Unique shared library issues

Problem description

Recently, when I tried to link a self-built C language shared library to a local project, I encountered a link error and prompted "Undefined reference". The error message is as follows:

 <code>/bin/ld: /tmp/cchb7mj8.o: in function `sdl_main': main.c:(.text 0x3c): undefined reference to `sdl_enterappmaincallbacks' ... (其他类似的未定义引用) ... collect2: error: ld returned 1 exit status make: *** [makefile:7: all] error 1</code>

Troubleshooting process

Trying to recompile the library multiple times and trying different methods, none of them worked. After searching for relevant information on search engines, I found that someone encountered similar problems in a forum, but was using a 32-bit toolchain, while my toolchain was 64-bit. After excluding toolchain version differences, consider trying different compilers.

Solution

The problem was solved after initially compiling using GCC and switching to Clang.

Problem recurrence and analysis

To understand the root cause of the problem, a simple test project was created:

• lib.h:

 <code class="language-c">#pragma once int add(int a, int b);</code>

• lib.c:

 <code class="language-c">#include "lib.h" int add(int a, int b) { return ab; }</code>

• main.c:

 <code class="language-c">#include "lib.h" #include <stdio.h> int main () { printf("4 3=%d\n", add(4, 3)); return 0; }</stdio.h></code>

• build_so.sh (Clang compiles shared library):

 <code class="language-bash">clang -std=c11 -c -o lib.o lib.c clang -shared -fpic -o libm.so lib.o</code>

• build_main.sh (GCC compiles the main program, links to the shared library):

 <code class="language-bash">gcc -std=c11 -L. -l:libm.so main.c -o main</code>

Using the above script, the link failed with a similar "Undefined Reference" error:

 <code>/bin/ld: /tmp/ccymm8ki.o: in function `main': main.c:(.text 0x13): undefined reference to `add' collect2: error: ld returned 1 exit status</code>

However, if the compilers in build_so.sh and build_main.sh are interchangeable (i.e. using GCC to compile the shared library and Clang compiles the main program), the link is successful.

in conclusion

This issue may be related to the differences in internal symbol handling between compilers when generating and linking shared libraries. When building shared libraries and executables with different compilers, you need to ensure that they are compatible. While this problem can be avoided in most cases using the same compiler, this example illustrates potential compatibility issues between different compilers. If you need to use different compilers in your project, you need to double-check and make sure that symbolic parsing is done correctly between them.

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