I have been using SciTE as my main programming text editor and more recently to code in assembly but unfortunately it does not seem to have support for AT&T style syntax and GAS (GNU Assembler) directives only Intel. So I have modified the asm.properties file and updated it to include the following:

• All GAS directives e.g. .long .ascii
• 32bit and 64bit registers for AT&T syntax e.g. %rax %ecx
• GAS Instructions e.g. movl, pushl
• Opens .s file extensions when filtering by assembly

Most likely I am missing a few things so let me know! You can download the asm.properties file from here:

AT&T / GAS syntax highlighting for SciTE