How functions are called in 32-bit x86 Assembly

1. callingFunctions.S
Passing arguments to functions via the stack

2. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
8(%esp) argv
4(%esp) argc
(%esp) return addr
%esp 28ff2c %ebp old %ebp %eax $0

3. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
8(%esp) argv
4(%esp) argc
(%esp) return addr
%esp 28ff2c %ebp old %ebp %eax $0

4. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
12(%esp) argv
8(%esp) argc
4(%esp) return addr
(%esp) old %ebp
%esp 28ff28 %ebp old %ebp %eax $0

5. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
12(%esp) argv
8(%esp) argc
4(%esp) return addr
(%esp) old %ebp
%esp 28ff28 %ebp old %ebp %eax $0

6. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
%esp 28ff28 %ebp 28ff28 %eax $0

7. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
%esp 28ff28 %ebp 28ff28 %eax $0

8. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
%esp 28ff20 %ebp 28ff28 %eax $0

9. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
%esp 28ff20 %ebp 28ff28 %eax $0

10. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp)
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax $0

11. LC0:
.ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp)
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax $0

12. .ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp)
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax $0

13. .ascii "The argument was %d120"
.text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax $0

14. .text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax $0

15. .text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax argv

16. .text
.globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax argv
Address of
pointer to
prog name

17. .globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax argv
Address of
pointer to
prog name

18. .globl _main
.def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax argv+4
Address of
pointer to
first arg

19. .def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax argv+4
Address of
pointer to
first arg

20. .def _main; .scl 2; .type 32; .endef
_main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax argv[1]
pointer to
first arg

21. _main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) %esp 28ff00 %ebp 28ff28 %eax argv[1]

22. _main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax argv[1]

23. _main:
pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
For our purposes
argv[1] = "67"
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax argv[1]

24. pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
For our purposes
argv[1] = "67"
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax argv[1]

25. pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
For our purposes
argv[1] = "67"
_atoi grabs the char array at
the address stored in (%esp),
converts the ASCII string to an
int, and returns the int in %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax argv[1]

26. pushl %ebp
movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
For our purposes
argv[1] = "67"
_atoi grabs the char array at
the address stored in (%esp),
converts the ASCII string to an
int, and returns the int in %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax $67

27. movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $1234
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax $67

28. movl %esp, %ebp
andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax $67

29. andl $-16, %esp
subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax $67

30. subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp)
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax $67

31. subl $32, %esp
call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp) $67
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax $67

32. call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
leave
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp) $67
(%esp) argv[1] %esp 28ff00 %ebp 28ff28 %eax $67

33. call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
leave
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp) $67
(%esp) $LC0 %esp 28ff00 %ebp 28ff28 %eax $67

34. call ___main
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
leave
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp) $67
(%esp) $LC0
$LC0 is the location in memory
of our format string.
"The argument was %d120"
%esp 28ff00 %ebp 28ff28 %eax $67

35. movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
leave
ret
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp) $67
(%esp) $LC0 %esp 28ff00 %ebp 28ff28 %eax $67
$LC0 is the location in memory
of our format string.
"The argument was %d120"

36. movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
leave
ret
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp) $67
(%esp) $LC0 %esp 28ff00 %ebp 28ff28 %eax $67

37. movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
leave
ret
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp) $67
(%esp) $LC0 %esp 28ff00 %ebp 28ff28 %eax $0

38. movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
leave
ret
12(%ebp) argv
8(%ebp) argc
4(%ebp) return addr
(%ebp) old %ebp
28(%esp) $67
24(%esp)
20(%esp)
16(%esp)
12(%esp)
8(%esp)
4(%esp) $67
(%esp) $LC0 %esp 28ff00 %ebp 28ff28 %eax $0

39. movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
leave
ret
8(%esp) argv
4(%esp) argc
(%esp) return addr
%esp 28ff2c %ebp old %ebp %eax $0

40. 8(%esp) argv
4(%esp) argc
(%esp) return addr
%esp 28ff2c %ebp old %ebp %eax $0
movl $1234, 28(%esp)
movl 12(%ebp), %eax
addl $4, %eax
movl (%eax), %eax
movl %eax, (%esp)
call _atoi
movl %eax, 28(%esp)
movl 28(%esp), %eax
movl %eax, 4(%esp)
movl $LC0, (%esp)
call _printf
movl $0, %eax
leave
ret

41. callingFunctions.S
Passing arguments to functions via the stack
This presentation by Pat Hawks is licensed under a
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