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global _start
section .text
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
mov rdx, rax
mov rax, 1
mov rdi, 1
mov rsi, buf
syscall
mov rax, rbx
jmp process_fd
.ret:
; return rax
mov rax, rbx
ret
_start:
; r12 = argc
mov rbp, rsp
; r14 = argv0
mov r14, [rsp+8]
mov r12, [rbp]
cmp r12, 2
jl final.stdin
; r13 = our flag holder
xor r13, r13
add rbp, 8 * 2
; flag consumer loop
.loop:
cmp r12, 2
jl final
mov r11, [rbp]
mov r11, [r11]
and r11, 0xff
cmp r11, "-"
jne .cont
; solid - is stdin
; shouldnt be consumed
mov r11, [rbp]
add r11, 1
mov r11, [r11]
and r11, 0xff
cmp r11, 0x00
je .cont
mov r11, [rbp]
xor r9, r9
mov [rbp], r9 ; consume argument (should be ignored in final loop)
; inner loop to process all flags
.inloop:
inc r11
mov r10, [r11]
and r10, 0xff
cmp r10, 0x00
je .cont
; basically switch() { case }
cmp r10, "u"
je .inloop
jmp usage
.cont:
add rbp, 8
sub r12, 1
jmp .loop
; actual FD processor loop
final:
; check for actual arguments
mov rbp, rsp
mov r12, [rbp]
add rbp, 8 * 2
xor rdx, rdx
.loop2:
cmp r12, 2
jl .cont2
add rdx, [rbp]
add rbp, 8
sub r12, 1
jmp .loop2
.cont2:
cmp rdx, 1
jl .sstdin
; fix rbp and r12
mov rbp, rsp
mov r12, [rbp]
add rbp, 8 * 2 ; jump past 1st arg
.loop:
; if no more entries; exit
cmp r12, 2
jl exit
mov r10, [rbp]
cmp r10, 1
jl .cont
; at this point, all arguments starting with -
; should only be -\0 (stdin)
; (we can be lazy and skip checking)
mov r11, [rbp]
mov r11, [r11]
and r11, 0xff
cmp r11, "-"
je .stdin
; 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
.cont:
add rbp, 8
sub r12, 1
jmp .loop
.sstdin:
mov r12, 1
.stdin:
mov rax, 0
call process_fd
jmp .cont
usage:
;usage w/ argv0
mov rax, usagep1
call pstring
mov rax, r14
call pstring
mov rax, usagep2
call pstring
jmp errorexit
error:
;exit(1)
; TODO: process RAX to print meaningful message
mov rax, errormsg
call pstring
errorexit:
mov rax, 60
mov rdi, 1
syscall
; function to print null terminated string
; arg: rax is pointer
pstring:
; r8 is length
; r9 is a cached buffer for operations
xor r8, r8
mov r9, rax
.loop:
mov r10, [r9]
and r10, 0xff
cmp r10, 0x00
je .fin
inc r8
inc r9
jmp .loop
.fin:
; print to stderr
mov rdx, r8
mov rsi, rax
mov rdi, 2
mov rax, 1
syscall
ret
exit:
;exit(0)
mov rax, 60
mov rdi, 0
syscall
section .data
usagep1: db "Usage: ", 00
usagep2: db " [-u] [file ...]", 10, 00
errormsg: db "An error has occured! Unfortunately, this program isnt complex enough to display the error yet. Try using strace!", 10, 00
section .bss
smallbuf: resb 8
bufSize: equ 65536
buf: resb bufSize
|
