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96
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1 An object file consists of a series of sections each of which contains a
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2 list of exported symbols, a list of incomplete references, and a list of
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3 "local" symbols which may be used in calculating incomplete references. Each
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4 section will obviously also contain the object code.
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5
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6 Exported symbols must be completely resolved to an address within the
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7 section it is exported from.
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8
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9 Each object file starts with a magic number and version number. The magic
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10 number is the string "LWOBJ16" for this 16 bit object file format. The only
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11 defined version number is currently 0. Thus, the first 8 bytes of the object
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12 file are:
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13
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14 4C574F424A313600
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15
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16 Each section has the following items in order:
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17
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18 * section name
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19 * flags
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20 * list of local symbols (and addresses within the section)
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21 * list of exported symbols (and addresses within the section)
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22 * list of incomplete references along with the expressions to calculate them
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23 * the actual object code
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24
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25 The section starts with the name of the section with a NUL termination
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26 followed by a series of flag bytes terminated by NUL. The following flag
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27 bytes are defined:
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28
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29 Byte Meaning
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30 00 no more flags
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31 01 section is BSS - no actual code is present
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32
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33 Either a NULL section name or end of file indicate the presence of no more
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34 sections.
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35
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36 Each entry in the exported and local symbols table consists of the symbol
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37 (NUL terminated) followed by two bytes which contain the value in big endian
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38 order. The end of a symbol table is indicated by a NULL symbol name.
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39
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40 Each entry in the incomplete references table consists of an expression
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41 followed by a 16 bit offset where the reference goes. Expressions are
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42 defined as a series of terms up to an "end of expression" term. Each term
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43 consists of a single byte which identifies the type of term (see below)
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44 followed by any data required by the term. Then end of the list is flagged
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45 by a NULL expression (only an end of expression term).
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46
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47 TERMTYPE Meaning
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48 00 end of expression
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49 01 integer (16 bit in big endian order follows)
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50 02 external symbol reference (NUL term symbol)
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51 03 local symbol reference (NUL term symbol)
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52 04 operator (1 byte operator number - see below)
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53 05 section base address reference
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54
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55 External references are resolved using other object files while local
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56 references are resolved using the local symbol table(s) from this file. This
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57 allows local symbols that are not exported to have the same names as
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58 exported symbols or external references.
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59
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60 The operator numbers are:
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61
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62 NUM OP
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63 01 + (plus)
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64 02 - (minus)
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65 03 * (times)
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66 04 / (divide)
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67 05 % (modulus)
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68 06 \ (integer division)
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69 07 bitwise and
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70 08 bitwise or
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71 09 bitwise xor
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72 0A boolean and
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73 0B boolean or
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74 0C - (unary negation, 2's complement)
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75 0D ^ (unary 1's complement)
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76
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77 An expression is represented in a postfix manner with both operands for
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78 binary operators preceding the operator and the single operand for unary
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79 operators preceding the operator.
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