dlopen missing shared lib twice returns nonzero result in non-debug builds

[hoodmane]

Source file:

#include <dlfcn.h>
#include <stdio.h>

int main() {
    void* res = dlopen("a", RTLD_NOW);
    printf("res: %p\n", res);
    res = dlopen("a", RTLD_NOW);
    printf("res: %p\n", res);
    return 0;
}

Compile and run:

emcc a.c -sMAIN_MODULE=2
node a.out.js

behaves sort of as expected:

Error in loading dynamic library a: Error: ENOENT: no such file or directory, open '/home/rchatham/Documents/programming/emscripten/a'
res: 0
Aborted(Assertion failed: Attempt to load 'a' twice before the first load completed)
Error in loading dynamic library a: RuntimeError: Aborted(Assertion failed: Attempt to load 'a' twice before the first load completed)
res: 0

Even here I am concerned that if I later created a file called "a" which was a valid shared library, it would not succeed in opening it. Whereas native dlopen would work. But this isn't causing trouble.

The problem is if we compile with -O1, then it does not fail on the second call:

$ emcc a.c -sMAIN_MODULE=2 -O1
$ node a.out.js
res: 0
res: 0x10ef0

This is troublesome.

Version of emscripten/emsdk:

$ emcc -v
emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 3.1.72-git (b2ced9de42ea8028233d7d3588c45ce837b61185)
clang version 20.0.0git (https:/github.com/llvm/llvm-project 50866e84d1da8462aeb96607bf6d9e5bbd5869c5)
Target: wasm32-unknown-emscripten
Thread model: posix