Linux 尽管给出了 `-lrt`，但未定义对 `clock_gettime` 的引用
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Undefined reference to `clock_gettime` although `-lrt` is given
提问by Aftnix
I've give -lrtas the last linker flag to the compiler. But still getting this error.
我已将-lrt最后一个链接器标志提供给编译器。但仍然收到此错误。
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 man page says :
手册页说：
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 kind of confused where i'm doing it wrong.
所以我有点困惑我在哪里做错了。
I've tried to read symbols in librt.sowith no luck :
我试图在librt.so没有运气的情况下阅读符号：
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 1The reason i can't read symbols out of librt.sois that they are "stripped". Where can i get the symbol names ?
更新 1我无法读取符号的原因librt.so是它们被“剥离”了。我在哪里可以得到符号名称？
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
更新 2
Well things become very confusing because the following test code compiles and runs just fine :
好吧，事情变得非常混乱，因为以下测试代码编译并运行得很好：
#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
内置
arif@khost:~/sak/sak.exosip$ gcc what.c -lrt
UPDATE3The code i'm trying compile :
UPDATE3我正在尝试编译的代码：
#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;
}
采纳答案by Aftnix
Well the problem is solved If i pass this linker flag
那么问题就解决了如果我通过这个链接器标志
-Wl,--no-as-needed
Before the library list in command line.
在命令行中的库列表之前。
Why this works because in my platform, linker is always passed with -Wl,--as-needed.
为什么这有效，因为在我的平台中，链接器总是通过-Wl,--as-needed.
From ldmanual :
从ld手册：
--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.
So when --as-neededis given before a library , liker only links with the libraries which are given in NEEDEDsection of the library.
因此，当--as-needed在 library 之前给出时，liker 仅与图书馆部分中给出NEEDED的图书馆链接。
For example,
例如，
-Wl,--as-needed -llibA -llibB -llibC
Here --as-needed is given before libA. So during linking, linker will examine the NEEDEDsection of libA. If in NEEDEDsection of libAlists only libC, then the libBwill not be linked.
这里 --as-needed 之前给出libA。所以在连接时，连接器将检查NEEDED的部分libA。如果仅在列表的NEEDED部分中，则不会链接。libAlibClibB
This specific problem occurred because
出现此特定问题是因为
arif@khost:~/sak/sak.exosip$ objdump -p /opt/osip2/lib/libosip2.so.10 | grep NEEDED
NEEDED libosipparser2.so.10
NEEDED libc.so.6
libosip2does not lists librtas NEEDED.
libosip2不librt列为NEEDED。
If i pass --no-as-needed, then all the libraries will be linked regardless of what is given in ELF's NEEDEDsection.
如果我通过--no-as-needed，那么无论 ELFNEEDED部分中给出了什么，所有库都将被链接。
Although this should not be the case because,
虽然情况不应该是这样，因为，
arif@khost:~/sak/sak.exosip$ nm --demangle /opt/osip2/lib/libosip2.so.10 | grep clock_gettime
U clock_gettime
It has undefined symbol clock_gettimewhich is provided by librt.so.
它有未定义的符号clock_gettime，由librt.so.
Well its actually a fault of the libosip2devs that their autotoolsis not working with --as-needed.
那么它实际上是一个错误libosip2的开发者，他们autotools不与工作--as-needed。
The link command used by osip:
osip 使用的链接命令：
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
So its not linking with librtand thats why its not listing librtin its NEEDEDlist
所以它没有链接，librt这就是为什么它没有列librt在它的NEEDED列表中
If configured with :
如果配置为：
LDFLAGS="${LDFLAGS} -lrt" ./configure --prefix=/opt/osip2-test/
Then the link command becomes :
然后链接命令变为：
libtool: link: gcc -shared -fPIC -DPIC .libs/ict_fsm.o .libs/ist_fsm.o .libs/nict_fsm.o .libs/nist_fsm.o .libs/ict.o .libs/ist.o .libs/nict.o .libs/nist.o .libs/fsm_misc.o .libs/osip.o .libs/osip_transaction.o .libs/osip_event.o .libs/port_fifo.o .libs/osip_dialog.o .libs/osip_time.o .libs/port_sema.o .libs/port_thread.o .libs/port_condv.o -Wl,-rpath -Wl,/home/arif/sak/osip/src/osipparser2/.libs -Wl,-rpath -Wl,/opt/osip2-test/lib -lnsl ../osipparser2/.libs/libosipparser2.so -lrt -Wl,-soname -Wl,libosip2.so.10 -o .libs/libosip2.so.10.0.0
So its linking with librt. Its also reflected in its ELF:
所以它与librt. 它也反映在它的 ELF 中：
arif@khost:~/sak/osip/src/osip2/.libs$ objdump -p libosip2.so.10 | grep NEEDED
NEEDED libosipparser2.so.10
NEEDED librt.so.1
NEEDED libc.so.6
This patch fixes this :
这个补丁修复了这个：
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
Relevant usenet discussion thread : https://groups.google.com/forum/#!topic/comp.unix.programmer/VKbARy6W4AY
相关usenet讨论线程：https://groups.google.com/forum/#! topic/comp.unix.programmer/VKbARy6W4AY
UPDATE:
更新：
osip developer responded to my mail. He fixed it with a different patch (More general solution then mine) http://git.savannah.gnu.org/cgit/osip.git/commit/?id=bd5b1ad58381e4bfce08bad9b66ad00cd28f9b65
osip 开发人员回复了我的邮件。他用不同的补丁修复了它（比我的更通用的解决方案） http://git.savannah.gnu.org/cgit/osip.git/commit/?id=bd5b1ad58381e4bfce08bad9b66ad00cd28f9b65
