Some basic assembly functions

Wed, 03 Jun 2026 00:00:00 +0000

Will add more in the future but just gonna write some basic assembly to show you what it might look like.

Factorials and Rescursive functions Link to heading

Below is a demonstration of how to calculate the factorial of a number pushed onto the stack in x86 assembly, the x86_64 will be below

 1; calculate the factorial
 2; 3! = 3 * 2 * 1
 3
 4; x86 32 bit example
 5
 6.section .data
 7
 8.section .text
 9.globl _start
10.globl factorial
11
12_start:
13 pushl $4 ; push argument (factorial 4)
14 call factorial
15 addl $4, %esp ; scrub parameter, always return SP to where it was before
16 ; we called a function
17 movl %eax, %ebx ; store in ebx as our return status
18
19 movl $1, %eax
20 int $0x80
21
22.type factorial, @function
23factorial:
24 pushl %ebp ; push so we can restore ebp afterwards
25 movl %esp, %ebp ; we dont want to modify the SP so we push it to ebp
26 movl 8(%ebp), %eax
27 cmpl $1, %eax
28 je end_factorial
29 decl %eax
30 pushl %eax ; push it for our call to factorial
31 call factorial
32 movl 8(%ebp), %ebx ; reload our parameter in %ebx
33 imull %ebx, %eax
34
35end_factorial:
36 movl %ebp, %esp ; restoring ebp and esp to where
37 popl %ebp ; they were before the function started
38
39 ret

 1; calculate the factorial
 2; 3! = 3 * 2 * 1
 3
 4; x86_64 64bit example
 5
 6.section .data
 7
 8.section .text
 9.globl _start
10.globl factorial
11
12_start:
13 movl $5, %rdi
14 call factorial
15 mov %rax, %rdi
16 jmp exit
17
18.type factorial, @function
19factorial:
20 movl %rdi, %rax
21 cmpl $1, %rax
22 je end_factorial
23 decl %rax
24 movl %rax, %rdi
25 call factorial
26 movl %rax, %rbx
27 imull %rbx, %rax
28
29exit:
30 ret

more to come…

Assembly on Sable Ayala

Some basic assembly functions

Factorials and Rescursive functions Link to heading