Paul Smith via austin-group-l at The Open Group <austin-group-l@opengroup.org>
wrote:
> On Thu, 2020-11-05 at 09:25 +0000, Geoff Clare via austin-group-l at
> The Open Group wrote:
> > That doesn't make any difference, since .c and .o are both in the
> > specified suffixes, so that brings the default .c.o rule into play.
>
> Hm. Right, I forgot that clearing the suffixes doesn't also delete the
> rules. It's annoying that there's no POSIX way to delete the default
> rules from within the makefile.
There is no need to do that.
In former times, there was no way to clear .SUFFIXES, but at that time, SunOS
defined default rules that look this way:
SUFFIXES= .o .c ...
.SUFFIXES: $(SUFFIXES)
so you could clear it by overwriting the SUFFIXES variable from your user
makefile.
Now POSIX requires that writing:
.SUFFIXES:
into a Makefile clears the suffix list and thus effectively disables all default
implicit rules.
If you only like the .c.o rule but are not happy with the builtin default rule
for e.g. .c.o:, you can overwrite it by e.g. writing:
.SUFFIXES:
.SUFFIXES: .o .c
.c.o:
echo foo
In other words, a users makefile has full control over the "builtin" default
rules even without a need to use "make -r".
> In my opinion the -r option is wrong. Whether or not the default rules
> should be used is a function of the _makefile_, not a function of the
> _user_ of the makefile (the person who runs make). If the makefile is
> written so that it doesn't want or need the default rules then the
> makefile should be able to delete them. It shouldn't be up to the
> invoker of make to do that.
Well GNU make makes the mistake to define pattern matching implicit rules in
its default rules and this causes the following problems:
- pattern matching rules have precedence over suffix rules and may
themselves not be overwritten
- pattern matching rules match in the order of their apperance to the
parser. The first pattern rule that matches a specific pattern is
used. Later specifying a replacement rule for a specific pattern is
impossible.
- The built in default rules must to be "read" by make before the users
makefiles are parsed in order to allow them (the suffix rules) to be
overwritten. Any pattern matching rule that appears in the builtin
default rules thus would have precedence over anything else and cannot
be overwritten.
For this reason, SunPro Make intentionally does not make use of pattern
matching rules in the builtin default rules in order to permit the user to
have full control over the behavior of make without a need to call "make -r".
Jörg
--
EMail:jo...@schily.net (home) Jörg Schilling D-13353 Berlin
Blog: http://schily.blogspot.com/
URL: http://cdrecord.org/private/ http://sf.net/projects/schilytools/files/'
