Re: make capabilities

[jtc at redback dot com (J.T. Conklin)]

>>>>> "Eli" == Eli Zaretskii <eliz@is.elta.co.il> writes:
>> Is it safe to assume that all versions of make used to build GDB will
>> understand the ${FOO:.c=.o} construct?  It does not appear to be used
>> elsewhere in the GDB or binutils trees, so it is possible (maybe even
>> likely) that they do not.  But I do not know how to solve a problem
>> without it.
>> 
>> The problem is the "lint" target:
>> 
>> lint:   $(LINTFILES)
>> $(LINT) $(INCLUDE_CFLAGS) $(LINTFLAGS) $(LINTFILES) \
>> `echo $(DEPFILES) | sed 's/\.o /\.c /g'`
>> 
>> If srcdir != objdir, lint is not able to find the source files.  This
>> can be fixed if the rule is re-written as such:
>> 
>> lint:   $(LINTFILES) $(DEPFILES:.c=.o)
>> $(LINT) $(INCLUDE_CFLAGS) $(LINTFLAGS) $^
>> 
>> Thoughts?

Eli>   1. The current Emacs distribution uses $(FOO:.x=.y) in its Makefile's.  
Eli>      While this version is not yet released, its pretest was tested on 
Eli>      many different systems, and none failed to build it.

Good to hear.  I'd feel more comfortable if it had been released and there
weren't any recorded complaints.

Eli>   2. However, it _is_ known that not all versions of Make support that 
Eli>      construct.  If you want to be 100% portable, you can edit .c into .o 
Eli>      with `sed` invocation in the rule's commands.

It gets a little tricky if the transformation occurs in the rule's
commands instead of in the dependencies.  If it's not done in the
dependencies, $^ expands to something like:

    ... $(srcdir)/values.c i386-tdep.o i387-tdep.o ...

The sed rule would have to prepend $(srcdir)/ to each file it changes
.o to .c.  Not complicated, but it might be a bit confusing.


Given the above two points, I think I'll take emacs' lead and use
$(FOO:.x=.y), but will be prepared to change it to use sed if the
need arises.  Not many people will be using the lint target anyway.

I also found that $^ is not supported in all makes, so $? will have to
be used instead.  It should work fine, as long as there is no file
named lint.  We can add a .PHONY directive to ensure that gmake will
get it right regardless.

        --jtc

-- 
J.T. Conklin
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