notes

早期freebsd实现

gdb debugging of assembly sources:
	write a function linestab() that generates a .stabd symbol
		independently of the input
	write a function filestab() to generate a .stabs symbol
	we need to take especial care with #line directives
		since we want to handle locore, and locore is passed thru cpp
		this could be tough
	outline of a solution:
		cpp sends us lines of the form
			# logical-line "logical-file" trash
		these lines are interpreted ahead of the gas preprocess pass
		in the starting state, the logical filename is the same
			as the real filename (in case there're no #lines)
		the initial logical line number is 1
		every time we're ready to process a new instruction line,
			if the source file has changed,
				emit a .stabs for the logical file
			emit a .stabd for the logical line
			bump the logical line number
				can gas eat multiple actual lines in one insn?

i386 nits:
	jmp *$foo produces a short relative branch
	string quotes in comments
		Bill says gas eats text across newlines to find matches
		works fine for me
		I think it's most likely due to cpp
	make / no longer be a comment char
		it's now like the VAX: # is the only comment char
	incorrectly assembles lcall, int3, into, bsr/f instructions
	constant expressions fail if more than a few terms
		gives (low+2)*3+4*5 as an example
		works fine for me
	cpp seems to think $ is a valid literal
		use -$ in /usr/bin/cpp