Question

I have asm file that can be assembled for x64 and x86 using masm (ml.exe or ml64.exe). Is there some predefined macro in masm to detect that file is being assembled for x64? Right now i manually defined _WIN64 and then test for it, but there must be a better way to check that.

Answer 1

You can try testing if RAX is defined, as suggested in one of the answers to this similar question: Detecting architecture at compile time from MASM/MASM64

I use this trick to create a variable that will stop my x64 asm code from being assembled in x32 builds

IFDEF RAX
    END_IF_NOT_X64 equ <>
ELSE
    END_IF_NOT_X64 equ end  ; kill stop the assembler if we're not compiling for x64
ENDIF

END_IF_NOT_X64

; x64 code...