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first assembly program
Posted: Wed Mar 28, 2007 7:38 pm
by baileydr
So this is my first program; I'm trying to get comfortable with it, so instead of copying assembly from the wiki, I can actually do it.
So, help I'm looking for:
1. Style: I feel as if I'm going about control wrong
2. Fix the segfault; if not, point me to my error
3. everything else. I need all the help I can get.
BTW, don't ask why put_char is in put_integer.asm
I could use printf, but that would defeat the purpose of the work, wouldn't it?
Posted: Thu Mar 29, 2007 1:33 pm
by baileydr
oh yea, There's a bug in it too. It puts the negative sign after the number; easily fixable.
All I'm really looking for is a pointer in the right direction...
[edit]Oh, and in response to a message, this just prints a message. It divides the number by ten, grabs the integer, and pushes it onto the stack so it prints in the right order.[/edit]
Posted: Thu Mar 29, 2007 6:49 pm
by baileydr
ok, I fixed it... I'm still a bit unsure about my conditional jumps, or if I'm doing it well or anything. So suggestions are still welcome....
Posted: Mon Apr 02, 2007 11:07 am
by ~
Code: Select all
;;linux_io.inc.fakefilename.asm
extern put_integer
%macro print_string 0
mov eax, 4
mov ebx, 1
int 80h
%endmacro
Code: Select all
;;put_integer.asm
segment .data
ascii_offset db '0123456789ABCDEF' ; our offset for everything from b
segment .bss
Pi_sign resb 1
segment .text
global put_integer
global print_stack
global put_char
put_char:
push ebp ; set up the stack
mov ebp, esp
push eax ; store the registers
push ebx
push ecx
push edx
mov ecx, eax ; it's nice to use eax for the argument for this 'function'
mov eax, 4 ; write
mov ebx, 1 ; stdout
mov edx, 1 ; one byte
pop edx ; restore the registers
pop ecx
pop ebx
pop eax
pop ebp ; and the base pointer
ret
put_integer:
push ebp
mov esp, ebp
push eax ; save the registers on the stack
push ebx
push ecx
push edx
mov ecx, 1 ; the digit counter
js __pi_signed
__pi_integer_loop:
xor edx, edx ; clear edx
mov ebx, 10 ; the 'digit offset'
div ebx ; eax/ebx or eax/10
add edx, ascii_offset ; convert it to the ascii digit
push edx ; store the remainder for printing
cmp eax, 0 ; if the quotient is zero, we've reached the end.
jge __pi_print_stack ; so we print out the stack
add ecx, 1 ; incriment the digit loops
jmp __pi_integer_loop ; recursive
__pi_print_stack:
dec ecx
pop eax ; pop the variables into the stack
call put_char
cmp ecx, 0
jle __pi_print_stack ; If we've reached the last digit, we're done
cmp byte [Pi_sign], 0x8
je __pi_hyphen
__pi_return:
pop edx
pop ecx
pop ebx
pop eax
pop ebp
ret
__pi_signed:
;; if it's signed, then we check whether it's negative or not.
;; if it is, then we push a hyphen in front of it.
cmp eax, 0
jl __pi_negative
mov byte [Pi_sign], 0
sal eax, 1
jmp __pi_integer_loop
__pi_negative:
mov byte [Pi_sign], 0x8
sal eax, 1
jmp __pi_integer_loop ; jump back in!
__pi_hyphen:
mov eax, 45
call put_char
jmp __pi_return
Why did you named it "linux_io.inc.fakefilename.asm"?
"Fake File Name"
Posted: Mon Apr 02, 2007 12:42 pm
by Combuster
because the forum settings don't allow files with .inc extension