1. The input is a C-like preprocessed source, the output is a NASM-like strip.
	dg	-> define gadget, which must be slid by library slide
	du	-> define local, which must be slid by strip slide
	dd	-> define data (%define dd -> dq for 64bit)

2. we implement lazy assignment.  that is, an assignment is not guaranteed
    to generate code, it only guarantees that when first using the assigned
    variable, it will have the desired value.  however, since we do not have
    proper flow analysis, any assignment in a loop cannot be lazy. see 'const'

3. immediate expressions involving local pointers cannot be simplified, unless
    they can be reduced to: PTR + scalar.  that is because there is one single
    final addition applied by the assembler, after full evaluation.

4. strings are treated as implicit addresses.  therefore,
	b = "a" + 1
    really means:
	str = "a"
	b = &str + 1
    also, compound expressions are treated just like strings, with "long"
    values instead of characters

5. imports are implicit addresses.  to actually use external variables, do
	*optind = 0;
	a = *optind;

6. sometimes, it is better to use multiple assignments for the same value
	fd = fd2 = open(...);
	read(fd, ...);
	close(fd2);
    instead of
	fd = open(...);
	read(fd, ...);
	close(fd);

7. this contrived load/store architecture stems from the assumptions that
    some rop gadgets are hard -- or impossible -- to find.  for example,
    it is hard to load r1 without r0

8. jumping to labels in the past is tricky, because stack above us is
    destroyed by calls in-between.  for the same reason, parameters
    referencing things in the past are WRONG:
	label:
	x = 1;
	printf("x=%x\n", x);
	if (modify(&x)) goto label;
    stack above modify is destroyed, so jumping back to label is problematic.
    also, any use of *(&x) is probably doomed.  therefore, we need to reserve
    some stack space before any such calls. see '[[stack]]'

====

const:
    used for
	var = immediate
    to avoid generating
	*&var = immediate
    var is inlined and defined as immediate, when possible
    useful inside loops

volatile:
    used for
	x = var
    to force generating
	x = *&var
    var is never inlined
    needed when a variable is used before and after a function call

therefore
    "const volatile" is perfectly ok :)
    because the var will never be inlined, but will not generate code for assignment

====

extern function[[attr]];
a = function;
a();		will not respect import attributes
[[attr]]a();	will respect call attributes