;name: keyfilter.asm
;
;description: The program displays the ASCII code in hexadecimal of the pressed key.
;
;
;build: nasm -felf64 keyfilter.asm -o keyfilter.o
; ld -melf_x86_64 keyfilter.o -o keyfilter
;
;remark: On terminals with escape key sequences binded to keys (like the cursor keys) the
; program exits after pressing those (since ESCAPE sequences starts with the ESC key)
;
;source: 11.7 Writing UNIX® Filters - FreeBSD Developers’ Handbook
bits 64
%include "unistd.inc"
%include "sys/termios.inc"
section .bss
buffer: resq 8
.length: equ $-buffer
section .rodata
intro: db "filter - by Agguro 2011 source: FreeBSD Developers’ Handbook.", 10
db "The program shows the ASCII codes of the pressed keys. ESC terminates the "
db "program with key code or CTRL-C without.", 10
db "start typing >> "
.length: equ $-intro
EOL:
.start: db "1B", 10 ;print the ASCII code for ESC to be complete
.end:
section .data
output: db 0,0," "
.length: equ $-output
TERMIOS termios ;termios structure
section .text
global _start
_start:
mov rsi,intro
mov rdx,intro.length
call Write
call termios_canonical_mode_off ;switch canonical mode off
call termios_echo_mode_off ;no echo
getKeyStroke:
syscall read,stdin,buffer,buffer.length
cmp byte[buffer],0x1B ;if ESC pressed
je Exit
mov al,byte[buffer]
toASCII:
shl rax,4 ;most significant nibble in AH
shr al,4 ;least significant nibble in AL
or ax,3030h ;attempt to convert both to ASCII
cmp al,"9" ;is AL = ascii 9 ?
jle .highNibble
add al,7
.highNibble:
cmp ah,"9"
jle .done
add ah,7
.done:
ror ax,8 ;little ENDIAN notation
mov word[output],ax ;ASCII in buffer to print
mov rsi,output
mov rdx,output.length
call Write
jmp getKeyStroke
Exit:
mov rsi,EOL
mov rdx,EOL.end-EOL.start
call Write
call termios_canonical_mode_on ;switch canonical mode back on
call termios_echo_mode_on ;restore echo
syscall exit,0
;write to STDOUT
Write:
push rcx
push rax
push rdi
syscall write,stdout
pop rdi
pop rax
pop rcx
ret
;subroutine to switch canonical mode on
;RAX is unchanged on exit
termios_canonical_mode_on:
push rax
mov rax,ICANON
jmp termios_set_localmode_flag
;subroutine to switch echo mode on
;RAX is unchanged on exit
termios_echo_mode_on:
push rax
mov rax,ECHO
jmp termios_set_localmode_flag
;subroutine to set the bits in the c_lflag stored in EAX
;RAX is unchanged on exit
termios_set_localmode_flag:
push rax
call termios_stdin_read
or dword[termios.c_lflag],eax
call termios_stdin_write
pop rax
pop rax
ret
;subroutine to switch canonical mode off
;RAX is unchanged on exit
termios_canonical_mode_off:
push rax
mov rax,ICANON
jmp termios_clear_localmode_flag
;subroutine to switch echo mode off
;RAX is unchanged on exit
termios_echo_mode_off:
push rax
mov rax,ECHO
jmp termios_clear_localmode_flag
;subroutine to clear the bits in the c_lflag stored in EAX
;RAX is unchanged on exit
termios_clear_localmode_flag:
push rax
call termios_stdin_read
not eax
and [termios.c_lflag],eax
call termios_stdin_write
pop rax
pop rax
ret
;subroutine for all TCGETS operation on the syscall IOCTL
;the original value of RCX is restored on exit
termios_stdin_read:
push rsi
mov rsi,TCGETS
jmp termios_stdin_syscall
;subroutine for all TCSETS operation on the syscall IOCTL
;the original value of RCX is restored on exit
termios_stdin_write:
push rsi
mov rsi,TCSETS
jmp termios_stdin_syscall
;subroutine for operations on the syscall IOCTL for STDIN
;all registers are restored to their original values on exit of the subroutine
termios_stdin_syscall:
push rax
push rdi
push rdx
mov rdx,termios
syscall ioctl,stdin
pop rdx
pop rdi
pop rax
pop rsi
ret
