diff options
| -rw-r--r-- | cat.s | 97 |
1 files changed, 92 insertions, 5 deletions
@@ -1,16 +1,103 @@ global _start section .text -_start: +process_fd: + ; rax = fd + + ; read(rax, buf, bufSize) + mov rbx, rax + mov rdi, rax + mov rsi, buf + mov rdx, bufSize + mov rax, 0 + syscall + + ; check if stuff was read + cmp rax, 1 + jl .ret + + ; write(1, buf, rax) + mov rdi, 1 + mov rsi, buf + mov rdx, rax mov rax, 1 + syscall + + ; continue loop + mov rax, rbx + jmp process_fd +.ret: + ; return rax + mov rax, rbx + ret + +_start: + ; r12 = argc + mov rbp, rsp + mov r12, [rbp] + cmp r12, 2 + jl .stdin + + add rbp, 8 * 2 ; jump past 1st arg + +.loop: + ; if no more entries; exit + cmp r12, 2 + jl exit + + ; arguments starting with "-" are special cases + mov r13, [rbp] + cmp r13, 0x2d ;'-' + je .special + + ; open(rbp, 0, 0) + mov rax, 2 + mov rdi, [rbp] + mov rsi, 0 + mov rdx, 0 + syscall + + ; make sure fd exists + cmp rax, 1 + jl .error + ; print file + call process_fd + ; returns input + ; close(rax) + mov rdi, rax + mov rax, 3 + syscall + + ; prepare registers for next loop + add rbp, 8 + sub r12, 1 + jmp .loop + + ; unreachable. insurance + jmp exit + +.special: + ;special case handler (TODO) + ; stdin passthrough +.stdin: + mov rax, 0 + call process_fd + jmp .loop + +.error: + ;exit(1) + ; TODO: process RAX to print meaningful message + mov rax, 60 mov rdi, 1 - mov rsi, msg - mov rdx, msgSize syscall +exit: + ;exit(0) mov rax, 60 mov rdi, 0 syscall section .data -msg: db "Hello, world!", 10 -msgSize: EQU $ - msg + + section .bss +bufSize: equ 65536 +buf: resb bufSize |