Assembly Language for Beginners

6.1. ARGUMENTS PASSING METHODS (CALLING CONVENTIONS)

mov DWORD PTR [rsp+32], eax

mov r9d, DWORD PTR c$[rsp]

mov r8d, DWORD PTR b$[rsp]

mov edx, DWORD PTR a$[rsp]

lea rcx, OFFSET FLAT:$SG2937

call printf

add rsp, 72
ret 0
f1 ENDP

Here we clearly see how 7 arguments are passed: 4 via registers and the remaining 3 via the stack.

The code of the f1() function’s prologue saves the arguments in the “scratch space”—a space in the stack
intended exactly for this purpose.

This is arranged so because the compiler cannot be sure that there will be enough registers to use without
these 4, which will otherwise be occupied by the arguments until the function’s execution end.

The “scratch space” allocation in the stack is the caller’s duty.

Listing 6.7: Optimizing MSVC 2012 /0b

$SG2777 DB '%d %d %d %d %d %d %d', 0aH, 00H

a$ = 80
b$ = 88
c$ = 96
d$ = 104
e$ = 112
f$ = 120
g$ = 128
f1 PROC
$LN3:
sub rsp, 72

mov eax, DWORD PTR g$[rsp]

mov DWORD PTR [rsp+56], eax

mov eax, DWORD PTR f$[rsp]

mov DWORD PTR [rsp+48], eax

mov eax, DWORD PTR e$[rsp]

mov DWORD PTR [rsp+40], eax

mov DWORD PTR [rsp+32], r9d

mov r9d, r8d

mov r8d, edx

mov edx, ecx

lea rcx, OFFSET FLAT:$SG2777

call printf

add rsp, 72
ret 0
f1 ENDP

main PROC
sub rsp, 72

mov edx, 2

mov DWORD PTR [rsp+48], 7

mov DWORD PTR [rsp+40], 6

lea r9d, QWORD PTR [rdx+2]

lea r8d, QWORD PTR [rdx+1]

lea ecx, QWORD PTR [rdx-1]

mov DWORD PTR [rsp+32], 5

call f1

xor eax, eax
add rsp, 72
ret 0
main ENDP