Re: Problem using -R in MAKEFLAGS

[Colm Aengus Murphy]

Hi John,

I tried using ".SUFFIXES:".
Its a lot better but it still doesn't stop all of the built in rules.

For the simple makefile:
.SUFFIXES:   

%.exe : %.c
   gcc -o $(@F) $<

I still get:
 Considering target file `helloworld.c'.
  Looking for an implicit rule for `helloworld.c'.
  Trying pattern rule with stem `helloworld'.
  Trying implicit prerequisite `helloworld.w'.
  Trying pattern rule with stem `helloworld.c'.
  Trying implicit prerequisite `helloworld.c,v'.
  Trying pattern rule with stem `helloworld.c'.
  Trying implicit prerequisite `RCS/helloworld.c,v'.
  Trying pattern rule with stem `helloworld.c'.
  Trying implicit prerequisite `RCS/helloworld.c'.
  Trying pattern rule with stem `helloworld.c'.
  Trying implicit prerequisite `s.helloworld.c'.
  Trying pattern rule with stem `helloworld.c'.
  Trying implicit prerequisite `SCCS/s.helloworld.c'.
  Trying pattern rule with stem `helloworld'.
  Trying implicit prerequisite `helloworld.w'.
  Looking for a rule with intermediate file `helloworld.w'.
   Avoiding implicit rule recursion.
   Trying pattern rule with stem `helloworld.w'.
   Trying implicit prerequisite `helloworld.w,v'.
   Trying pattern rule with stem `helloworld.w'.
   Trying implicit prerequisite `RCS/helloworld.w,v'.
   Trying pattern rule with stem `helloworld.w'.
   Trying implicit prerequisite `RCS/helloworld.w'.
   Trying pattern rule with stem `helloworld.w'.
   Trying implicit prerequisite `s.helloworld.w'.
   Trying pattern rule with stem `helloworld.w'.
   Trying implicit prerequisite `SCCS/s.helloworld.w'.
  No implicit rule found for `helloworld.c'.
  Finished prerequisites of target file `helloworld.c'.
 No need to remake target `helloworld.c'.

Regards

Colm A

John Graham-Cumming wrote:
> Philip Guenther wrote:
> > You can't affect how make processes a makefile by setting MAKEFLAGS in
> > the makefile itself.  Currently, make sets all the built-in variables
> > and rules before parsing the makefile, and that can be tested by the
> > makefile itself, so changing it would create all sorts of problems.
>
> That's not actually totally true.  Page 50 of the GNU Make manual 
> states: 'You can also set MAKEFLAGS in a makefile, to specify 
> additional flags that should be in effect for that makefile.'
>
> For example,
>
>     MAKEFLAGS += -n
>
>     .PHONY: all
>     all:
>         @echo Doing all
>
> will print 'echo Doing all' because the -n is in effect for that 
> Makefile.  Unfortunately, as you do state, there are some flags that 
> will not work when MAKEFLAGS is set inside a Makefile.  The source of 
> GNU Make shows that MAKEFLAGS is actually parsed twice: once before 
> handling the Makefile and once after:
>
>   /* Decode switches again, in case the variables were set by the 
> makefile.  */
>   decode_env_switches (STRING_SIZE_TUPLE ("MAKEFLAGS"));
>
> The flag you want to set for no built in rules is -r (note that the 
> original message errorneously talked about -R which is for built in 
> variables although it does force -r).  This translates to the 
> no_builtin_rules_flag variable in GNU Make's source.
>
> Unfortunately, this flag is used to control the setting up of the 
> built in rules BEFORE the Makefiles are parsed (as you state) and 
> hence you can't add -r to MAKEFLAGS in a Makefile and have it affect 
> that Makefile.  This is done so that new rules in the Makefile can 
> override the default rules as necessary.
>
> Most of the command-line switches will work if specified in MAKEFLAGS 
> in the Makefile and affect that Makefile (you can try out silly 
> examples like -v and -p to see the effect).
>
> Now, to actually solve your problem (disabling default rules in a 
> Makefile), there's a simple technique: you clear the default suffix 
> list for built-in rules.  This will prevent any of the built-in rules 
> from being searched and you can go ahead and define your own pattern 
> rules.
>
> So simply write:
>
>     .SUFFIXES:
>
> in the Makefile where you want to disable built-in rules.  This won't 
> kill the built-in variables, but they are probably less of a worry.
>
> John.

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Colm Aengus Murphy,                Tel       : +353 1 2911000
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Silicon & Software Systems,        Fax       : +353 1 2911001
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