Undefined reference to `clock_gettime`, although` -lrt` is specified

Question

I gave -lrt as the last linker flag to the compiler. But still get this error.

 arif@khost :~/sak/sak.exosip$ gcc eXo_init.c -I/opt/osip2/include -I/opt/exosip/include -L/opt/osip2/lib -L/opt/exosip/lib -leXosip2 -losipparser2 -losip2 -lrt /opt/osip2/lib/libosip2.so: undefined reference to `clock_gettime' collect2: ld returned 1 exit status 

The manual page says:

 NAME clock_getres, clock_gettime, clock_settime - clock and time functions SYNOPSIS #include <time.h> int clock_getres(clockid_t clk_id, struct timespec *res); int clock_gettime(clockid_t clk_id, struct timespec *tp); int clock_settime(clockid_t clk_id, const struct timespec *tp); Link with -lrt. 

So, I'm a little confused when I do it wrong.

I tried reading the characters in librt.so with no luck:

 arif@khost :~/sak/ortp/src/tests$ nm /lib/x86_64-linux-gnu/librt-2.15.so nm: /lib/x86_64-linux-gnu/librt-2.15.so: no symbols 

UPDATE 1 The reason I can not read characters from librt.so is because they are "separated". Where can I get character names?

 arif@khost :~/sak/ortp/src/tests$ file /lib/x86_64-linux-gnu/librt-2.15.so /lib/x86_64-linux-gnu/librt-2.15.so: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), BuildID[sha1]=0x375b2c35c4e6503a5d1a88ab6f76f5b6e0ee81df, for GNU/Linux 2.6.24, stripped 

UPDATE 2

Well, things get very confusing because the following test code compiles and works very well:

 #include <time.h> #include <unistd.h> #include <stdio.h> int main(int argc, char **argv, char **arge) { struct timespec tps, tpe; if ((clock_gettime(CLOCK_REALTIME, &tps) != 0) || (clock_gettime(CLOCK_REALTIME, &tpe) != 0)) { perror("clock_gettime"); return -1; } printf("%lu s, %lu ns\n", tpe.tv_sec-tps.tv_sec,tpe.tv_nsec-tps.tv_nsec); return 0; } 

Built with

 arif@khost :~/sak/sak.exosip$ gcc what.c -lrt 

UPDATE3 The code I'm trying to execute is:

 #include <eXosip2/eXosip.h> #include <netinet/in.h> #include <unistd.h> int ex_init(int port) { struct eXosip_t *eXcontext; int i; TRACE_INITIALIZE(6, stdout); i = eXosip_init(eXcontext); if (i != 0) return -1; i = eXosip_listen_addr(eXcontext, IPPROTO_UDP, NULL, port, AF_INET, 0); if (i != 0) { eXosip_quit(eXcontext); fprintf (stderr, "could not initialize transport layer\n"); return -1; } return 1; } int main(int argc, char **argv) { if(ex_init(1000)) printf("success \n"); return 0; } 

Answer 1

Well, the problem is resolved. If I pass this linker flag

 -Wl,--no-as-needed 

Before the list of libraries on the command line.

Why does this work, because on my platform the linker is always passed with -Wl,--as-needed .

From the ld manual:

 --as-needed --no-as-needed This option affects ELF DT_NEEDED tags for dynamic libraries mentioned on the command line after the --as-needed option. Normally the linker will add a DT_NEEDED tag for each dynamic library mentioned on the command line, regardless of whether the library is actually needed or not. --as-needed causes a DT_NEEDED tag to only be emitted for a library that satisfies an undefined symbol reference from a regular object file or, if the library is not found in the DT_NEEDED lists of other libraries linked up to that point, an undefined symbol reference from another dynamic library. --no-as-needed restores the default behaviour. 

Therefore, when --as-needed provided in front of the library, liker only links to the libraries listed in the NEEDED section of the library.

For example,

 -Wl,--as-needed -llibA -llibB -llibC 

Here - necessary - before libA . Therefore, during linking, the linker will consider the NEEDED libA section. If NEEDED libA listed in the NEEDED libA libC , then libB will not be bound.

This particular problem has arisen because

 arif@khost :~/sak/sak.exosip$ objdump -p /opt/osip2/lib/libosip2.so.10 | grep NEEDED NEEDED libosipparser2.so.10 NEEDED libc.so.6 

libosip2 does not list librt as NEEDED .

If I pass --no-as-needed , then all the libraries will be linked regardless of what is indicated in the ELF NEEDED section.

Although this should not be so, because

 arif@khost :~/sak/sak.exosip$ nm --demangle /opt/osip2/lib/libosip2.so.10 | grep clock_gettime U clock_gettime 

It has an undefined clock_gettime symbol, which is provided by librt.so .

Well, actually it is a libosip2 developers error that their autotools does not work with --as-needed .

The communication command used by osip:

 libtool: link: gcc -shared -fPIC -DPIC .libs/ict_fsm.o .libs/ist_fsm.o .libs/nict_fsm.o .libs/nist_fsm.o .libs/ict.o .libs/ist.o .libs/nict.o .libs/nist.o .libs/fsm_misc.o .libs/osip.o .libs/osip_transaction.o .libs/osip_event.o .libs/port_fifo.o .libs/osip_dialog.o .libs/osip_time.o .libs/port_sema.o .libs/port_thread.o .libs/port_condv.o -Wl,-rpath -Wl,/home/arif/sak/osip/src/osipparser2/.libs -Wl,-rpath -Wl,/opt/osip2-test/lib -lnsl ../osipparser2/.libs/libosipparser2.so -Wl,-soname -Wl,libosip2.so.10 -o .libs/libosip2.so.10.0.0 

Thus, it does not bind to librt and therefore does not list librt in its NEEDED list

If configured with

  LDFLAGS="${LDFLAGS} -lrt" ./configure --prefix=/opt/osip2-test/ 

Then the link command will be:

 libtool: link: gcc -shared -fPIC -DPIC .libs/ict_fsm.o .libs/ist_fsm.o .libs/nict_fsm.o .libs/nist_fsm.o .libs/ict.o .libs/ist.o .libs/nict.o .libs/nist.o .libs/fsm_misc.o .libs/osip.o .libs/osip_transaction.o .libs/osip_event.o .libs/port_fifo.o .libs/osip_dialog.o .libs/osip_time.o .libs/port_sema.o .libs/port_thread.o .libs/port_condv.o -Wl,-rpath -Wl,/home/arif/sak/osip/src/osipparser2/.libs -Wl,-rpath -Wl,/opt/osip2-test/lib -lnsl ../osipparser2/.libs/libosipparser2.so -lrt -Wl,-soname -Wl,libosip2.so.10 -o .libs/libosip2.so.10.0.0 

So, its connection with librt . His is also reflected in his ELF:

 arif@khost :~/sak/osip/src/osip2/.libs$ objdump -p libosip2.so.10 | grep NEEDED NEEDED libosipparser2.so.10 NEEDED librt.so.1 NEEDED libc.so.6 

This patch fixes this:

 diff --git a/src/osip2/Makefile.am b/src/osip2/Makefile.am index bb0d8f3..b72c22a 100644 --- a/src/osip2/Makefile.am +++ b/src/osip2/Makefile.am @@ -14,7 +14,7 @@ libosip2_la_SOURCES+=port_sema.c port_thread.c port_condv.c endif libosip2_la_LDFLAGS = -version-info $(LIBOSIP_SO_VERSION) \ - $(FSM_LIB) $(EXTRA_LIB) ../osipparser2/libosipparser2.la -no-undefined + $(FSM_LIB) $(EXTRA_LIB) ../osipparser2/libosipparser2.la -no-undefined -lrt INCLUDES = -I$(top_srcdir)/includ 

Usenet relevant discussion discussion: https://groups.google.com/forum/#!topic/comp.unix.programmer/VKbARy6W4AY

UPDATE:

The osip developer answered my mail. He fixed it with another patch (a more general solution than mine) http://git.savannah.gnu.org/cgit/osip.git/commit/?id=bd5b1ad58381e4bfce08bad9b66ad00cd28f9b65