On Sun, Oct 19, 2008 at 03:39:20PM +0000, Gregor Jasny wrote: > 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: > >[EMAIL PROTECTED]:~/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?
Glibc has stubs for many of the pthread functions, that do nothing when libpthread isn't loaded. This way, code has not runtime performance for using mutexes and locking when there is no thread used. If your library only uses the stuff that the libc has stubs for, then you don't want to force linking against libpthread, as it will bring a performance penalty for mono-threaded programs. -- ·O· Pierre Habouzit ··O [EMAIL PROTECTED] OOO http://www.madism.org
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