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This option is used to automate dependency tracking.
This is the “emit make dependency file” option. This option takes an optional string argument ‘type’.
This option has some usage constraints. It:
This option behaves fairly closely to the way the -M series of
options work with the gcc compiler, except that instead of just
emitting the predecessor dependencies, this also emits the successor
dependencies (output target files). By default, the output dependency
information will be placed in <base-name>.d, but may also be
specified with -MF<file>. The time stamp on this file will be
manipulated so that it will be one second older than the oldest
primary output file.
The target in this dependency file will normally be the dependency
file name, but may also be overridden with -MT<targ-name>.
AutoGen will not alter the contents of that file, but it may create
it and it will adjust the modification time to match the start time.
NB: these second letters are part of the option argument, so
-MF <file> must have the space character quoted or omitted, and
-M "F <file>" is acceptable because the F is part of the
option argument.
-M may be followed by any of the letters M, F, P, T, Q, D, or G.
However, only F, Q, T and P are meaningful. All but F have somewhat
different meanings. -MT<name> is interpreted as meaning
<name> is a sentinel file that will depend on all inputs
(templates and definition files) and all the output files will depend
on this sentinel file. It is suitable for use as a real make target.
Q is treated identically to T, except dollar characters (’$’) are
doubled. P causes a special clean (clobber) phoney rule to be inserted
into the make file fragment. An empty rule is always created for
building the list of targets.
This is the recommended usage:
-MFwhatever-you-like.dep -MTyour-sentinel-file -MP |
and then in your Makefile, make the ‘autogen’ rule:
-include whatever-you-like.dep
clean_targets += clean-your-sentinel-file
your-sentinel-file:
autogen -MT$@ -MF$*.d .....
local-clean :
rm -f $(clean_targets)
|
The modification time on the dependency file is adjusted to be one
second before the earliest time stamp of any other output file.
Consequently, it is suitable for use as the sentinel file testifying
to the fact the program was successfully run. (-include is
the GNU make way of specifying "include it if it exists". Your make
must support that feature or your bootstrap process must create the
file.)
All of this may also be specified using the DEPENDENCIES_OUTPUT
or AUTOGEN_MAKE_DEP environment variables. If defined,
dependency information will be output. If defined with white space
free text that is something other than true, false,
yes, no, 0 or 1, then the string is taken
to be an output file name. If it contains a string of white space
characters, the first token is as above and the second token is taken
to be the target (sentinel) file as -MT in the paragraphs
above. DEPENDENCIES_OUTPUT will be ignored if there are
multiple sequences of white space characters or if its contents are,
specifically, false, no or 0.
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