EXTRN XYZ (XYZ is constant)

mov eax, XYZ => OK

But,

DW XYZ => error:invalid use of symbol

How can I do define-byte from external constants?

Both ELF anf COFF format don't have an 8-bit type of relocation, and as for the 16-bit one, it's only COFF that has the code reserved for such type, but it is said to be not supported anyway. For this reason fasm is able to generate only 32-bit and 64-bit relocations, thus if you define XYZ as external (and thus it needs relocation to be filled with right value), you can use it only with either DD or DQ - that's why you've got the above error.

Thanks a lot.

dd constant is OK!.

But, it seems inconvenient for some cases

like dw selector-constant.

Thanks anyway