eddieh/gnu-make-oddness.org

## gnu-make-oddness.org

      
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              gnu-make-oddness.org
            
          
    GNU Make Oddness

Since version 4.0 of GNU Make a feature was added that almost every
  makefile should use. The 4.0 release notes describes the feature as
  “setting the -r and -R options in MAKEFLAGS inside a makefile now
  works as expected, removing all builtin rules and variables,
  respectively.”
Unfortunately, despite the claim it does not work as expected. Maybe
  there’s some justification for the behavior, but it certainly isn’t
  expected.
Why set the make flags -r and -R? The Linux makefile explains it
  perfectly “Do not use make’s builtin rules and variables (this
  increases performance and avoids hard-to-debug behavior).”
For me personally, setting those flags makes the ever useful output of
  -p and -d less verbose and easier to read.
For this explainer I created two makefiles. Makefile.builtins and
  Makefile.nobuiltins:
Makefile.builtins
$(foreach v, $(.VARIABLES), $(info $(v)))
Makefile.nobuiltins
MAKEFLAGS += -rR
$(foreach v, $(.VARIABLES), $(info $(v)))
Each makefile will print a list of defined variables names. We can
  easily count how many variables each makefile has defined by piping to
  wc.
$ make -f Makefile.builtins | wc -l
make: *** No targets.  Stop.
   107
This invocation is showing 107 defined variables. This number includes
  variables inherited from the environment, which is around 10
  variables in the chroot environment I’m using. So make has around 97
  builtin variables. So how many variables does the second makefile have
  defined?
make -f Makefile.nobuiltins | wc -l
make: *** No targets.  Stop.
     107
I told you the behavior isn’t as expected.
To prove the behavior of -rR on the command line isn’t the same as
  setting MAKEFLAGS consider the next invocation:
make -f Makefile.builtins -rR | wc -l
make: *** No targets.  Stop.
      44
Why isn’t it 0 (or 10 counting the inherited variable from the
  environment)? That’s because make needs a few variables to be around no
  matter what.
Those variables as far as I can tell are:
.DEFAULT_GOAL
.FEATURES
.LOADED
.RECIPEPREFIX
.SHELLFLAGS
.VARIABLES
CURDIR
GNUMAKEFLAGS
MAKE
MAKEFILES
MAKEFILE_LIST
MAKEFLAGS
MAKELEVEL
MAKE_COMMAND
MAKE_HOST
MAKE_TERMERR
MAKE_VERSION
MFLAGS
SHELL
SUFFIXES

and the cryptic variables %D %F *D *F +D +F <D <F ?D ?F @D @F ^D ^F