linux

Using attribute((weak)) weak symbols in gcc compilation of dynamic library so on Linux system

18.08.2026 0, ? Design & Development

First explain the code structure: there are three source files, two dynamic library so sources: lib1.c and lib2.c, each exporting one library function (gcc exports by default, unlike Windows msvc which requires explicit dllexport), and one main program source: main.c, which calls the exported functions of the two dynamic libraries, as follows:

lib1.c

#include <stdio.h>

void lib1_func(const char* from)
{
        printf("lib1 func from %s\n", from);
}

lib2.c

#include <stdio.h>

void lib2_func(const char* from)
{
        printf("lib2 func from %s\n", from);
}

main.c

#include <stdio.h>

void lib1_func(const char* from);
void lib2_func(const char* from);

int main()
{
        printf("hello from main\n");
        lib1_func("main");
        lib2_func("main");
        return 0;
}
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Method to compile 32bit programs on 64bit Linux CentOS 7

12.08.2026 0, ? Design & Development

The method recorded here theoretically applies to all RedHat‑based Linux distributions!
Normally on 64bit Linux (after installing gcc and related tools), compiled executables target the 64bit environment. If you want to compile for 32bit (which can also run on 64bit systems), just add the -m32 option to gcc (for ld there is a corresponding -melf_i386). Although compiling only requires adding the parameter, you still need to install the 32bit versions of the C and C++ standard libraries.

For example, if you compile directly with -m32, you will get the following error:

[kres@localhost test6432]$ gcc -m32 test.c
In file included from /usr/include/features.h:399:0,
from /usr/include/unistd.h:25,
from /usr/include/usb.h:28,
from test.c:1:
/usr/include/gnu/stubs.h:7:27: fatal error: gnu/stubs-32.h：No such file or directory

# include ;
^
compilation terminated.
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