@TomF So what I am looking for is neither nasm nor masm, but rather "Intel syntax". Clang and GCC both have modes in which they purport to follow "Intel syntax". To me, this is like Clang and GCC promising that an "Intel syntax" exists. From my research, unless there's a BNF I haven't found hiding in this 5000 page Intel x86_64 manual ( https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html ) , Intel has never defined such a thing. It was apparently only *implied* by examples in 8086 datasheets. (1/2)