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1 This is the companion linker to LWASM. It reads object files generated by
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2 LWASM and combines them into an actual binary.
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3
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4 During linking, each file is read into memory. A list of externally
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5 referenced symbols is made along with where these symbols are referenced.
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6 Each external reference is checked against all previously loaded files (in
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7 order of loading) and if a match is found, a note of that fact is made and a
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8 link between the previously loaded file and the current reference.
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9
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10 Once all files are loaded, the symbol table is checked for any symbols which
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11 are still unresolved. If any are found, the linking process complains and
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12 bails out.
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13
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14 Once all the object files have been read, the linker follows a
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15 pre-determined script for the specified target or a script supplied by the
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16 user to lay out the binary. The instructions from the script are followed
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17 blindly as it is assumed the user knows what he is doing.
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18
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19 For each defined section, the linker begins constructing the section data by
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20 resolving each instance of that section in the order it was encountered. All
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21 symbols defined by that section (local or exported) are assigned addresses.
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22 The exact offset into the final section data is recorded for any incomplete
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23 references in that section. All section base address references are resolved
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24 to actual addresses at this stage.
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25
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26 Once all sections have been laid out and addresses assigned to all symbols,
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27 all incomplete references are resolved and the resulting value placed into
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28 the appropriate data stream. If any references cannot be resolved at this
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29 stage, the linker will complain and bail out.
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30
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31 Once all sections, symbols, and incomplete references have been resolved,
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32 the binary will output as appropriate for the specified target.
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33
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34 See the file "scripts.txt" for information about linker scripts and the
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35 restrictions based on the output target.
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36
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37 The following output targets are supported:
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38
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39 Raw: this is a raw binary with no header information, etc. Suitable for ROM
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40 images, etc. By default, the raw target starts the binary at address 0, puts
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122
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41 any section named "init" first, then "code", then all other non-bss
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42 sections, then all bss sections. Note that any "bss" type section that
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43 exists anywhere but at the end of the binary (i.e. is between or before one
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44 or more non-bss sections) will be included as a series of NUL bytes.
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113
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45
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46 DECB: this creates a LOADM style binary according to the linker script. By
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47 default, this target places the sections in the same order as the raw target
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48 but implements a load address of $2000. bss sections will not be included in
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49 the actual output. If a bss section appears between two non-bss sections, a
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50 new output block will be created in the output file.
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51
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