111 lines
3.2 KiB
NASM
111 lines
3.2 KiB
NASM
extern NR_read
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extern NR_write
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extern NR_open
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extern NR_close
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extern strlen
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section .rodata
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O_RDONLY equ 00000000q
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O_WRONLY equ 00000001q
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O_RDWR equ 00000002q
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O_CREAT equ 00000100q
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O_TRUNC equ 00001000q
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O_APPEND equ 00002000q
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section .text
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global fopen
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global fclose
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global fwrite
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;----- fopen(const char *filename, const char *mode) -----;
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; return value: pointer to file or NULL if file failed to open
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; ┌─────────────┬───────────────────────────────┐
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; │fopen() mode │ open() flags │
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; ├─────────────┼───────────────────────────────┤
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; │ r │ O_RDONLY │
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; ├─────────────┼───────────────────────────────┤
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; │ w │ O_WRONLY | O_CREAT | O_TRUNC │
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; ├─────────────┼───────────────────────────────┤
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; │ a │ O_WRONLY | O_CREAT | O_APPEND │
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; ├─────────────┼───────────────────────────────┤
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; │ R │ O_RDWR │
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; ├─────────────┼───────────────────────────────┤
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; │ W │ O_RDWR | O_CREAT | O_TRUNC │
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; ├─────────────┼───────────────────────────────┤
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; │ A │ O_RDWR | O_CREAT | O_APPEND │
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; └─────────────┴───────────────────────────────┘
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fopen:
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push rbp
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mov rbp, rsp
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cmp byte [rsi], 'r'
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je .setMode_r
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cmp byte [rsi], 'w'
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je .setMode_w
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cmp byte [rsi], 'a'
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je .setMode_a
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cmp byte [rsi], 'R'
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je .setMode_R
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cmp byte [rsi], 'W'
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je .setMode_W
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cmp byte [rsi], 'A'
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je .setMode_A
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xor rax, rax
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jmp .quit
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.setMode_r:
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mov rsi, O_RDONLY
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jmp .open
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.setMode_w:
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mov rsi, O_WRONLY | O_CREAT | O_TRUNC
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jmp .open
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.setMode_a:
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mov rsi, O_WRONLY | O_CREAT | O_APPEND
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jmp .open
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.setMode_R:
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mov rsi, O_RDWR
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jmp .open
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.setMode_W:
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mov rsi, O_RDWR | O_CREAT | O_TRUNC
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jmp .open
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.setMode_A:
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mov rsi, O_RDWR | O_CREAT | O_APPEND
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jmp .open
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.open:
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mov rax, NR_open
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syscall
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.quit:
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leave
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ret
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;----- fclose(FILE* fp) -----;
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; return value: 0 on success, below 0 otherwise
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fclose:
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push rbp
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mov rbp, rsp
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mov rax, NR_close
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syscall
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leave
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ret
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;----- fwrite(FILE* fp, char* str) -----;
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; writes a string to opened file
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; return value: 0 on success, below 0 otherwise
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fwrite:
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push rbp
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mov rbp, rsp
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mov r9, rdi
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mov rdi, rsi
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call strlen
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mov rdx, rax
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mov rax, NR_write
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mov rdi, r9
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syscall
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leave
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ret
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