cool_div.c

// We do a little too much trolling...
//
// Ever wanted to pretend divisions by zero just didn't happen? here you go...
// this is memes, don't try to make this work with C because the optimizer will
// fight you on it. You can apply it to your own language if you really wanted.
#include <stdint.h>
#include <stdio.h>

#define WIN32_LEAN_AND_MEAN
#include <windows.h>

static LONG cool_division(EXCEPTION_POINTERS* e) {
    if (e->ExceptionRecord->ExceptionCode == EXCEPTION_INT_DIVIDE_BY_ZERO) {
        uint8_t* rip = (uint8_t*) e->ExceptionRecord->ExceptionAddress;

        // first byte is either 0xF6 or 0xF7 for IDIV or DIV
        if (rip[0] != 0xF7 && rip[0] != 0xF6) {
            return EXCEPTION_CONTINUE_SEARCH;
        }

        // so we need a mini x86 decoder now... it's
        // just for the basic ModRM logic and we don't
        // need to read sizes, just length so we can skip.
        size_t len = 2;
        uint8_t mod = rip[1] >> 6, rm = rip[1] & 7;
        if (rm == 4) {
            uint8_t sib = rip[len++];
            if (mod == 0 && (sib & 7) == 5) {
                // indirect disp32
                mod = 2;
            }
        } else if (mod == 0 && rm == 5) {
            len += 4; // RIP-relative
        }

        if (mod == 1) { // disp8
            len += 1;
        } else if (mod == 2) { // disp32
            len += 4;
        }

        // skip the instruction
        e->ContextRecord->Rip = (DWORD64) &rip[len];

        // zero out the results
        e->ContextRecord->Rdx = 0;
        e->ContextRecord->Rax = 0;
        return EXCEPTION_CONTINUE_EXECUTION;
    }

    return EXCEPTION_CONTINUE_SEARCH;
}

int main() {
    AddVectoredExceptionHandler(1, cool_division);

    int a = 0;
    int b = 16 / a;

    printf("Result = %d\n", b);
    return 0;
}