10. 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.

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

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]
```
Start to list the file names.
```
[objects]
main.o
vbi.o
level_01.o
...
```
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.
If you want to use header and/or footer in your project, you can type the following:
```
[header]
header.dat
[footer]
footer.dat
```
If you want to make value definitions, here’s your chance:
```
[definitions]
debug 1
max_str_len 128
start $150
...
```

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

If flag s is used, WLALINK will produce a NO$GMB symbol file. It’s useful when you work under MSDOS (NO$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 and breakpoints, not just labels and definitions.

If flag d is used, WLALINK discards all unreferenced FREE and SEMIFREE 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 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.

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).

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