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Initial import from lwtools 3.0.1 version, with new hand built build system and file reorganization
author lost@l-w.ca
date Wed, 19 Jan 2011 22:27:17 -0700
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1 LWASM Internals
2 ===============
3
4 LWASM is a table-driven assembler that notionally uses two passes. However,
5 it implements its assembly in several passes as follows.
6
7 Pass 1
8 ------
9
10 This pass reads the entire source code and parses each line into an internal
11 representation. Macros, file inclusions, and conditional assembly
12 instructions are resolved at this point as well. Instructions with known
13 sizes will have their sizes resolved at this point.
14
15 Pass 2
16 ------
17
18 Check all exported symbols for validity and set them as imports if the
19 assembler state says so. Also resolve all symbol references in all
20 expressions to be direct references either to the symbol table or
21 to the import list.
22
23 Pass 3
24 ------
25
26 This pass resolves all instruction sizes that can be resolved without
27 forcing any instruction sizes. This pass will run repeatedly until no
28 no new resolution occurs.
29
30 Pass 4
31 ------
32
33 Work through all un-resolved instructions and force sizes. After each size
34 is forced, try re-resolving all other instructions. This is done starting
35 at the beginning of the source and working forward. If any instruction does
36 not resolve when forced, an error will be thrown.
37
38 Pass 5
39 ------
40
41 Constantize all line addresses and throw errors if any cannot be. This
42 pass will repeat until no further lines addresses are reduced to constants
43 at which time all lines will be checked for constant-ness.
44
45 Pass 6
46 ------
47
48 Finalize all expressions related to instructions. Carp about any that
49 cannot be reduced to a usable form. That means, for the non-object target
50 all expressions must resolve to a constant. For the object form, all
51 expressions must resolve to symbol references and constants. Those symbol
52 references may be internal or external.
53
54 Pass 7
55 ------
56
57 Emit object code for each line for later output.