From Newsgroup: comp.lang.c++

On 28/08/2025 17:12, pozz wrote:

I don't think this is a pure C programming question, but it's related.

I'm building a static library mylib.a with all the object files except main.o, and the final executable linking together main.o and mylib.a.

I want to remove from the final exe everything present in mylib.a that
is not used in main.o.

Suppose only mod1.o is present in mylib.a. foo1() and bar1() are defined
in mod1.c. main() is the only function in main.c and only foo1() is
called from main().

gcc -O2 -ffunction-sections -fdata-sections -c -o mod1.o mod1.c
ar rcs mylib.a mod1.o
gcc -O2 -ffunction-sections -fdata-sections -c -o main.o main.c
gcc -Wl,--gc-sections,--print-gc-sections -o main[.exe] main.o mylib.a objdump -d main[.exe] | grep bar1

MinGW in Windows build a main.exe that contains bar1(), while gcc in WSL doesn't.

Why?

I am not sure whether you are creating a DLL file for your library. I
ask this because you mentioned "final exe" which implies Windows
executable file that uses DLL file.

Step 1 is to create and compile your library source code:

// mycode.c
#include <stdio.h>

// Exported function
__declspec(dllexport) void hello() {
printf("Hello from DLL!\n");
}


Step 2: compile it like so:

gcc -shared -o mydll.dll mycode.c


Step 3: create a header file:
// mycode.h
#ifndef MYCODE_H
#define MYCODE_H

__declspec(dllimport) void hello();

#endif

Step 4: Create an import library for linking:

gcc -c mycode.c
gcc -shared -o mydll.dll mycode.o -Wl,--out-implib,libmydll.a


Step 5: Create a client to use your DLL

// main.c
#include "mycode.h"

int main() {
hello();
return 0;
}


Step 6: Compile client to create main.exe file:

gcc main.c -L. -lmydll -o main.exe


These are all commands in few lines:

# Compile and create DLL
gcc -c mycode.c
gcc -shared -o mydll.dll mycode.o -Wl,--out-implib,libmydll.a

# Compile and link client
gcc main.c -L. -lmydll -o main.exe

This should work but is a streamlined version for this discussion.

Good luck.




--- Synchronet 3.21a-Linux NewsLink 1.2