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Misha06



Joined: 18 May 2009
Posts: 8
Misha06
Hello,

I am trying to make a simple window with a dynamic text field, an input field, and a button to initialize a long arithmetic computation.

Could somebody point me to a source where I could find a reference to the API functions I will need...

Also, I'm wonder what is the basic structure of a Win32 FASM program - is there some sort of Window class I need to initialize before I begin?

I am familiar with C# and Java.


Last edited by Misha06 on 19 May 2009, 00:31; edited 1 time in total
Post 18 May 2009, 18:28
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pelaillo
Missing in inaction


Joined: 19 Jun 2003
Posts: 878
Location: Colombia
pelaillo
Please look at the MINIPAD example in fasm download. It has everything you need except the arithmetic computation. The menu will do the same work as the button you want (the button could be added later).

The structure of the example is what a win32 fasm program should look like.
Post 18 May 2009, 22:01
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Misha06



Joined: 18 May 2009
Posts: 8
Misha06
Thank you for your help,

I was wondering about this piece of code:
Code:
Include '%fasminc%/win32ax.inc'
.data
msgBoxCaption db 'Caption',0
value         db 65
NumberOfLoops db 10
.code 
        start:
                mov eax,value
                mov ecx,NumberOfLoops
                CodeToSpin:
                         invoke  MessageBox, NULL, eax, msgBoxCaption, MB_OK
                Loop CodeToSpin
                invoke  ExitProcess,0
       .end start
    



I am expecting the program to count by decrements of 1, displaying the letter "K" - The first letter displays but then the program crashes. What am I doing wrong?
Post 19 May 2009, 00:26
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
Quote:

What am I doing wrong?

Several error here, one is that you moved to ecx the address of NumberOfLoops rather than its actual content (ten). Since the size of the variable is a byte and ECX is a dword (i.e., four bytes), you have to use "movzx ecx, [NumberOfLoops]" (note the square brackets).

But then, a second problem arises, you are using a register considered volatile for the stdcall calling convention, this is, its contents may be destroyed (you have to always assume this will happen not matter whether a particular API function preserves it or not), along with EAX and EDX after a function call.

So, to solve this problem you have to either, use another register (e.g., ESI, EBX or EDI) and replace the loop instruction with "dec reg/jnz CodeToSpin" (reg is the one you have selected), or you can use "push ecx" before calling MessageBox and "pop ecx" immediately after the function call.

And the last problem is that you are passing to MessageBox the address of a byte value. Note that in Assembly none of the data types descend from Object so this means there is no ToString() method binded to them which also means that MessageBox will not receive the expected null-terminated string. So, value declaration should be "value db 75, 0" or "value db 'K', 0". Then on the MessageBox call you need to use a different register than EAX because it is volatile and hence not preserved after MessageBox call (or just pass the address of the variable).

Check if this is what you are expecting:
Code:
Include '%fasminc%/win32ax.inc' 
.data
msgBoxCaption db 'Caption',0

value         db 75, 0 ; It was working before but just by coincidence (the 10 below is "\n" and what comes later is garbage that probably was zero when you executed the program).
NumberOfLoops db 10

.code
        start:
                movzx ecx, [NumberOfLoops]
                CodeToSpin:
                         push    ecx
                         invoke  MessageBox, NULL, value, msgBoxCaption, MB_OK
                         pop     ecx
                Loop CodeToSpin
                invoke  ExitProcess,0
       .end start    
Post 19 May 2009, 02:33
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Misha06



Joined: 18 May 2009
Posts: 8
Misha06
This is exactly what I was looking for, thank you very much - for now my problems are solved.
Post 19 May 2009, 03:12
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Madis731



Joined: 25 Sep 2003
Posts: 2140
Location: Estonia
Madis731
This reminds me that we don't have a "coming from HLL"-section that describes:
Code:
                C & related     ASM & related
                =============== ================
address:        &memory         memory
content:        memory          [memory]

byte:           char            db (define byte)
two bytes:      short int       dw (..word)
four bytes:     int             dd (..dword)
eigth bytes:    longlong        dq (..qword)
    

etc. Smile
Post 19 May 2009, 05:18
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bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
Also this for pointers and dereferencing them...
Code:
               C & related     ASM & related 
               =============== ================ 
pointer:        memory         memory 
derefed:       *memory         [memory]
    

_________________
Coding a 3D game engine with fasm is like trying to eat an elephant,
you just have to keep focused and take it one 'byte' at a time.
Post 19 May 2009, 17:14
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17348
Location: In your JS exploiting you and your system
revolution
So does "*&" give me the value of a variable?
Code:
int a, b;
a=0;
b=4;
a += *&b;    
Post 19 May 2009, 17:18
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bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
NonSyntaxically, yes.

a += *(int*)&b;

asm is so much easier than C/C++ for doing this stuff...
Post 19 May 2009, 17:26
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17348
Location: In your JS exploiting you and your system
revolution
So b loses it's int type when the & is put there?
Post 19 May 2009, 17:29
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bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
The type cast is required for pointer to know its size (type)

_________________
Coding a 3D game engine with fasm is like trying to eat an elephant,
you just have to keep focused and take it one 'byte' at a time.
Post 19 May 2009, 17:34
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17348
Location: In your JS exploiting you and your system
revolution
But b is already an int.
Post 19 May 2009, 18:04
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manfred



Joined: 28 Feb 2009
Posts: 43
Location: Racibórz, Poland
manfred
* and & have same priority and associativity (associa... whatever), so, regardless of variable's type, *&foo returns foo... But I'm not sure.

_________________
Sorry for my English...
Post 19 May 2009, 19:21
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Borsuc



Joined: 29 Dec 2005
Posts: 2466
Location: Bucharest, Romania
Borsuc
revolution wrote:
So does "*&" give me the value of a variable?
why do you ask? is it illogical to you? Confused

_________________
Previously known as The_Grey_Beast
Post 20 May 2009, 00:55
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17348
Location: In your JS exploiting you and your system
revolution
Just trying to understand a little more about it. C has always been an enigma with me.
Post 20 May 2009, 01:32
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LocoDelAssembly
Your code has a bug


Joined: 06 May 2005
Posts: 4633
Location: Argentina
LocoDelAssembly
However, I must say that bitshifter's table may not be really accurate. If we suppose for a moment that "memory" is of type "int *", then I would construct the table this way:

Code:
               C & related     ASM & related 
               =============== ================ 
reference:      &memory        memory
pointer:        memory         [memory] 
derefed:       *memory         reg <- [memory] / [reg] ([[memory]] if double indirection were supported)     
Post 20 May 2009, 02:13
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17348
Location: In your JS exploiting you and your system
revolution
So in my example above, does b lose it's int type when the & is put there?
Post 20 May 2009, 02:19
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bitshifter



Joined: 04 Dec 2007
Posts: 764
Location: Massachusetts, USA
bitshifter
No, for instance these retain their type without need of type casting...

int a = 0;
int *b = &a;
int *c = b;
int d = *c;

_________________
Coding a 3D game engine with fasm is like trying to eat an elephant,
you just have to keep focused and take it one 'byte' at a time.
Post 20 May 2009, 06:22
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