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The rules and dependency trees generated by automake
can get
rather complex, and leave the developer head-scratching when things
don’t work as expected. Besides the debug options provided by the
make
command (see Options Summary in The GNU Make
Manual), here’s a couple of further hints for debugging makefiles
generated by automake
effectively:
make V=1
to see the commands being executed.
make -n
can help show what would be done without actually doing
it. Note however, that this will still execute commands prefixed
with ‘+’, and, when using GNU make
, commands that contain
the strings ‘$(MAKE)’ or ‘${MAKE}’ (see Instead of
Execution in The GNU Make Manual).
Typically, this is helpful to show what recursive rules would do, but it
means that, in your own rules, you should not mix such recursion with
actions that change any files.7 Furthermore, note that GNU make
will update
prerequisites for the Makefile file itself even with -n
(see Remaking Makefiles in The GNU Make Manual).
make SHELL="/bin/bash -vx"
can help debug complex rules.
See The Make Macro SHELL in The Autoconf Manual, for some
portability quirks associated with this construct.
Automake’s ‘dist’ and ‘distcheck’ rules had a bug in this regard in that they created directories even with -n, but this has been fixed in Automake 1.11.