How to get address of base stack pointer

The really right thing to do would be to rewrite whatever this function does so that it does not require access to the actual frame pointer. That is definitely bad behavior.

But, to do what you are looking for you should be able to do:

int CallStackSize() {
    __int64 Frame = 0; /* MUST be the very first thing in the function */
    PDWORD pFrame;

    Frame++; /* make sure that Frame doesn't get optimized out */

    pFrame = (PDWORD)(&Frame);
    /*... do stuff with pFrame here*/
}

The reason this works is that in C usually the first thing a function does is save off the location of the base pointer (ebp) before allocating local variables. By creating a local variable (Frame) and then getting the address of if, we're really getting the address of the start of this function's stack frame.

Note: Some optimizations could cause the "Frame" variable to be removed. Probably not, but be careful.

Second Note: Your original code and also this code manipulates the data pointed to by "pFrame" when "pFrame" itself is on the stack. It is possible to overwrite pFrame here by accident and then you would have a bad pointer, and could get some weird behavior. Be especially mindful of this when moving from x86 to x64, because pFrame is now 8 bytes instead of 4, so if your old "do stuff with pFrame" code was accounting for the size of Frame and pFrame before messing with memory, you'll need to account for the new, larger size.

There is no guarantee that RBP (the x64's equivalent of EBP) is actually a pointer to the current frame in the callstack. I guess Microsoft decided that despite several new general purpose registers, that they needed another one freed up, so RBP is only used as framepointer in functions that call alloca(), and in certain other cases. So even if inline assembly were supported, it would not be the way to go.

If you just want to backtrace, you need to use StackWalk64 in dbghelp.dll. It's in the dbghelp.dll that's shipped with XP, and pre-XP there was no 64-bit support, so you shouldn't need to ship the dll with your application.

For your 32-bit version, just use your current method. Your own methods will likely be smaller than the import library for dbghelp, much less the actual dll in memory, so it is a definite optimization (personal experience: I've implemented a Glibc-style backtrace and backtrace_symbols for x86 in less than one-tenth the size of the dbghelp import library).

Also, if you're using this for in-process debugging or post-release crash report generation, I would highly recommend just working with the CONTEXT structure supplied to the exception handler.

Maybe some day I'll decide to target the x64 seriously, and figure out a cheap way around using StackWalk64 that I can share, but since I'm still targeting x86 for all my projects I haven't bothered.

You can use the _AddressOfReturnAddress() intrinsic to determine a location in the current frame pointer, assuming it hasn't been completely optimized away. I'm assuming that the compiler will prevent that function from optimizing away the frame pointer if you explicitly refer to it. Or, if you only use a single thread, you can use the IMAGE_NT_HEADER.OptionalHeader.SizeOfStackReserve and IMAGE_NT_HEADER.OptionalHeader.SizeOfStackCommit to determine the main thread's stack size. See this for how to access the IMAGE_NT_HEADER for the current image.

I would also recommend against using IsBadWritePtr to determine the end of the stack. At the very least you will probably cause the stack to grow until you hit the reserve, as you'll trip a guard page. If you really want to find the current size of the stack, use VirtualQuery with the address you are checking.

And if the original use is to walk the stack, you can use StackWalk64 for that.

Microsoft provides a library (DbgHelp) which takes care of the stack walking, and you should use instead of relying on assembly tricks. For example, if the PDB files are present, it can walk optimized stack frames too (those that don't use EBP).

CodeProject has an article which explains how to use it:

http://www.codeproject.com/KB/threads/StackWalker.aspx