Some notes on x86-64 assembler

x86-64 assembler is AMD's extension of the classic IA32 into 64 bits. It's expanded register set and associated calling sequence improvements make it a good deal easier to code.

A x86-64 assembler kernel should contain the following CPP lines at the beginning of the file:

#ifndef ATL_GAS_x8664
   #error "This kernel requires gas x86-64 assembler!"
#endif

This quick error exit keeps a non-x86-64 assembler from generating hundreds or thousands of spurious error messages during install.