Im currently working on a compiler and Ive just gotten throught with a few control statements, subs/functions and all that good stuff and Im starting to work on basic I/O (print, input, locate, color, cls) and I thought print was finished but there seems to be a bug in it.
Here is the source for a little demo that shows the bug.
main{
int count;
label loop;
if(count>100){goto endit;};
print(count);
count=count+1;
goto loop;
label endit;
end;
}
Here is the assembler code
.486
.model flat, stdcall
option casemap :none
include windows.inc
include user32.inc
include kernel32.inc
include gdi32.inc
include C:\masm32\macros\macros.asm
include masm32.inc
includelib gdi32.lib
includelib user32.lib
includelib kernel32.lib
includelib masm32.lib
.data?
ConsoleOut dd ?
ConsoleIn dd ?
printstr db ?
.code
start:
invoke GetStdHandle,STD_OUTPUT_HANDLE
mov ConsoleOut,eax
invoke GetStdHandle,STD_INPUT_HANDLE
mov ConsoleIn,eax
;int
;label
lblloop:
;if
MOV eax, varcount
push eax
MOV eax,100
mov ebx,eax
pop eax
cmp eax,ebx
jb KCLBL1
;goto
jmp lblendit
KCLBL1:
;print
MOV eax, varcount
invoke wsprintf,addr printstr,CTXT('%u'),eax
invoke WriteFile,ConsoleOut,addr printstr,len(addr printstr),NULL,NULL
;count
MOV eax, varcount
PUSH eax
MOV eax,1
POP ebx
ADD eax,ebx
MOV varcount,eax
;goto
jmp lblloop
;label
lblendit:
;end
invoke ExitProcess,0
.data?
varcount dd ?
end start
As you can see if you test it, it doesnt work. It stay looping on 1. I believe the problem is with Wsprintf but I dont know how to fix it.
Help would be greatly appreciated, thanks.
Questions about code generation should be in the assembler/compiler technology forum.
But the problem is basic data allocation - you're only allocating ONE byte for the printstr buffer. wsprintf will overwrite any data that follows printstr. Whatever follows printstr (I see that an unaligned varcount follows printstr) will get overwritten.
KcDan,
You only allocated a single byte for printstr, you need more than that. :bg
Oops, tenkey posted while I was writing this.
Bah! Thanks for the help, it now works correctly.
printstr db 1024 dup (0)