Let me ask the question more specifically, with an example of
assembly version.
Consider the function below.
void Test()
{
int x, y, z;
x = 1;
if(x==1)
y=2;
else
y=3;
OtherStuff:
z = 4;
}
---------------
x = 1;
012313BE mov dword ptr [x],1
if(x==1)
012313C5 cmp dword ptr [x],1
012313C9 jne Test+34h (12313D4h)
y=2;
012313CB mov dword ptr [y],2
else
012313D2 jmp OtherStuff (12313DBh)
y=3;
012313D4 mov dword ptr [y],3
OtherStuff:
z = 4;
012313DB mov dword ptr [z],4
The assembly instruction corresponding to 'if(x==1)' is
012313C5 cmp dword ptr [x],1
So, if I am able to change the instruction at this address during
run-time to
012313C5 jmp OtherStuff (12313DBh)
Then, I will be able to permanently skip the condition checking.
Right?
Why is this not possible?
All the languages I have heard about allow the programmer to
change only the data in memory; not the instructions. The
programmer's thought process is controlled by this idea,
subconsciously.
Why can't we change the instructions at runtime? Is there any
fundamental issue with that?
Is it possible to do it through direct assembly coding?
Thanks,
Gopan
