Cheat Engine

[Slugsnack]

[atom0s]

Question for you Burningmace, is this topic created with the intent of actually learning or because you are doing a challenge on a site such as HackQuest and are looking for help with one of their challenges? I'm asking since this exact topic is one of their challenges, so looked familiar.

[Polynomial]

Slugsnack, actually it has been two teachers and multiple online learning references that have steered me away from recursion. I guess it's something that people avoid due to the somewhat difficult and troublesome nature of it. I know that Haskell uses it in a lot of situations, but I remember reading somewhere that the stack in Haskell is automatically expanded if it gets near the limit.

Wiccaan, it is just a learning topic. I've never heard of HackQuest, it looks interesting. I shall take a look when I have time.

[Flyte]

[Slugsnack]

[Polynomial]

Slugsnack - That may well have been where I read it. I've been rather tired recently (download festival, woooo!) so I forget things easily Does this stack probe mechanism hold for all languages? I remember back in the days of VB6 it was annoyingly easy to cause a stack overflow with recursive code - I forget the exact number of calls that killed it but it wasn't a lot, in the order of a few thousand I think. In fact, VB6 tutorials were where I got a lot of my "recursion is bad" lectures from.

Flyte - Useful and recursive in high level terms, but does it result in recursive or iterative code at assembly level? A friend asserted to me that languages with inherent "recursivity" are often compiled into an iterative form. He went on to state that some compilers even give each expression its own "virtual stack" which eliminates the problems of using the standard stack with call/ret. Regardless, this thread is a catalog of why recursion can be good. I'll regard it in higher terms in future.

[Slugsnack]

The stack being extended does not mean it can't overflow. Just means there is a large space that is reserved but it is only committed to a certain size which can then keep growing up to the reserved size.

[Polynomial]

From the way I read it (it may not have been your post) it suggested that the stack would expand as much as possible, to the limit of as much memory that can be allocated by a single process. Think of it as the Stack class in the .NET framework, where the whole stack is simply an object in virtual memory and not the traditional stack pointed to by the ESP register. Each entry added allocates more memory automatically.

[Slugsnack]

The stack must be all in contiguous memory and it can not simply be moved around to reallocate it like with realloc() or something because it would involve having to update ESP + ESP + PE headers, etc.

Each thread has a block of memory reserved for the stack. Only a proportion of that memory is committed and then the guard page will expand the committed memory. I believe the reason it's implemented like this is so you don't end up wasting tonnes of memory on unused stack memory.

[Polynomial]

I was talking more about a 'virtualised' system, where instructions would be translated into low level code but the higher level program stack kept in more managed conditions. I imagine this is how interpreted script languages such as PHP work.

For example, I could write code in C# that parsed a set of imitation low level instructions (including call/ret/push/pop equivilents) and modified the state of a large byte array (virtual memory) and a stack object (the virtual stack) as normal programs would do. This would create similar results to that of a native executable program (albeit with a significant performance hit) yet never directly access the real stack - the whole thing would remain managed. The managed stack in CIL is similar to this, where all CIL code is executed by the virtual machine.

But all of this is off topic. Challenges please!

[Deltron Z]

We've already solved your challanges.
I solved the first 3 in C/C++ and Flyte gave another solution in what seems like C#, is this J#? looks cool, I didn't even know they still use it...

[Slugsnack]

F#