C to Assembly...
With a bit of knowledge comes great power! To be able to look at
assembly and know how it would look in C is a great thing..... for one, it
allows you to see what other people have written in C, without even looking at
there C code...mhahaha.
A great way to explore other peoples compiled code is with some dissasembers,
such as hackman or mdasm ...or even winhex :)
Now Lets take a look at loops... as loops are a sweet way of doing things
over and over again with a relatively few lines of code.... Take a look how much
C simplifies our lives.... but also notice how you could optimise that assembly
if you had your way :)
| Comparison: ForLoop |
|
int b=0;
for( int i=0;
i<10; i++ )
{
b++;
}
|
;_b$
= -4
;_i$ = -8
mov DWORD PTR _b$[ebp], 0
; b=0
; Loop Initilisation
mov DWORD PTR _i$[ebp], 0
jmp SHORT $L269
; Perform some function, each
time we loop
$L270:
mov eax, DWORD PTR _i$[ebp]
add eax, 1
mov DWORD PTR _i$[ebp], eax
; Check the i<10, if its false,
then we exit the loop
$L269:
cmp DWORD PTR _i$[ebp], 10
jge SHORT $L271
mov ecx, DWORD PTR _b$[ebp]
; b++ /|\
add ecx, 1
; b++ body
mov DWORD PTR _b$[ebp], ecx
; b++ \|/
jmp SHORT $L270
$L271: |
Another example C that is worth taking a look at, is if's ....e.g. if(true)
then do this.... now this should be nice and simple, well I hope it is...
| Comparison: If |
|
int b=0;
if( b==0 )
{
b++;
}
|
;_b$ = -4
mov DWORD PTR _b$[ebp], 0
; b=0
; Check if b is zero, and set any
flags, in the flags registers
cmp DWORD PTR _b$[ebp], 0
jne SHORT $L268
; Well if where here, then it was
true
mov eax, DWORD PTR _b$[ebp]
; b++ /|\
add eax, 1
; b++ body
mov DWORD PTR _b$[ebp], eax
; b++ \|/
; If failed so it jumps straight
here
$L268: |
|
