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Added pass2 and various supporting logic including symbol lookups
author lost@starbug
date Tue, 06 Apr 2010 21:03:19 -0600
parents e7885b3ee266
children 6a98cc90c14f
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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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14
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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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25
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26 This pass resolves all instruction sizes that can be resolved without
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27 setting addresses for instructions. This process is repeated until no
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28 further instructions sizes are resolved.
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30 Pass 4
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31 ------
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33 This pass assigns addresses to all symbols where values are known. It does
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34 the same for instructions. Then a repeat of similar algorithms as in the
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35 previous pass is used to resolve as many operands as possible.
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36
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37 This pass is repeated multiple times until no further instructions or
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38 symbols are resolved.
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40 Pass 5
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41 ------
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43 Finalization of all instruction sizes by forcing them to the maximum
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44 addressing mode. Then all remaining instruction addresses and symbol values
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45 are resolved.
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47 Pass 6
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48 ------
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49
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50 This pass does actual code generation. This is the notional second pass. All
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51 other passes are the notional first pass.
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54 Expression Evaluation
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55 =====================
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56
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57 Each expression carries a certainty flag. Any expression in which any term
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58 is flagged as uncertain is, itself, uncertain. There are a few specific
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59 cases where such uncertainty can cancel out. For instance, X-X where X is
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60 uncertain is guaranteed to be 0 and so there is no uncertainty.
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