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Index > Linux > Unbuffered input with ioctl, termios not working

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z33ky



Joined: 24 May 2010
Posts: 5
Location: Germany
z33ky
Hello there. I'm new to FASM and new around here Smile
I learned an assembler in school, for the myAVR micro-controller, and I thought it'd be fun to learn an assembly language for the average desktop computer.

I've completed a small tutorial and read some parts of the FASM manual, but I can't get my head around this problem:
I'm trying to get unbuffered input from stdin (without a library) and apparently the ioctl syscall should be working for this, but it just breaks the terminals stdin.
Here's the assembly I am using:
Code:
format elf executable

entry main

;syscalls
SYSCALL_EXIT    equ 1
SYSCALL_READ    equ 3
SYSCALL_IOCTL   equ 54

;standard I/O
STDIN   equ 0

;ioctl subfunctions
TCGETS  equ 0x5401
TCSETS  equ 0x5402

;struct termios
struc termios{
        .c_iflag rd 1 ;input mode flags
        .c_oflag rd 1 ;output mode flags
        .c_cflag rd 1 ;control mode flags
        .c_lflag rd 1 ;local mode flags
        .c_line rb 1 ;line discipline
        .c_cc rb 32 ;control characters
        .c_ispeed rd 1 ;input speed
        .c_ospeed rd 1 ;output speed
}

;termios flags
ICANON equ 2 ;Do erase and kill processing
ECHO equ 8 ;Enable echo

;static data
segment readable writeable

oldtermios termios
newtermios termios

;--------
segment executable
main:
        ;get old termios mode
        mov eax, SYSCALL_IOCTL
        mov ebx, STDIN
        mov ecx, TCGETS
        mov edx, oldtermios

        ;copy termios
;       mov esi, oldtermios
;       mov edi, newtermios
;       mov ecx, 14
;       repz movs dword [edi], [esi]
;       repz movs byte [edi], [esi]

        ;set new termios
;       and dword [newtermios.c_lflag], not (ICANON or ECHO)
        mov eax, SYSCALL_IOCTL
        mov ebx, STDIN
        mov ecx, TCSETS
        mov edx, oldtermios ;newtermios
        int 0x80

        ;get input
        mov eax, SYSCALL_READ
        mov ebx, STDIN
        mov ecx, esp
        mov edx, 1
        int 0x80

        ;reset termios
        mov eax, SYSCALL_IOCTL
        mov ebx, STDIN
        mov ecx, TCSETS
        mov edx, oldtermios
;       int 0x80

        ;exit
        mov eax, SYSCALL_EXIT
        mov ebx, 0
        int 0x80    

I am actually just getting the current terminal settings and set them again without modification; In the commented code you can see my intention after I get that working.

Upon executing the program it immediately closes without waiting for input and I cannot input anything further in the terminal.

Here's the struct as in /usr/include/bits/termios.h
Code:
typedef unsigned char   cc_t;
typedef unsigned int    speed_t;
typedef unsigned int    tcflag_t;

#define NCCS 32
struct termios
  {
    tcflag_t c_iflag;           /* input mode flags */
    tcflag_t c_oflag;           /* output mode flags */
    tcflag_t c_cflag;           /* control mode flags */
    tcflag_t c_lflag;           /* local mode flags */
    cc_t c_line;                        /* line discipline */
    cc_t c_cc[NCCS];            /* control characters */
    speed_t c_ispeed;           /* input speed */
    speed_t c_ospeed;           /* output speed */
#define _HAVE_STRUCT_TERMIOS_C_ISPEED 1
#define _HAVE_STRUCT_TERMIOS_C_OSPEED 1
  };    
Post 24 May 2010, 12:31
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z33ky



Joined: 24 May 2010
Posts: 5
Location: Germany
z33ky
Alright, fixed.
I was missing an int 0x80 after the first SYSCALL_IOCTL :X
Post 24 May 2010, 21:09
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