# Deprecated Features

Capstone needs to support features which were removed by LLVM in the past.
Here we explain how to reintroduce them.

## Reintroduction

To get the old features back we copy them from the old `.td` files and include them in the new ones.

To include removed features from previous LLVM versions do the following:

1. Checkout the last LLVM version the feature was present.
2. Copy all feature related definitions into a `<ARCH>Deprecated.td` file.
3. Checkout the newest LLVM version again.
4. Wrap the different definition types in include guards. For example the `InstrInfo` definitions could be included in:

    ```
    #ifndef INCLUDED_CAPSTONE_DEPR_INSTR
    #ifdef CAPSTONE_DEPR_INSTR
    #define INCLUDED_CAPSTONE_DEPR_INSTR // Ensures it is only included once
    
    [Instruction definitions of removed feature]
    
    #endif // INCLUDED_CAPSTONE_DEPR_INSTR
    #endif // CAPSTONE_DEPR_INSTR
    ```

    _Note that the order of `#ifndef` and `#ifdef` matters (otherwise you'll get an error from `tblgen`)._

5. Include the definitions in the current definition files with:

    ```
    #define CAPSTONE_DEPR_INSTR
    include "<ARCH>Deprecated.md"
    ```

## Notes
- It is possible that you have to change some definitions slightly.
Because certain classes no longer exist or were replaced (e.g.: `GCCBuiltin` -> `ClangBuiltin`).
- Some new processors might need to have the feature flag (`Has<DeprecatedFeature>`) added
to their `UnsupportedFeatures` list.