Is it possible to use 64-bit instruction in a 32-bit application on intel/64-bit win7

Question

My environment is 64-bit win7, VC2010.

Of course, the intel inside is 64-bit CPU.

Can I use the 64-bit instruction/native machine word(64-bit) in a 32-bit ap

Answer 1

Actually, you kind of can. The mechanism used to switch from 32 to 64 bit mode (which clearly must exist on a 64 bit OS capable of running 32 bit code) is not in any way protected, and can be used from user code. On Windows it is called Heaven's Gate, and it's pretty simple: just a far call with a segment selector of 33h.

So, how to run 64bit code?

call 33h:your64bitcode
...
your64bitcode:
; do something
retf

There are, of course, some limitations to what you can do from 64bit code entered in that way, because you're not truly in a 64bit process.