I link a shared library on the command line while building an executable. Running ldd on that executable is not showing the linked shared library.
After looking at some of the output of the linker, I have even tried adding the -Wl,--no-as-needed option and that didn't help either.
foo.c:
#include <stdio.h>
void foo () {
printf ("Hello world\n");
}
main.c:
#include <stdio.h>
int main () {
printf ("In main \n");
foo ();
}
Here's the command I used to compile and link:
$ gcc -Wl,--no-as-needed main.c -o main -L./ -lfoo
/bin/ld: cannot find -lfoo
collect2: error: ld returned 1 exit status
$ gcc -c foo.c -shared -Wl,-soname,libfoo.so -o libfoo.so
$ ls -l libfoo.so
-rw-r--r-- 1 apple eng 1488 Jun 4 04:44 libfoo.so
$ gcc -Wl,--no-as-needed main.c -o main -L./ -lfoo
$ ldd main
linux-vdso.so.1 => (0x00007fffbdd6c000)
libc.so.6 => /lib64/libc.so.6 (0x00007f6367e23000)
/lib64/ld-linux-x86-64.so.2 (0x00005556e268a000)
libfoo.so does not show up above.
$ objdump -x main | grep NEEDED
NEEDED libc.so.6
Why isn't libfoo.so showing up as NEEDED?
By using the gcc option -c you're telling it to create only object from foo.c, so the only product you're getting from this gcc command is an object file. The fact that its suffix is .so is only because you forced it using -o option. If you run this command without -o you'd see that the output is just foo.o - an object file.
If you omit the -c from the gcc command you'd get the shared object you wanted.
Running file on the output file shows the difference (note that I'm not setting the output name using -o and letting gcc use its default names):
With -c:
> gcc -c foo.c -shared
> file foo.o
foo.o: ELF 64-bit LSB relocatable, x86-64, version 1 (SYSV), not stripped
Without -c:
> gcc foo.c -shared
> file a.out
a.out: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=a63581bfc45f845c501ffb6635, not stripped
^^^
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