MASM/NASM Differences

Question

What are the syntax differences between the NASM and MASM assemblers?

Solution

Section 2.2 of the NASM documentation is titled Quick Start for MASM Users which lists the important differences between NASM and MASM.

Comments

[Peter Cordes]

Related: How to know if an assembly code has particular syntax (emu8086, NASM, TASM, ...)? shows some syntax diff examples.

[Admin]

in that section is stated: "NASM Is Case-Sensitive" However, MASM also can be case-sensitive, simply use: option casemap :none

[Peter Cordes]

GAS / llvm-as in .intel_syntax noprefix mode use syntax that's pretty much MASM for instructions, but with directives that are specific to them.

[Peter Cordes]

nasm -felf64 foo.asm should work the same way no matter what host you're building on. If you have some asm files that assemble on Linux but not Windows, it's probably because of building with different bitness (e.g. nasm -fwin32 vs. nasm -felf64), or something about directives, or possibly the .asm uses %if conditional stuff an does something different on Windows.) Without an example of the instructions, it's not useful to say that NASM on windows errors. What, on every file in general? No, of course not.