The modern way… using optimising C cross-compiler on Linux.

This is easier than expected, just install CC65. On any modern Linux, this is as easy as:

$ apt-get install cc65

You then get cc65 (the C compiler), ca65 (the assembler) and ld65 (the linker). They work pretty much the same as any modern toolset:

• Compile your .C source code using cc65, which will emit a .S assembly file
• Assemble your .S assembly listing using ca65, which will emit a .o binary object file
• Link your .o object files using ld65, possibly including the cc65 standard library, which will emit a .prg executable