Thank you for taking the time to look at my question and all help is appreciated. I will keep this question simple, so here it is:
; Program Author: David Mark Serrano
; Program Name: Battle_Chess
; Date Created: July 12, 2023
; Version: 1.0
; Purpose: To render a textual chessboard on the Linux Terminal for a game of chess against an AI opponent
; Built using file "makefile":
;
; Battle_Chess: Board_Render.o Battle_Chess.o
; ld -m elf_i386 -o Battle_Chess Battle_Chess.o Board_Render.o
;
; Board_Render.o: Board_Render.asm
; nasm -f elf32 -g -o Board_Render.o Board_Render.asm
;
; Battle_Chess.o: Battle_Chess.asm
; nasm -f elf32 -g -o Battle_Chess.o Battle_Chess.asm
section .data ; Section for initialized data
; Buffer for 'GWINSZ' procedure
winsize_struct db 32
GWINSZ:
mov eax, 54 ; Specify `ioctl` syscall in 32-bit x86 assembly
mov ebx, 1 ; Stdin stored in ebx
mov ecx, 0x5413 ; 'ioctl' code for getting Terminal size
mov edx, winsize_struct ; Address of `winsize_struct` buffer is stored in `edx`
int 0x80 ; Syscall 128 / Vector Interrupt 128 (Kernel Services Dispatcher/Syscall Dispatcher)
ret ; Return from procedure
section .text
global _start
_start:
call GWINSZ ; Call 'GWINSZ' procedure defined above
mov eax, 4 ; Specify 'sys_write' syscall in 32-bit x86 assembly language
mov ebx, 1 ; STDOUT file descriptor stored in register 'ebx'
mov ecx, winsize_struct ; winsize_struct buffer address stored in register 'ecx'
mov edx, 32 ; Length of winsize_struct buffer in bytes
int 0x80 ; Vector Interrupt 128 (Kernel Services/Syscall Dispatcher)
; This group of instructions (Line 97 - Line 97) will terminate the program and return code '0' to Linux to signal proper execution
mov eax, 0x1 ; Specify sys_exit syscall
xor ebx, ebx ; Clear `ebx` register so that it returns exit code 0
int 0x80 ; Specify Vector Interrupt 128 (Kernel Services/Syscall Dispatcher)
This is the code that I wrote on my 2011 MacBook Air running Ubuntu 20.04.5 LTS (I know it's ancient). I am simply learning to write 32-bit x86 assembly using NASM (Intel syntax) and I'm working on my first project. My question is simple: Why can't the buffer 'winsize_struct' be printed? I want to retrieve the size of the Terminal and store that size in 'winsize_struct', and then print it out to the screen using the standard 'sys_write' syscall. I'm doing this because part of my project requires ensuring the terminal is opened up to a minimum size, and if it isn't then I will terminate the project prematurely with an error message informing the end-user to increase the Terminal to the minimum dimensions of $LINES and $COLUMNS. I am new to x86 assembly, please be nice and as helpful as you can because I have already tried many things to no avail.
Thank you for your help in advance.
I have already tried various things, but to no avail.
1.) I experimented with the 'GWINSZ' procedure, I changed the instruction 'mov edx, winsize_struct' to 'lea edx, [winsize_struct]'. This did not work and nothing is printed to the screen. 2.) I experimented with different methods for calling 'ioctl' in the 'GWINSZ' procedure. I settled for value 54 to be stored in register 'eax' since this is the syscall number for 'ioctl', I settled and 0x5413 as the TIOCGWINSZ code stored in register 'ecx'. 3.) I experimented with writing the 'winsize_struct' buffer in the 'section .bss' part of the program. There was no effect at all. 4.) I experimented with the value of register 'ebx' in the 'GWINSZ' procedure. I sometimes tried 0 or 1, but nothing seemed to be work.
I still do not know why there seems to be nothing stored in the buffer despite the apparent success in the syscall! How can I get the values $LINES and $COLUMNS to be printed?
