## 20 Makefile Fragments

When you configure GCC using the `configure` script, it will construct the file `Makefile` from the template file `Makefile.in`. When it does this, it can incorporate makefile fragments from the `config` directory. These are used to set Makefile parameters that are not amenable to being calculated by autoconf. The list of fragments to incorporate is set by `config.gcc` (and occasionally `config.build` and `config.host`); See System Config.

Fragments are named either `t-target` or `x-host`, depending on whether they are relevant to configuring GCC to produce code for a particular target, or to configuring GCC to run on a particular host. Here target and host are mnemonics which usually have some relationship to the canonical system name, but no formal connection.

If these files do not exist, it means nothing needs to be added for a given target or host. Most targets need a few `t-target` fragments, but needing `x-host` fragments is rare.