how do you flush the keyboard after input?

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MajorDill

Joined: 01 Nov 2010
Posts: 22

MajorDill 15 Feb 2015, 21:10

So here is some code to get input from the keyboard. It works okay until you enter more
characters than it is expecting (in this case 10). The program exits to linux and any extra input is place after the prompt with the ENTER key. Is there some way to flush out the extra stuff after grabbing the 10?

Code:

format ELF executable

entry _start
  prompt     db  '>'
  in_str     rb  10

_start:
   mov   eax,4           ;display prompt
   mov   ebx,1
   mov   ecx,prompt
   mov   edx,1
   int   0x80

   mov   eax,3           ;get input from keyboard
   mov   ebx,0
   mov   ecx,in_str
   mov   edx,10
   int   0x80

   mov   eax,4           ;display input
   mov   ebx,1
   mov   ecx,in_str
   mov   edx,10
   int   0x80

   mov   eax,1           ;exit linux
   xor   ebx,ebx
   int   0x80

15 Feb 2015, 21:10

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
Location: Unknown

HaHaAnonymous 15 Feb 2015, 21:25

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 17:55; edited 1 time in total

15 Feb 2015, 21:25

gens

Joined: 18 Feb 2013
Posts: 161

gens 15 Feb 2015, 22:56

i don't know of a direct way, so

eax returns the number of bytes read, so just read until you get less then you asked for

15 Feb 2015, 22:56

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
Location: Unknown

HaHaAnonymous 16 Feb 2015, 02:17

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 17:55; edited 2 times in total

16 Feb 2015, 02:17

gens

Joined: 18 Feb 2013
Posts: 161

gens 16 Feb 2015, 12:48

HaHaAnonymous wrote:

Quote:

eax returns the number of bytes read, so just read until you get less then you asked for

The same thing will happen if it what was returned exceeded the buffer size. I think he should increase the size of the buffer for that.

if you request 10 bytes and there is 100 in the stdin buffer, you will get 10 bytes and a 10 in eax

16 Feb 2015, 12:48

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
Location: Unknown

HaHaAnonymous 16 Feb 2015, 23:08

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 17:55; edited 1 time in total

16 Feb 2015, 23:08

Gunner

Joined: 28 Jul 2003
Posts: 17
Location: In my head

Gunner 17 Feb 2015, 00:57

Here is a tutorial on how to deal with this, it is with NASM but easy enough to convert www.dreamincode.net/forums/topic/286248-nasm-linux-terminal-inputoutput-wint-80h/

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17 Feb 2015, 00:57

system error

Joined: 01 Sep 2013
Posts: 670

system error 17 Feb 2015, 07:02

I am not sure if this is related, but EOL character eats up 1 byte from the total. For a reserved 10 chars, only 9 bytes are good. The other 1 is goes to EOL (0ah, enter key). I always reserve one byte for EOL.

17 Feb 2015, 07:02

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