Re: $< won't work

[Dave]

On Sat, 27 Jul 2002, Paul D. Smith wrote:

[snip]
> You're relying (or rather, the Xmame makefiles are relying) on
> non-portable make features.

An ongoing goal of my work with Frotz
(http://www.cs.csubak.edu/~dgriffi/proj/frotz/) is to make is as widely
and easily portable as possible.  This is why I want to be able to support
*BSD make and GNU make.

> See the GNU make manual section on "Missing Features and
> Incompatibilities", specifically this section:
> 
>    * In some Unix `make's, implicit rule search (*note Using Implicit
>      Rules: Implicit Rules.) is apparently done for _all_ targets, not
>      just those without commands.  This means you can do:
> 
>           foo.o:
>                   cc -c foo.c
> 
>      and Unix `make' will intuit that `foo.o' depends on `foo.c'.
> 
>      We feel that such usage is broken.  The prerequisite properties of
>      `make' are well-defined (for GNU `make', at least), and doing such
>      a thing simply does not fit the model.
> 
> In short, the Xmame makefile is expecting make to perform implicit rule
> searches _even if you give it an actual command script_, which is
> bizarre and not portable.

I see.  So in what I eventually copied from someone else's Makefile makes
explicit these rules?

> Since you gave it a command script, GNU make does not perform implicit
> rule searches, so it never finds an implicit rule saying that .o is
> built from .c, and thus there is no prerequisites for the .o files
> except those that you explicitly provide, and since you don't provide
> any the value of $< (and $^, etc.) will be empty.
> 
>   d> Sidenote: How about implementing local variables like .ALLSRC,
>   d> .TARGET, and so on?  (see *BSD make(1) manpage).
> 
> I don't have a copy of this manpage.  Is it available on the web?

See http://man.netbsd.org for manpages for manpages for NetBSD 1.3.3,
1.4.4, 1.5.3, 1.6A, and Redhat 7.0.

>   d> Someone posted a while ago about pursuading the FreeBSD people to
>   d> implement $> (a form which is implemented in NetBSD's make(1) but
>   d> not recommended).
> 
> This is trivial to work around in GNU make; if your makefiles require it
> just add a:
> 
>   > = ^
> 
> to your makefile, or in some "portability" makefile you include with the
> MAKEFILES environment variable or something.

I've found a solution that satisfies both NetBSD's make and GNU make;
adding the following to the end of the Makefile:

.SUFFIXES:
.SUFFIXES: .c .o .h

.c.o:
        $(CC) $(FLAGS) $(CFLAGS) -o $@ -c $<

I borrowed the above from Nitfol's Makefile.  I'm not sure if I should
bother trying to satisfy FreeBSD's make at this point right now.


-- 
David Griffith
address@hidden