GCC: Shield dependencies between dynamic libraries

Assume a program with the following dependencies:

m depends on a

a depends on b

//a.c#include void b();void a(){printf("Here is a call b\n");b();

//b.c#include void b(){printf("Here is b\n");

//m.c#include void a();int main(){a();return 0;

GCC: Compile-time library path and runtime library path - Programmer Sought

It has been stated that this program should compile and link.

But there is a place that is not very convenient, that is, m only depends on a on the surface, but it needs to add the b that a depends on when compiling and linking, so that it can run.For a more complex program, it is necessary to constantly check the program to confirm what the libraries that need to be compiled and linked finally have, and it is inconvenient.

Then is it possible to put the dependencies of a into the compilation process of a:

gcc -fpic -shared a.c -o liba.so -lb -L .

gcc -o m m.c -la -L.

Because library a needs library b when connecting, but cannot find it, an error is reported:
/usr/bin/ld: warning: libb.so, needed by ./liba.so, not found (try using -rpathor -rpath-link)
/usr/bin/ld: ./liba.so: undefined reference to `b'
collect2: error: ld returned 1 exit status

ldd liba.so
linux-vdso.so.1 (0x00007ffecb1fd000)
libb.so => ​​not found
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f2ba19ad000)
/lib64/ld-linux-x86-64.so.2 (0x00007f2ba1bb7000)

It can be seen that this method does not work.

This problem can be solved by -Wl,-rpath=

-WL: Indicates that the compiler will pass the following parameters to the linker ld

-rpath: The path used to specify the compile link and runtime dependencies

Therefore, when compiling a, you can add the b it depends on in the following way:

gcc -fpic -shared a.c -o liba.so -lb -Wl,-rpath=.

gcc -o m m.c -la -L .

Note: After the above compilation, an error may be reported at runtime:

./m: error while loading shared libraries: liba.so: cannot open shared object file: No such file or directory

The reason is that liba.so cannot be found at runtime
There are two ways to solve this problem:

1. By setting LD_LIBRARY_PATH

export LD_LIBRARY_PATH=./:$LD_LIBRARY_PATH

2. Also specify when compiling m -Wl,-rpath=, that is:

gcc -o m m.c -la -Wl,-rpath=.