MASM64 running 64bit Mode instead of 64bit compatibility mode

Question

ML64.exe seems to compile and run in 64bit compatibility mode instead of 64bit mode. I assume this because it seems virtualized in windows 8. Is there a way to force, or compile into, 64bit mode in windows 8?

Answer 1

ML64.exe can compile on a 32-bit Windows system, since it is a 32-bit program, and on a 64-bit Windows system, since all 64-bit Windows systems have the WoW64 subsystem that runs 32-bit programs in a 32-bit environment. Therefore, ML64.exe does not assemble in 64-bit mode. However, ML64.exe can assemble code for 64-bit mode. You can test this by using a 64-bit specific instruction, such as MOVSQ (Move qword from RSI to RDI).