12. Linking

After you have produced one or more object files and perhaps some library files, you might want to link them together to produce a ROM image / program file. WLALINK is the program you use for that. Here’s how you use it:

wlalink [OPTIONS] <LINK FILE> <OUTPUT FILE>

Choose the option -b [OUT] for program file or -r [OUT] for ROM image linking. ROM image is all the data in the ROM banks. Program file is the data between the first used byte and the last used byte. You can also use -bS [START ADDRESS] and -bE [END ADDRESS] to specify the start and the end addresses of the program. Both are optional.

Link file is a text file that contains information about the files you want to link together. Here’s the format:

1. You must define the group for the files. Put the name of the group inside brackets. Valid group definitions are

   [objects]
   [libraries]
   [header]
   [footer]
   [definitions]
   [ramsections]
   [sections]
   [sectionwriteorder]
   [ramsectionwriteorder]
   

2. Start to list the file names.

   [objects]
   main.o
   vbi.o
   level_01.o
   ...
   

3. Give parameters to the library files:

   [libraries]
   bank 0 slot 1 speed.lib
   bank 4 slot 2 map_data.lib
   ...
   

   Here you can also use base to define the 65816 CPU bank number (like .BASE works in WLA):

   [libraries]
   bank 0 slot 1 base $80 speed.lib
   bank 4 slot 2 base $80 map_data.lib
   ...
   

   You must tell WLALINK the bank and the slot for the library files.

4. If you want to use header and/or footer in your project, you can type the following:

   [header]
   header.dat
   [footer]
   footer.dat
   

5. If you have RAMSECTIONs inside the libraries, you must place the sections inside BANKs and SLOTs (ORG and ORGA are optional). Note that you can also change the type and priority of the section, and can use appendto:

   [ramsections]
   bank 0 slot 3 org $0 "library 1 vars 1"
   bank 0 slot 3 orga $6100 priority 100 force "library 1 vars 2"
   bank 0 slot 3 appendto "library 1 vars 2" "library 1 vars 3"
   

6. If you want to relocate normal sections, do as follows (ORG, ORGA, KEEP, AFTER, OFFSET, PRIORITY, WINDOW, BITWINDOW and APPENDTO are optional, but useful):

   [sections]
   bank 0 slot 1 org $100 appendto "MusicPlayers" "MusicPlayer1"
   bank 0 slot 1 orga $2200 semisubfree priority 100 keep bitwindow 8 "EnemyAI"
   bank 0 slot 2 after "Enemies" offset 256 "Dragon"
   

7. If you want to make value definitions, here’s your chance:

   [definitions]
   debug 1
   max_str_len 128
   start $150
   ...
   

8. If you want to change the order in which the linker writes the sections to output:

   [sectionwriteorder]
   OVERWRITE
   FORCE
   FREE
   SEMISUPERFREE
   SEMISUBFREE
   SEMIFREE
   SUPERFREE
   

9. If you want to change the order in which the linker writes the RAM sections to output:

   [ramsectionwriteorder]
   FREE
   FORCE
   SEMISUBFREE
   SEMIFREE
   

Note that you have to specify all the section types here.

If flag v is used, WLALINK displays information about ROM file after a succesful linking.

If flag R is used the file paths inside the link file are relative to the directory where the link file is, not relative to current working directory.

If flag nS is used, WLALINK doesn’t sort the sections at all, so they are placed in the output in their order of appearance.

If flag s is used, WLALINK will produce a NO$GMB/NO$SNES symbol file. It’s useful when you work under MSDOS (NO$GMB is a very good Game Boy emulator for MSDOS/Windows) as it contains information about the labels in your project.

If flag S is used, WLALINK will create a WLA symbol file, that is much like NO$GMB symbol file, but shows also symbols, defines, and breakpoints, not just labels.

If flag d is used, WLALINK discards all unreferenced FREE, SEMIFREE, SEMISUBFREE, SUPERFREE and RAM sections. This way you can link big libraries to your project and WLALINK will choose only the used sections, so you won’t be linking any dead code/data.

If flag D is used, WLALINK doesn’t create any _sizeof_* labels. Note that to disable fully _sizeof_* label creation, you’ll also need to give WLA the s flag.

If flag pS is used then WLALINK doesn’t use section type in writing the .SECTION s, but instead uses just the PRIORITY (and size) when it writes the .SECTION s to output.

Flag pR works the same as pS but for .RAMSECTION s.

If flag t is used with c64PRG, WLALINK will add a two byte header to the program file (use with flag b). The header contains the load address for the PRG. Use the flag a to specify the load address. It can be a value or the name of a label.

If flag i is given, WLALINK will write list files. Note that you must compile the object and library files with -i flag as well. Otherwise WLALINK has no extra information it needs to build list files. Here is an example of a list file: Let’s assume you’ve compiled a source file called main.s using the i flag. After you’ve linked the result also with the i flag WLALINK has created a list file called main.lst. This file contains the source text and the result data the source compiled into. List files are good for debugging. NOTE: list file data can currently be generated only for code inside sections. .MACRO calls and .REPT s don’t produce list file data either.

If flag L is given after the above options, WLALINK will use the directory specified after the flag for including libraries. If WLALINK cannot find the library in the specified directory, it will then silently search the current working directory. This is useful when using WLA in an SDK environment where a global path is needed.

Make sure you don’t create duplicate labels in different places in the memory map as they break the linking loop. Duplicate labels are allowed when they overlap each other in the destination machine’s memory. Look at the following example:

...
.BANK 0
.ORG $150

    ...
    LD      A, 1
    CALL    LOAD_LEVEL
    ...

LOAD_LEVEL:
    LD      HL, $2000
    LD      (HL), A
    CALL    INIT_LEVEL
    RET

.BANK 1
.ORG 0

INIT_LEVEL:
    ...
    RET

.BANK 2
.ORG $0

INIT_LEVEL:
    ...
    RET
...

Here duplicate INIT_LEVEL labels are accepted as they both point to the same memory address (in the program’s point of view).

Note that when you use .RAMSECTIONs, WLALINK will generate labels RAM_USAGE_SLOT_[slot name/id]_BANK_[bank number]_START and RAM_USAGE_SLOT_[slot name/id]_BANK_[bank number]_END that contain the addresses of the first and last used byte in the RAM bank/slot. Note that this only uses .RAMSECTION information to calculate the addresses, not .ENUMs or anything else.

Examples:

[seravy@localhost tbp]# wlalink -r linkfile testa.sfc
[seravy@localhost tbp]# wlalink -d -i -b linkfile testb.sfc
[seravy@localhost tbp]# wlalink -v -S -L ../../lib linkfile testc.sfc
[seravy@localhost tbp]# wlalink -v -b -s -t c64PRG -a LOAD_ADDRESS linkfile linked.prg