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Added tag lwtools-4.4 for changeset 74b4e9f23c62
author lost@l-w.ca
date Wed, 10 Aug 2011 19:16:23 -0600
parents 2c24602be78f
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1 LWASM Internals
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2 ===============
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3
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4 LWASM is a table-driven assembler that notionally uses two passes. However,
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5 it implements its assembly in several passes as follows.
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7 Pass 1
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8 ------
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10 This pass reads the entire source code and parses each line into an internal
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11 representation. Macros, file inclusions, and conditional assembly
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12 instructions are resolved at this point as well. Instructions with known
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13 sizes will have their sizes resolved at this point.
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15 Pass 2
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16 ------
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18 Check all exported symbols for validity and set them as imports if the
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19 assembler state says so. Also resolve all symbol references in all
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20 expressions to be direct references either to the symbol table or
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21 to the import list.
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23 Pass 3
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24 ------
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26 This pass resolves all instruction sizes that can be resolved without
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27 forcing any instruction sizes. This pass will run repeatedly until no
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28 no new resolution occurs.
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30 Pass 4
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31 ------
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33 Work through all un-resolved instructions and force sizes. After each size
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34 is forced, try re-resolving all other instructions. This is done starting
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35 at the beginning of the source and working forward. If any instruction does
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36 not resolve when forced, an error will be thrown.
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38 Pass 5
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39 ------
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41 Constantize all line addresses and throw errors if any cannot be. This
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42 pass will repeat until no further lines addresses are reduced to constants
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43 at which time all lines will be checked for constant-ness.
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45 Pass 6
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46 ------
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48 Finalize all expressions related to instructions. Carp about any that
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49 cannot be reduced to a usable form. That means, for the non-object target
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50 all expressions must resolve to a constant. For the object form, all
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51 expressions must resolve to symbol references and constants. Those symbol
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52 references may be internal or external.
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54 Pass 7
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55 ------
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57 Emit object code for each line for later output.