123 lines
2.8 KiB
NASM
123 lines
2.8 KiB
NASM
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; hello_mmap.asm
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%define O_RDONLY 0
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%define PROT_READ 0x1
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%define MAP_PRIVATE 0x2
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%define SYS_WRITE 1
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%define SYS_OPEN 2
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%define SYS_CLOSE 3
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%define SYS_FSTAT 5
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%define SYS_MMAP 9
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%define SYS_MUNMAP 11
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%define SYS_EXIT 60
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%define FD_STDOUT 1
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%define FSTAT_SIZE 144
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%define FSTAT_FSIZE_OFFSET 48
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global print_file
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global print_string
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section .data
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fstat_buff: db "hello", 0
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section .text
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; use exit system call to shut down correctly
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exit:
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mov rax, SYS_EXIT
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xor rdi, rdi
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syscall
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; These functions are used to print a null terminated string
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; rdi holds a string pointer
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print_string:
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push rdi
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call string_length
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pop rsi
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mov rdx, rax
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mov rax, SYS_WRITE
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mov rdi, FD_STDOUT
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syscall
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ret
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string_length:
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xor rax, rax
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.loop:
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cmp byte [rdi+rax], 0
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je .end
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inc rax
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jmp .loop
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.end:
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ret
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; This function is used to print a substring with given length
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; rdi holds a string pointer
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; rsi holds a substring length
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print_substring:
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mov rdx, rsi
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mov rsi, rdi
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mov rax, SYS_WRITE
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mov rdi, FD_STDOUT
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syscall
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ret
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; rdi - file name
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print_file:
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push r12
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push r13
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; Вызовите open и откройте fname в режиме read only.
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mov rax, SYS_OPEN
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mov rsi, O_RDONLY ; Open file read only
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xor rdx, rdx ; We are not creating a file
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; so this argument has no meaning
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syscall
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; rax holds the opened file descriptor now
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mov r12, rax ; save fd to r12
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; get stat of file
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mov rdi, r12
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mov rsi, fstat_buff
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mov rax, SYS_FSTAT
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syscall
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; get size of file in from its stats
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mov r13, fstat_buff
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add r13, FSTAT_FSIZE_OFFSET
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mov r13, [r13]
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; now rsi stores the files size
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; Вызовите mmap c правильными аргументами
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; Дайте операционной системе самой выбрать, куда отобразить файл
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; Размер области возьмите в размер страницы
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; Область не должна быть общей для нескольких процессов
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; и должна выделяться только для чтения.
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xor rdi, rdi
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mov r8, r12
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xor r9, r9
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mov rsi, r13
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mov rdx, PROT_READ
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mov r10, MAP_PRIVATE
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mov rax, SYS_MMAP
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syscall
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; now rax stores the mapped file address
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; с помощью print_substring теперь можно вывести его содержимое
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push rax ; save mapped file address
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mov rdi, rax
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mov rsi, r13
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call print_substring
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; unmap mapped file
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pop rdi ; retrieve mapped file address from stack
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mov rsi, r13
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mov rax, SYS_MUNMAP
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syscall
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; close file
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mov rdi, r12
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mov rax, SYS_CLOSE
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syscall
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pop r13
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pop r12
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ret
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