Shared library and rpath

Question

I cannot make rpath work properly and make my binary to search for the library in the specified folder:

I have 3 very simple files:

main.c

#include <stdio.h>
#include <func.h>
int main() {
    testing();
return 1;
}

func.h

void testing();

func.c

#include "func.h"
void testing(){

    printf(testing\n");
}

Then I proceed to create a shared library as it follows:

gcc -c -fpic func.c -o ../release/func.o
gcc -shared -o ../release/lib/lib_func.so ../release/func.o

And then compile the program:

gcc main.c ../release/lib/lib_time_mgmt.so -Wl,-rpath=/home/root/ -o ../release/main

I receive the next warning:

main.c:7:2: warning: implicit declaration of function ‘testing’ [-Wimplicit-function-declaration]
testing();

But besides it, the program works fine.

However, my problem is that if now I want to move the library to /home/root (as specified in rpath) it does not work and the library is still searched only in the path specified when I compiled the main.c file which is ../release/lib/lib_time_mgmt.so

What am I doing wrong?

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EDIT: After accepting the answer, I leave here the exact line as I used it and made it work for whoever might find it useful:

gcc main.c -L/home/root -Wl,-rpath,'/home/root/' -l:libtime_mgmt -o ${OUT_FILE}

Note: the rpath was used with the path betwen simple '. Not sure if that was the reason why it was not working before, but it worked this way now.

Answer 1

rpath is not used at compile time, but rather at link/runtime... thus you probably need to use both of these:

• -L /home/root - to link correctly at build time
• -Wl,-rpath=/home/root - to link correctly at run-time

You should use the -l ${lib} flag to link with libraries, don't specify their path as an input.

In addition to this, convention states that the libraries are named libNAME.so - e.g:

• -l func will try to link with libfunc.so
• -l time_mgmt will try to link with libtime_mgmt.so

Once you've addressed the above points, try the following:

gcc main.c -L/home/root -Wl,-rpath=/home/root -lfunc -ltime_mgmt -o ${OUT_FILE}

As a final point, I'd advise that you try not to use rpath, and instead focus on installing libraries in the correct places.

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Unrelated to your question, but worth noting. Your use of #include <...> vs #include "..." is questionable. See: What is the difference between #include <filename> and #include "filename"?