NASM - asembler

NASM - asembler
✦
✦
✦
✦
http://sourceforge.net/projects/nasm/files/
Netwide Assembler – składnia Intela
B – byte; W – słowo (2B); D – podwójne słowo (4B); Q- 8B; T – 10B
Inicjalizuj lokację: DB, DW, DD, DQ, DT
✦ L6 DD 1A92H ; podwójne słowo pod L6 o wartości 1A92H
✦ Zarezerwuj lokację: RESB, RESW, RESD, RESQ, REST
✦ BUFFER RESB 64 ; zarezerwuj 64B pod BUFFER
✦ Włącz plik binarny: INCBIN
✦ INCBIN ’’file.dat” ; włącz plik file.dat
✦ Definiuj stałą: EQU
✦ MSGLEN EQU 25 ; stała MSGLEN równa liczbie dziesiętnej 25
✦ Powtórz instrukcję: TIMES
✦ ZEROBUF TIMES 64 DB 0 ; zainicjuj 64B w ZEROBUF na zero
✦
✦
✦
✦
✦
Definicja startu/końca sekcji: START/END
Definicja startu sekcji/dummy kontrolnej: CSECT/DSECT
Definicja rejestru bazowego: USING
Kompilacja warunkowa: IF, THEN, ELSE
Odwołanie zewnętrzne: EXTRN
NASM – makra
✦ Makro: MOV AX, A(8) generuje MOV AX, 1+2*8, gdzie
%DEFINE B(X) = 2*X
%DEFINE A(X) = 1 + B(X)
✦ &Makro
&MACRO PROLOGUE 1
PUSH
EBP
; push contents of EBP onto stack
; pointed to by ESP and
; decrement contents of ESP by 4
MOV EBP, ESP ; copy contents of ESP to EBP
SUB ESP, %1 ; substract first parameter value from ESP
✦ Wywołanie MYFUNC: PROLOGUE 12 generuje
MYFUNC: PUSH EBP
MOV EBP, ESP
SUB ESP,12
Przykład (Linux) - NASM
section
msg
.data
; data segment
db
"Hello, world!", 0x0a ; the string and newline char
section
global
.text
_start
; text segment
; Default entry point for ELF linking
_start:
; SYSCALL: write(1, msg, 14)
mov eax, 4
mov ebx, 1
mov ecx, msg
mov edx, 14
int 0x80
; put 4 into eax, since write is syscall #4
; put 1 into ebx, since stdout is 1
; put the address of the string into ecx
; put 14 into edx, since our string is 14 bytes
; Call the kernel to make the system call happen
; SYSCALL: exit(0)
mov eax, 1
mov ebx, 0
int 0x80
✦ nasm –f elf helloworld.asm
✦ ld helloworld.o
✦ ./a.out
; put 1 into eax, since exit is syscall #1
; exit with success
; do the syscall
Przykład (Cygwin) - NASM
; ---------------------------------------------------------------------------; fib.asm
;
; This is a Win32 console program that writes the first 40 Fibonacci numbers.
; It needs to be linked with a C library.
; http://www.cs.lmu.edu/~ray/notes/nasmexamples/
; ---------------------------------------------------------------------------global
extern
_main
_printf
section .text
_main:
push
ebx
; we have to save this since we use it
mov
xor
xor
inc
ecx, 40
eax, eax
ebx, ebx
ebx
; ecx will countdown from 40 to 0
; eax will hold the current number
; ebx will hold the next number
; ebx is originally 1
print:
; We need to call printf, but we are using eax, ebx, and ecx. printf
; may destroy eax and ecx so we will save these before the call and
; restore them afterwards.
Przykład (Cygwin) – NASM (c.d.)
push
push
eax
ecx
push
push
call
add
eax
format
_printf
esp, 8
pop
pop
ecx
eax
mov
mov
add
dec
jnz
edx, eax
eax, ebx
ebx, edx
ecx
print
; save the current number
; next number is now current
; get the new next number
; count down
; if not done counting, do some more
pop
ret
ebx
; restore ebx before returning
db
'%10d', 0
format:
✦ nasm –f win32 fib.asm
✦ gcc –o fib.exe fib.obj
NASM - przykłady
✦ http://www.nasm.us/doc/
✦ Win32
✦ nasm -fwin32 helloworld.asm
✦ gcc helloworld.obj
✦a
✦ Linux – usunąć podkreślenie: _
✦ nasm –felf –g helloworld.asm
✦ gcc helloworld.o
✦ gdb –q ./a.out
✦ set dis intel
✦ break _start
✦ run
global _main
extern _printf
section .text
_main:
push
_message
call
_printf
add
esp,4
ret
message: db ‘Hello, World’, 10, 0
NASM – wywołania w C
✦ nasm –felf maxoftree.asm
✦ gcc maxofthree.c maxofthree.o
✦ ./a.out
#include <stdio.h>
global maxofthree
section .text
int maxofthree(int, int, int);
int main() {
printf("%d\n", maxofthree(1, -4, -7));
printf("%d\n", maxofthree(2, -6, 1));
printf("%d\n", maxofthree(2, 3, 1));
printf("%d\n", maxofthree(-2, 4, 3));
printf("%d\n", maxofthree(2, -6, 5));
printf("%d\n", maxofthree(2, 4, 6));
return 0;
}
maxofthree:
mov eax, [esp+4]
mov ecx, [esp+8]
mov edx, [esp+12]
cmp eax, ecx
cmovl eax, ecx
cmp eax, edx
cmovl eax, edx
ret
NASM - int main(int argc, char** argv)
global main
extern printf
✦ gcc echo.o
✦ ./a.out
section .text
main:
mov
mov
ecx, [esp+4]
edx, [esp+8]
; argc
; argv
top:
push ecx
push edx
push dword [edx]
push format
call printf
add esp, 8
; save registers that printf wastes
pop
pop
; restore registers printf used
edx
ecx
add edx, 4
dec ecx
jnz top
ret
format:
db
'%s', 10, 0
; the argument string to display
; the format string
; remove the two parameters
; point to next argument
; count down
; if not done counting keep going
NASM - przykład
extern printf
global main
✦ nasm –elf
section .data
format: db
'%d', 10, 0
powers.asm
section .text
main:
✦ gcc powers.o
push esi
push edi
✦ ./a.out
mov esi, 1
✦ ebx, esi, edi, ebp, L1: mov edi, 31
push esi
ds, es, ss są
push format
call
printf
przechowywane
add esp, 8
add esi, esi
dla programu
dec edi
jne
L1
wywołującego
pop edi
pop
ret
esi
; callee-save registers
; current value
; counter
; push value to print
; push address of format string
; pop off parameters passed to printf
; double value
; keep counting
; restore callee-save registers
NASM a C
✦ nasm –elf -g
printl.asm
✦ gcc printl.o
✦ gdb -q ./a.out
✦ set dis intel
✦ list
✦ break 21
#include <stdio.h>
int main()
{
int a=5;
printf("a=%d, eax=%d\n", a, a+2);
return 0;
}
extern printf
global main
a:
fmt:
;the C function, to be called
; the standard gcc entry point
section .data
; Data section, initialized variables
dd
5
; int a=5;
db "a=%d, eax=%d", 10, 0 ; The printf format, "\n",'0'
section .text
main:
push
mov
ebp
ebp,esp
mov
add
push
push
push
call
add
mov
pop
mov
ret
eax, [a]
eax, 2
eax
dword [a]
dword fmt
printf
esp, 12
esp, ebp
ebp
eax,0
; Code section.
;the program label for the entry point
; set up stack frame
; put a from store into register
; a+2
; value of a+2
; value of variable a
; address of ctrl string
; Call C function
; pop stack 3 push times 4 bytes
; takedown stack frame
; same as "leave" op
; normal, no error, return value
; return