|
295
|
1 This is the companion linker to LWASM. It reads object files generated by
|
|
|
2 LWASM and combines them into an actual binary.
|
|
|
3
|
|
|
4 During linking, each file is read into memory. A list of externally
|
|
|
5 referenced symbols is made along with where these symbols are referenced.
|
|
|
6 Each external reference is checked against all previously loaded files (in
|
|
|
7 order of loading) and if a match is found, a note of that fact is made and a
|
|
|
8 link between the previously loaded file and the current reference.
|
|
|
9
|
|
|
10 Once all files are loaded, the symbol table is checked for any symbols which
|
|
|
11 are still unresolved. If any are found, the linking process complains and
|
|
|
12 bails out.
|
|
|
13
|
|
|
14 Once all the object files have been read, the linker follows a
|
|
|
15 pre-determined script for the specified target or a script supplied by the
|
|
|
16 user to lay out the binary. The instructions from the script are followed
|
|
|
17 blindly as it is assumed the user knows what he is doing.
|
|
|
18
|
|
|
19 For each defined section, the linker begins constructing the section data by
|
|
|
20 resolving each instance of that section in the order it was encountered. All
|
|
|
21 symbols defined by that section (local or exported) are assigned addresses.
|
|
|
22 The exact offset into the final section data is recorded for any incomplete
|
|
|
23 references in that section. All section base address references are resolved
|
|
|
24 to actual addresses at this stage.
|
|
|
25
|
|
|
26 Once all sections have been laid out and addresses assigned to all symbols,
|
|
|
27 all incomplete references are resolved and the resulting value placed into
|
|
|
28 the appropriate data stream. If any references cannot be resolved at this
|
|
|
29 stage, the linker will complain and bail out.
|
|
|
30
|
|
|
31 Once all sections, symbols, and incomplete references have been resolved,
|
|
|
32 the binary will output as appropriate for the specified target.
|
|
|
33
|
|
|
34 See the file "scripts.txt" for information about linker scripts and the
|
|
|
35 restrictions based on the output target.
|
|
|
36
|
|
|
37 The following output targets are supported:
|
|
|
38
|
|
|
39 Raw: this is a raw binary with no header information, etc. Suitable for ROM
|
|
|
40 images, etc. By default, the raw target starts the binary at address 0, puts
|
|
|
41 any section named "init" first, then "code" and/or "text", then all other
|
|
|
42 non-bss sections, then all bss sections. Note that any "bss" type section
|
|
|
43 that exists anywhere but at the end of the binary (i.e. is between or before
|
|
|
44 one or more non-bss sections) will be included as a series of NUL bytes.
|
|
|
45
|
|
|
46 DECB: this creates a LOADM style binary according to the linker script. By
|
|
|
47 default, this target places the sections in the same order as the raw target
|
|
|
48 but implements a load address of $2000. bss sections will not be included in
|
|
|
49 the actual output. If a bss section appears between two non-bss sections, a
|
|
|
50 new output block will be created in the output file.
|
|
|
51
|
