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CS 456 - Systems Programming
Spring 2024
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Displaying ./code/apr10/crawler.asm
; Crawler
; Compile with: nasm -f elf crawler.asm
; Link with (64 bit systems require elf_i386 option): ld -m elf_i386 crawler.o -o crawler
; Run with: ./crawler
%include 'functions.asm'
SECTION .data
; our request string
request db 'GET / HTTP/1.1', 0Dh, 0Ah, 'Host: 139.162.39.66:80', 0Dh, 0Ah, 0Dh, 0Ah, 0h
SECTION .bss
buffer resb 1, ; variable to store response
SECTION .text
global _start
_start:
xor eax, eax ; init eax 0
xor ebx, ebx ; init ebx 0
xor edi, edi ; init edi 0
_socket:
push byte 6 ; push 6 onto the stack (IPPROTO_TCP)
push byte 1 ; push 1 onto the stack (SOCK_STREAM)
push byte 2 ; push 2 onto the stack (PF_INET)
mov ecx, esp ; move address of arguments into ecx
mov ebx, 1 ; invoke subroutine SOCKET (1)
mov eax, 102 ; invoke SYS_SOCKETCALL (kernel opcode 102)
int 80h ; call the kernel
_connect:
mov edi, eax ; move return value of SYS_SOCKETCALL into edi (file descriptor for new socket, or -1 on error)
push dword 0x4227a28b ; push 139.162.39.66 onto the stack IP ADDRESS (reverse byte order)
push word 0x5000 ; push 80 onto stack PORT (reverse byte order)
push word 2 ; push 2 dec onto stack AF_INET
mov ecx, esp ; move address of stack pointer into ecx
push byte 16 ; push 16 dec onto stack (arguments length)
push ecx ; push the address of arguments onto stack
push edi ; push the file descriptor onto stack
mov ecx, esp ; move address of arguments into ecx
mov ebx, 3 ; invoke subroutine CONNECT (3)
mov eax, 102 ; invoke SYS_SOCKETCALL (kernel opcode 102)
int 80h ; call the kernel
_write:
mov edx, 43 ; move 43 dec into edx (length in bytes to write)
mov ecx, request ; move address of our request variable into ecx
mov ebx, edi ; move file descriptor into ebx (created socket file descriptor)
mov eax, 4 ; invoke SYS_WRITE (kernel opcode 4)
int 80h ; call the kernel
_read:
mov edx, 1 ; number of bytes to read (we will read 1 byte at a time)
mov ecx, buffer ; move the memory address of our buffer variable into ecx
mov ebx, edi ; move edi into ebx (created socket file descriptor)
mov eax, 3 ; invoke SYS_READ (kernel opcode 3)
int 80h ; call the kernel
cmp eax, 0 ; if return value of SYS_READ in eax is zero, we have reached the end of the file
jz _close ; jmp to _close if we have reached the end of the file (zero flag set)
mov eax, buffer ; move the memory address of our buffer variable into eax for printing
call sprint ; call our string printing function
jmp _read ; jmp to _read
_close:
mov ebx, edi ; move edi into ebx (connected socket file descriptor)
mov eax, 6 ; invoke SYS_CLOSE (kernel opcode 6)
int 80h ; call the kernel
_exit:
call quit ; call our quit function
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