dh_shlibdeps: bogus? warnings when linking against pthread

[Gregor Jasny <gjasny@web.de>]

Hi,

when I build the libv4l package [1] the following warning is emitted:
> dpkg-shlibdeps: warning: dependency on libpthread.so.0 could be avoided if "debian/libv4l-0/usr/lib/libv4l1.so.0 debian/libv4l-0/usr/lib/libv4l2.so.0" were not uselessly linked against it (they use none of its symbols).

But libv4l1 and libv4l2 are using the pthread_mutex_* funtions:
> gjasny@Rincewind:~/src/debian/exp/libv4l$ objdump -T debian/libv4l-0/usr/lib/libv4l1.so.0
>
> debian/libv4l-0/usr/lib/libv4l1.so.0:     file format elf64-x86-64
>
> DYNAMIC SYMBOL TABLE:
> ...
> 0000000000000000      DF *UND*  0000000000000751  GLIBC_2.2.5 pthread_mutex_lock
> 0000000000000000      DF *UND*  000000000000000a  GLIBC_2.2.5 pthread_mutex_unlock
> ...

The weird thing is that this symbol is defined in libc and also in 
libpthread:

> $ objdump -T /lib/libc.so.6 |grep mutex_lock
> 00000000000dae50 g    DF .text  0000000000000027  GLIBC_2.2.5 pthread_mutex_lock
> $ objdump -T /lib/libpthread.so.0 |grep mutex_lock
> 0000000000008490 g    DF .text  0000000000000751  GLIBC_2.2.5 pthread_mutex_lock
> 0000000000008490 g    DF .text  0000000000000751  GLIBC_2.2.5 __pthread_mutex_lock

Can anyone shed some light on this issue?

Thanks,
Gregor

PS: Please keep CC I'm not subscribed to debian-devel

[1] git://git.debian.org/git/collab-maint/libv4l.git