Least common multiple and gcd in assembly

Question

I'm trying to write a program, which calculates lcm and gcd of two unsigned longs in assembly x86-64, but I get some floating point error, when I'm launching my program. The error is in polish, but I can translate it into "Floating point operations error".

Here is the code:

    .global lcm_gcd
        .type lcm_gcd,@function

        .section .text

lcm_gcd:
        mult = %rdx
        mov %rdi, %rax
        mul %rsi
        mov %rax, mult

.comp:
        cmp %rdi, %rsi      # gcd
        je .found
        jb .secPos
        sub %rdi, %rsi
        jmp .comp

.secPos:        # %rdi > %rsi <==> x > y
        sub %rsi, %rdi

        jmp .comp

.found:
        div %rdi

        ret

        .size   lcm_gcd, . - lcm_gcd

And the test program in C:

    #include <stdio.h>
#include <stdlib.h>

typedef struct {
    unsigned long lcm, gcd;
} result_t;

result_t lcm_gcd(unsigned long x, unsigned long y);

int main(int argc, char **argv) {
    result_t r = lcm_gcd(atol(argv[1]), atol(argv[2]));
    printf("%lu, %lu\n", r.lcm, r.gcd);

    return 0;
}