Creating a shared library from a static library using GNU toolchain (gcc/ld)

Question

I am having trouble generating a shared object from a static library. While I know there are other alternatives, I am now bothered (as opposed to stuck) by why this isn't working and how to make it work.

Below is very simple source code I am using.

get_zero.c

#include "get_zero.h"

int
get_zero(void)
{
        return 0;
}

get_zero.h

int get_zero(void);

main.c

#include <stdio.h>
#include <string.h>

#include "get_zero.h"

int
main(void)
{
    return get_zero();
}

The goal is create two functionally equal applications using libget_zero_static and libget_zero_shared.

Here are my compilation/linking steps:

gcc -c -fPIC get_zero.c
ar cr libget_zero_static.a get_zero.o
gcc -shared -o libget_zero_shared.so -L. -Wl,--whole-archive -lget_zero_static -Wl,-no--whole-archive

And this is the error I get:

/usr/bin/ld: cannot find -lgcc_s
/usr/bin/ld: /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libc.a(init-first.o): relocation R_X86_64_32 against `_dl_starting_up' can not be used when making a shared object; recompile with -fPIC
/usr/lib/gcc/x86_64-linux-gnu/4.6/../../../x86_64-linux-gnu/libc.a(init-first.o): could not read symbols: Bad value
collect2: ld returned 1 exit status

This is on a 64-bit Ubuntu system.

I read about the whole-archive option here, and it seemed like this questions should have removed all of my road blocks. How to create a shared object file from static library.

Solution 1

It seems you need to specify the archive as an argument, not as a library. So make that libget_zero_static.a instead of -lget_zero_static. At least it works for me this way:

gcc -shared -o libget_zero_shared.so \
-Wl,--whole-archive                  \
libget_zero_static.a                 \
-Wl,--no-whole-archive

Solution 2

You can just try another way: link twice, once for static lib, and the other for shared lib. That should be easier and more common.

Comments

[user442585]

Yes. That would be the normal route to go, but as I stated comments I think this method should be possible. I just don't understand why it isn't working.

[user442585]

This did not fix the issue for me. Are you running 32-bit? I am pretty sure this did work for me on a 32-bit system.

[MvG]

@user442585: 64 bit using gcc 4.6.3 and ld 2.23. Also works using several other gcc versions, so I'd say it might be due to the ld version. What error do you get? Same one as you pasted in your question? Could the -fPIC from the compiler flags have gotten lost this time?

[user442585]

Never figured this one out, oh well..... You put in the most effort so you get the answer credit :)