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18. Miscellaneous Rules

There are a few rules and variables that didn't fit anywhere else.

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18.1 Interfacing to etags

Automake will generate rules to generate `TAGS' files for use with GNU Emacs under some circumstances.

If any C, C++ or Fortran 77 source code or headers are present, then tags and TAGS rules will be generated for the directory. All files listed using the _SOURCES, _HEADERS, and _LISP primaries will be used to generate tags. Note that generated source files that are not distributed must be declared in variables like nodist_noinst_HEADERS or nodist_prog_SOURCES or they will be ignored.

A tags rule will be output at the topmost directory of a multi-directory package. When run from this topmost directory, `make tags' will generate a `TAGS' file that includes by reference all `TAGS' files from subdirectories.

The tags rule will also be generated if the variable ETAGS_ARGS is defined. This variable is intended for use in directories that contain taggable source that etags does not understand. The user can use the ETAGSFLAGS to pass additional flags to etags; AM_ETAGSFLAGS is also available for use in `Makefile.am'.

Here is how Automake generates tags for its source, and for nodes in its Texinfo file:

ETAGS_ARGS = automake.in --lang=none \
 --regex='/^@node[ \t]+\([^,]+\)/\1/' automake.texi

If you add file names to ETAGS_ARGS, you will probably also want to define TAGS_DEPENDENCIES. The contents of this variable are added directly to the dependencies for the tags rule.

Automake also generates a ctags rule that can be used to build vi-style `tags' files. The variable CTAGS is the name of the program to invoke (by default ctags); CTAGSFLAGS can be used by the user to pass additional flags, and AM_CTAGSFLAGS can be used by the `Makefile.am'.

Automake will also generate an ID rule that will run mkid on the source. This is only supported on a directory-by-directory basis.

Finally, Automake also emits rules to support the GNU Global Tags program. The GTAGS rule runs Global Tags and puts the result in the top build directory. The variable GTAGS_ARGS holds arguments that are passed to gtags.

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18.2 Handling new file extensions

It is sometimes useful to introduce a new implicit rule to handle a file type that Automake does not know about.

For instance, suppose you had a compiler that could compile `.foo' files to `.o' files. You would simply define a suffix rule for your language:

        foocc -c -o $@ $<

Then you could directly use a `.foo' file in a _SOURCES variable and expect the correct results:

bin_PROGRAMS = doit
doit_SOURCES = doit.foo

This was the simpler and more common case. In other cases, you will have to help Automake to figure out which extensions you are defining your suffix rule for. This usually happens when your extension does not start with a dot. Then, all you have to do is to put a list of new suffixes in the SUFFIXES variable before you define your implicit rule.

For instance, the following definition prevents Automake from misinterpreting the `.idlC.cpp:' rule as an attempt to transform `.idlC' files into `.cpp' files.

SUFFIXES = .idl C.cpp
        # whatever

As you may have noted, the SUFFIXES variable behaves like the .SUFFIXES special target of make. You should not touch .SUFFIXES yourself, but use SUFFIXES instead and let Automake generate the suffix list for .SUFFIXES. Any given SUFFIXES go at the start of the generated suffixes list, followed by Automake generated suffixes not already in the list.

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18.3 Support for Multilibs

Automake has support for an obscure feature called multilibs. A multilib is a library that is built for multiple different ABIs at a single time; each time the library is built with a different target flag combination. This is only useful when the library is intended to be cross-compiled, and it is almost exclusively used for compiler support libraries.

The multilib support is still experimental. Only use it if you are familiar with multilibs and can debug problems you might encounter.

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