os_query_stackBottom() how does it work?

[Chad J]

I've run into this while trying to port GPhobos to the arm-wince 
(PocketPC) platform.  Never mind that it's GPhobos though, it's the same 
function in dmd Phobos, Ares too.

It looks like this:

/**********************************************
  * Determine "bottom" of stack (actually the top on Win32 systems).
  */

void *os_query_stackBottom()
{
     asm
     {
	naked			;
	mov	EAX,FS:4	;
	ret			;
     }
}

I hit it while compiling std/thread.d, but I've also found it in 
internal/gc/win32.d.

I'm wondering how to do this without using assembly, or if assembly is 
necessary then how I might do it in ARM assembly.  I'd probably be on my 
way just to have some background knowledge about this though.  Knowledge 
like, what exactly is the stack bottom?  Is it the place you reach when 
you run out of stack memory or when you first start using the stack? 
Something else?  At least a link to some info would help.

It would be better though if someone knew how to do this using 
Win32/WinCE programming, and could show me that.

Google hasn't helped me much in determining how that code works, but it 
did yield some possibly useful information about WinCE memory architecture:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wcemain4/html/_wcesdk_Windows_CE_Memory_Architecture.asp
clicking "stack" at the bottom of that page leads to:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wcemain4/html/_wcesdk_the_stack.asp
This might also help:
http://blogs.msdn.com/kitlfirst/
searching WinCE API for "CreateThread" found in above article yields:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wcesdkr/html/wce30oriWindowsCE30APIReference.asp

Anyhow I might be able to improvise something using info from those 
links, but I am not sure what's happening on the Phobos side of things. 
  Please help.