At line 20 of main.c, check_rom() is called. Soon after, load_rom() is called at line 25.
This causes several problems:

check_rom() fopen()s a file and doesn't close it before returning, causing the open FILE to leak. Additionally, it unnecessarily makes any further attempt at opening the file implementation-defined behavior, although I don't know of a C implementation where opening the same file multiple times doesn't just work.

The load_rom() call also fopen()s the same file, without any checking of return values. A non-existing file is not the only cause for an error return of fopen().

Even if the above issues are fixed, there is an inherent TOCTTOU error in doing this. There is no guarantee that the file will still exist by the time load_rom() is called.

The fix is to get rid of the check_rom() function and check the return value of fopen() in load_rom().

As suggested by a oh5nxo on Reddit, the function load_rom() could be improved in the following way:

void load_rom(char* filename) {
    FILE* fp = fopen(filename, "rb");

    // read program size into memory
    fread(memory + 0x200, 1, sizeof(memory) - 0x200, fp);

    fclose(fp);
}

From a quick first test, it seems good. Waiting to update to give it a better look.

`
// FX55: Stores V0 through Vx (Vx included) in memory starting
// at addr I.
case 0x0055:
debug_print("[OK] 0x%X: FX55\n", op);

                for (int i = 0; i <= x; i++) {
                    V[i] = memory[I + i];
                }

                pc += 2;
                break;

`

shouldn't this segment of code be like this:

`// FX55: Stores V0 through Vx (Vx included) in memory starting
// at addr I.
case 0x0055:
debug_print("[OK] 0x%X: FX55\n", op);

                for (int i = 0; i <= x; i++) {
                    memory[I + i] = V[i];
                }

                pc += 2;
                break;`