Question

We have a long and complicated Makefile in our build system. Is there a good way to trace exactly which targets get executed for a given make invocation?

Answer 1

Use make -d or make --debug[=flags] options:

‘-d’

Print debugging information in addition to normal processing. The debugging information says which files are being considered for remaking, which file-times are being compared and with what results, which files actually need to be remade, which implicit rules are considered and which are applied—everything interesting about how make decides what to do. The -d option is equivalent to ‘--debug=a’ (see below).

‘--debug[=options]’

Print debugging information in addition to normal processing. Various levels and types of output can be chosen. With no arguments, print the “basic” level of debugging. Possible arguments are below; only the first character is considered, and values must be comma- or space-separated.

a (all)
All types of debugging output are enabled. This is equivalent to using ‘-d’.

b (basic)
Basic debugging prints each target that was found to be out-of-date, and whether the build was successful or not.

v (verbose)
A level above ‘basic’; includes messages about which makefiles were parsed, prerequisites that did not need to be rebuilt, etc. This option also enables ‘basic’ messages.

i (implicit)
Prints messages describing the implicit rule searches for each target. This option also enables ‘basic’ messages.

j (jobs)
Prints messages giving details on the invocation of specific subcommands.

m (makefile)
By default, the above messages are not enabled while trying to remake the makefiles. This option enables messages while rebuilding makefiles, too. Note that the ‘all’ option does enable this option. This option also enables ‘basic’ messages.

Another option is to use remake – a patched version of GNU Make that adds improved error reporting, the ability to trace execution, and a debugger.