# Extension Scripts - SourceGen Tutorial

6502bench

- Introduction
- About Disassembly
- Using SourceGen
  - Moving Around
  - Simple Edits
  - Labels & Symbols
  - Editing Data Operands
  - Generating Code
- Digging Deeper
  - String Formatting
  - Local Variables
  - Inline Data
  - Odds & Ends
- Advanced Topics
  - Address Tables
  - Extension Scripts
  - Visualizations
- Suggestions

## Extension Scripts

Some repetitive formatting tasks can be handled with automatic scripts. This is especially useful for inline data, which can confuse the code analyzer.

An earlier tutorial demonstrated how to manually mark bytes as inline data. We're going to do it a faster way. For this tutorial, start a new project with the `Generic 6502` profile, and in the SourceGen Examples/Tutorial directory select "Tutorial4".

We'll need to load scripts from the project directory, so we have to save the project. `File > Save`, use the default name ("Tutorial4.dis65").

Take a look at the disassembly listing. The file starts with a `JSR` followed by a string that begins with a small number. This appears to be a string with a leading length byte. We want to load a script that can handle that, so use `Edit > Project Properties`, select the `Extension Scripts` tab, and click `Add Scripts from Project`. The file browser opens in the project directory. Select the file "InlineL1String.cs", click `Open`, then `OK`.

Nothing happened. If you look at the script with an editor (and you know some C#), you'll see that it's looking for a `JSR` to a function called `PrintInlineL1String`. So let's give it one.

Double-click the `JSR` opcode on line $1000 to jump to address $1036. The only thing there is an `RTS`. It's supposed to be a routine that prints a string with a leading length byte, but for the sake of keeping the example code short it's just a place-holder. Use the curly toolbar arrow (or `Alt+LeftArrow`) to jump back to $1000.

This time, double-click the `JSR` operand ("`L1036`") to edit the operand. Click `Create Label`, and enter `PrintInlineL1String`. Remember that labels are case-sensitive; you must enter it exactly as shown. Hit `OK` to accept the label, and `OK` to close the operand editor.

If all went well, address $1003 should now be an L1 string "`How long?`", and address $100D should be another `JSR`.

The next `JSR` appears to be followed by a null-terminated string, so we'll need something that handles that.

Go back into Project Properties and add the script called "InlineNullTermString.cs" from the project directory. This script is slightly different, in that it handles any `JSR` to a label that starts with `PrintInlineNullString`. So let's give it a couple of those.

Double-click the operand on line $100D ("`L1037`"), click `Create Label`, and set the label to "`PrintInlineNullStringOne`". Hit `OK` twice. That formatted the first one and got us to the next `JSR`. Repeat the process on line $1019 ("`L1038`"), setting the label to "`PrintInlineNullStringTwo`".

Things are looking good, but we've got one left, and it's got a twist. Instead of a string, the `JSR` at $1025 is followed by a pointer to a string. We'd like to format the pointer as an address, and then format the string it points to.

We're going to add a third extension script. Sometimes it's convenient to collect all inline data handlers for a project into a single script, so we'll demonstrate that here. The new script handles the previous two cases as well as this new case. Go into Project Properties, click the Extension Scripts tab, select the two scripts you added earlier, and click Remove. Then add the script "InlineMulti.cs" from the project directory. Click `OK` twice. Note that the strings formatted earlier remain formatted.

Double-click the operand on line $1025 ("`L1039`"), click `Create Label`, and set the label to "`PrintInlineAddrString`". Hit `OK` twice. This formatted the address at $1028, and also formatted the string at $102b as a null-terminated string. Because the bytes were formatted as an address and not a just a 16-bit value, a label was generated automatically.

The entire project is now nicely formatted. In a real project the "Print Inline" locations would be actual print functions, not just `RTS` instructions. There would likely be multiple `JSR`s to the print function, so labeling a single function entry point could format dozens of inline strings and clean up the disassembly automatically. The reason for allowing wildcard names is that some functions may have multiple entry points or chain through different locations.

Extension scripts can make your life much easier, but they do require some programming experience. See the SourceGen manual for more details.

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