# 10.2. Customizing wrapper compiler behavior

The PMIx wrapper compiler is driven by text files that contain, among other things, the flags that are passed to the underlying compiler. The text file is generated automatically for PMIx and is customized for the compiler set that was selected when PMIx was configured; it is not recommended that users edit this file.

However, there are cases where it may be necessary or desirable to edit the file and add to or subtract from the flags that PMIx selected. The file is installed in `$pkgdatadir`, which defaults to `$prefix/share/pmix/pmixcc-wrapper-data.txt`. Several environment variables are also available for run-time replacement of the wrapper’s default values (from the text file):

Note

You may need to scroll right in the following table.

Wrapper compiler | Compiler | Preprocessor flags | Compiler flags | Linker flags | Linker library flags | Data file
--- | --- | --- | --- | --- | --- | ---
`mpmixcc` | `PMIX_CC` | `PMIX_CPPFLAGS` | `PMIX_CFLAGS` | `PMIX_LDFLAGS` | `PMIX_LIBS` | `pmixcc-wrapper-data.txt`

Caution

Note that changing the underlying compiler may not work at all.

The traditional method of using multiple different compilers with PMIx is to install PMIx multiple times; each installation should be built/installed with a different compiler. This is annoying, but it is beyond the scope of PMIx to be able to fix.

Note that the values of these fields can be directly influenced by passing flags to PMIx’s `configure` script. See this section in the Installation guide for more details.

The files cited in the above table use fairly simplistic “key=value” data formats. The following are several fields that are likely to be of interest to end-users:

- `project_short`: Prefix for all environment variables. See below.

- `compiler_env`: Specifies the base name of the environment variable that can be used to override the wrapper’s underlying compiler at run-time. The full name of the environment variable is of the form `<project_short>_<compiler_env>`; see table above.

- `compiler_flags_env`: Specifies the base name of the environment variable that can be used to override the wrapper’s compiler flags at run-time. The full name of the environment variable is of the form `<project_short>_<compiler_flags_env>`; see table above.

- `compiler`: The executable name of the underlying compiler.

- `extra_includes`: Relative to `$installdir`, a list of directories to also list in the preprocessor flags to find header files.

- `preprocessor_flags`: A list of flags passed to the preprocessor.

- `compiler_flags`: A list of flags passed to the compiler.

- `linker_flags`: A list of flags passed to the linker.

- `libs`: A list of libraries passed to the linker.

- `required_file`: If non-empty, check for the presence of this file before continuing. If the file is not there, the wrapper will abort saying that the language is not supported.

- `includedir`: Directory containing PMIx’s header files. The proper compiler “include” flag is prepended to this directory and added into the preprocessor flags.

- `libdir`: Directory containing PMIx’s library files. The proper compiler “include” flag is prepended to this directory and added into the linker flags.