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### 23.5 Source Files Containing Type Information

Whenever you add `GTY` markers to a source file that previously had none, or create a new source file containing `GTY` markers, there are three things you need to do:

1. You need to add the file to the list of source files the type machinery scans. There are four cases:
   1. For a back-end file, this is usually done automatically; if not, you should add it to `target_gtfiles` in the appropriate port’s entries in `config.gcc`.
   2. For files shared by all front ends, add the filename to the `GTFILES` variable in `Makefile.in`.
   3. For files that are part of one front end, add the filename to the `gtfiles` variable defined in the appropriate `config-lang.in`. Headers should appear before non-headers in this list.
   4. For files that are part of some but not all front ends, add the filename to the `gtfiles` variable of all the front ends that use it.
2. If the file was a header file, you’ll need to check that it’s included in the right place to be visible to the generated files. For a back-end header file, this should be done automatically. For a front-end header file, it needs to be included by the same file that includes `gtype-lang.h`. For other header files, it needs to be included in `gtype-desc.cc`, which is a generated file, so add it to `ifiles` in `open_base_file` in `gengtype.cc`.

   For source files that aren’t header files, the machinery will generate a header file that should be included in the source file you just changed. The file will be called `gt-path.h` where path is the pathname relative to the `gcc` directory with slashes replaced by `-`, so for example the header file to be included in `cp/parser.cc` is called `gt-cp-parser.h`. The generated header file should be included after everything else in the source file.

For language frontends, there is another file that needs to be included somewhere. It will be called `gtype-lang.h`, where lang is the name of the subdirectory the language is contained in.

Plugins can add additional root tables. Run the `gengtype` utility in plugin mode as `gengtype -P pluginout.h source-dir file-list plugin*.c` with your plugin files plugin*.c using `GTY` to generate the pluginout.h file. The GCC build tree is needed to be present in that mode.

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