Linking to pthread library: undefined reference

[Frank Behrens]

Gergely CZUCZY <phoemix at harmless.hu> wrote on 15 Jun 2007 19:18:
> On Fri, Jun 15, 2007 at 07:01:19PM +0200, Frank Behrens wrote:
> > I try to link an milter (sendmail mail filter) test application and get an error I do not 
> > understand. I use FreeBSD 6.2-STABLE-200705211513 with an userland from May-03.
> > In my Makefile I have:
> > CFLAGS+=	-I/usr/local/include -std=c99 -pthread -v
> > LDADD+=		-L/usr/local/lib -lmilter
> > 
> > This gives linker command:
> > cc -O2 -pipe -fno-strict-aliasing -march=pentium4 -I/usr/local/include -std=c99 -pthread -v -g -
> > DDEBUG=1 -O1 -fno-omit-frame-pointer -Wsystem-headers -Wall -Wno-format-y2k -W -
> > Wno-unused-parameter -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wreturn-
> > type -Wcast-qual -Wwrite-strings -Wswitch -Wshadow -Wcast-align -Wunused-parameter -
> > Wchar-subscripts -Winline -Wnested-externs -Wredundant-decls  -o fmilter fmilter.o -
> > L/usr/local/lib -lmilter
> > Using built-in specs.
> > Configured with: FreeBSD/i386 system compiler
> > Thread model: posix
> > gcc version 3.4.6 [FreeBSD] 20060305
> >  /usr/bin/ld -V -dynamic-linker /libexec/ld-elf.so.1 -o fmilter /usr/lib/crt1.o /usr/lib/crti.o 
> > /usr/lib/crtbegin.o -L/usr/local/lib -L/usr/lib fmilter.o -lmilter -lgcc -lpthread -lc -lgcc 
> I don't think this is the problem here, but you should link against -pthread, and
> not -lpthread. pthread is just an API here, while -pthread refers to the
> system-default threading library (with a pthread interface).

The -lpthread was added automatically, I used in CFLAGS -pthread only.

> > /usr/lib/crtend.o /usr/lib/crtn.o
> > GNU ld version 2.15 [FreeBSD] 2004-05-23
> >   Supported emulations:
> >    elf_i386_fbsd
> > /usr/lib/libmilter.so: undefined reference to `pthread_detach'
> > 
> > In my opinion the symbol should be found in
> > /usr/lib/libpthread.so@ -> /lib/libpthread.so.2
> > 
> > When I look into the libraries I see
> > > objdump -T /usr/lib/libmilter.so | fgrep detach
> > 00000000      D  *UND*  00000000 pthread_detach
> > 
> > > objdump -T /usr/lib/libpthread.so | fgrep pthread_detach
> > 000077d4  w   DF .text  000003a4  LIBTHREAD_1_0 pthread_detach
> > 000077d4 g    DF .text  000003a4  LIBTHREAD_1_0 _pthread_detach

What does LIBPTHREAD_1_0 mean? 

Regards,
   Frank
-- 
Frank Behrens, Osterwieck, Germany
PGP-key 0x5B7C47ED on public servers available.