chapter 13, problem 3

Author: eliyanovva

fileWrite.asm

@@ -0,0 +1,185 @@
+section .data
+
+; Standard constants
+
+LF equ 10 ; line feed
+NULL equ 0 ; end of string
+TRUE equ 1
+FALSE equ 0
+EXIT_SUCCESS equ 0 ; success code
+STDIN equ 0 ; standard input
+STDOUT equ 1 ; standard output
+STDERR equ 2; standard error
+
+SYS_read equ 0 ; read
+SYS_write equ 1 ; write
+SYS_open equ 2 ; open
+SYS_close equ 3 ; close
+SYS_fork equ 57 ; fork
+SYS_exit equ 60 ; terminate
+SYS_creat equ 85 ; file open/create
+SYS_time equ 201 ; get time
+
+O_CREAT equ 0x40
+O_TRUNC equ 0x200
+O_APPEND equ 0x400
+
+O_RDONLY equ 000000q ; read only
+O_WRONLY equ 000001q ; write only
+O_RDWR equ 000002q ; read and write
+
+S_IRUSR equ 00400q
+S_IWUSR equ 00200q
+S_IXUSR equ 00100q
+
+;--------------------------------------------------
+; Variables which will be used in main
+
+newLine db LF, NULL
+header db LF, "File Write Example.", LF, LF, NULL
+fileName db "./password_storage.txt", NULL
+password db "mamamieeli!123", NULL
+len dq 0
+
+writeDone db "Write Completed", LF, NULL
+fileDesc dq 0
+errMsgOpen db "Error opening file.", LF, NULL
+errMsgWrite db "Error writing to file.", LF, NULL
+
+;--------------------------------------------------
+
+section .text
+global _start
+_start:
+
+; Display header
+
+mov rdi, fileName
+mov rsi, password
+call writeToFile
+
+exit:
+    mov rax, SYS_exit
+    mov rdi, EXIT_SUCCESS
+    syscall
+
+
+writeToFile:
+
+mov r8, rdi ; store address of the file in r8
+mov r9, rsi ; store the password in r9
+
+    push rdi
+    mov rdi, header
+    call printString
+    pop rdi
+
+; Open file
+
+    push rsi
+openInputFile:
+    mov rax, SYS_creat ; file open/create
+    ;mov rdi, fileName ; file name string
+    mov rsi, S_IRUSR | S_IWUSR | S_IXUSR ; allow read and write
+    syscall
+
+    cmp rax, 0 ; check for success
+    jl errorOnOpen
+
+    mov qword[fileDesc], rax ; save descriptor
+
+; Write to file
+    pop rsi
+    push rdi
+    mov rdi, rsi
+    call strLen
+    pop rdi ; get the length of the password in rax
+
+    mov rdx, rax ; set parameters for writing in the file
+    mov rax, SYS_write
+    mov rdi, qword[fileDesc]
+    mov rsi, r9
+    syscall
+
+    cmp rax, 0
+    jl errorOnWrite
+
+    mov rdi, writeDone;
+    call printString
+
+; Close file
+    mov rax, SYS_close
+    mov rdi, qword[fileDesc]
+    syscall
+
+    jmp exampleDone
+
+; Error on open
+errorOnOpen:
+    mov rdi, errMsgOpen
+    call printString
+    jmp exampleDone
+
+; Error on write
+errorOnWrite:
+    mov rdi, errMsgWrite
+    call printString
+    jmp exampleDone
+
+exampleDone:
+    ret
+
+
+; print NULL terminated string
+
+global printString
+printString:
+    push rbp
+    mov rbp, rsp
+    push rbx
+
+; Count chars in string
+
+    mov rbx, rdi
+    mov rdx, 0
+
+strCountLoop:
+    cmp byte[rbx], NULL
+    je strCountDone
+    inc rdx
+    inc rbx
+    jmp strCountLoop
+
+strCountDone:
+    cmp rdx, 0
+    je prtDone
+
+    mov rax, SYS_write
+    mov rsi, rdi
+    mov rdi, STDOUT
+    syscall
+
+    prtDone:
+    pop rbx
+    pop rbp
+    ret
+
+; find the length of a string stored on address in rdi
+strLen:
+    push rbx
+    push rdx
+    mov rbx, rdi
+    mov rdx, 0
+
+CountLoop:
+    cmp byte[rbx], NULL
+    je funcStrLenDone
+    inc rdx
+    inc rbx
+    jmp CountLoop
+
+funcStrLenDone:
+    mov rax, rdx ; store the string length in rax
+    pop rdx
+    pop rbx
+    ret