernel/adeos/uclinux-dist/user/xenomai/xenomai-2.4.x/src/skins/posix/posix.wrappers
> -D_GNU_SOURCE -D_REENTRANT -Wall -pipe -Wl,-elf2flt -mcpu=bf527-0.1 -o
> cyclictest cyclictest-cyclictest.o  -lrt
> ../../skins/posix/.libs/libpthread_rt.a -lpthread
> /home/adam/workspace/toolchain/4.1-1220/bfin-uclinux/bin/../bfin-uclinux/runtime/usr/lib/libpthread.a(manager.o):
> In function `__pthread_manager':
> libpthread/linuxthreads.old/manager.c:173: undefined reference to
> `___wrap_select'
> /home/adam/workspace/toolchain/4.1-1220/bfin-uclinux/bin/../bfin-uclinux/runtime/usr/lib/libpthread.a(mutex.o):
> In function `__pthread_once_fork_child':
> libpthread/linuxthreads.old/mutex.c:357: undefined reference to
> `___wrap_pthread_cond_init'
> /home/adam/workspace/toolchain/4.1-1220/bfin-uclinux/bin/../bfin-uclinux/runtime/usr/lib/libpthread.a(mutex.o):
> In function `__pthread_once':
> libpthread/linuxthreads.old/mutex.c:308: undefined reference to
> `___wrap_pthread_cond_wait'
> libpthread/linuxthreads.old/mutex.c:325: undefined reference to
> `___wrap_pthread_cond_broadcast'
> /home/adam/workspace/toolchain/4.1-1220/bfin-uclinux/bin/../bfin-uclinux/runtime/usr/lib/libpthread.a(mutex.o):
> In function `pthread_once_cancelhandler':
> libpthread/linuxthreads.old/mutex.c:281: undefined reference to
> `___wrap_pthread_cond_broadcast'
> collect2: ld returned 1 exit status
> 
> In my opinion,  "-lpthread" does not need to be set in
> "libpthread_rt_la_LDFLAGS". The application (e.g, cyclictest) decides
> which libraries to link with.

-lpthread does need to be set in libpthread_rt_la_LDFLAGS, if you look
at libpthread_rt code (which you apparently do not want to dot), you
will see that it uses libpthread functions.

The issue you have has already been discussed on this list, and we
already know the correct workaround. The correct workaround is not to
link with -lpthread first. Linking with -lpthread first leads to broken
binaries, whose libpthread functions call libpthread_rt functions. The
correct workaround is to link your binary in two stages, or to forget
about FLAT and use FDPIC.

-- 
                                                 Gilles.