Re: [patch/rfc] Generate makefile dependencies

[Daniel Jacobowitz <drow@false.org>]

On Mon, Mar 08, 2004 at 01:06:01PM -0500, Andrew Cagney wrote:
> >On Mon, Mar 08, 2004 at 11:24:20AM -0500, Andrew Cagney wrote:
> >
> >>>>>>>Date: Sun, 07 Mar 2004 19:35:34 -0500
> >>>>
> >>>>>>>>>From: Andrew Cagney <cagney@gnu.org>
> >>>>>>>>>
> >>>>>>>>>The attached, er, hack, modifies configure.in so that all the 
> >>>>>>Makefile
> >>>>>>>>>dependencies are generated during configure time:
> >>>>>>>>>
> >>>>>>>>>	defs_h = ...
> >>>>>>>>>	foo.o: foo.c $(defs_h)
> >>>>>>>>>
> >>>>>>>>>It exploits the fact that GDB's code base is very consistent in 
> >>>>>>its use
> >>>>>>>>>of "foo.h" vs <foo.h> -- the former is assumed to be local, the 
> >>>>>>latter
> >>>>>>>>>in a system library.
> >>>
> >>>>>
> >>>>>
> >>>>>Won't it be better to use "gcc -MM" when we compile with GCC?
> >>
> >>>
> >>>It would, except we can't assume GCC :-(.  Better to always use the sed 
> >>>script as that way we'll know it always (hopefully :-) works.
> >>>
> >>>It needs comments (and a doco update).
> >
> >
> >So what about using the output of gcc -MM (or one of the other -M
> >options?) to generate dependencies in the source directory, like BFD
> >does?
> 
> How is embedding this stuff in the source directory better?

Because it doesn't need to rely on assumptions about the GDB coding
style, and it doesn't require parsing all the source files when we
configure?  It's like regenerating configure; we try not to run
autoconf during the build process, and not just because autoconf is so
finicky.

> >BTW, your comment about running automake to update deps in BFD is
> >actually incorrect.  You run 'make dep-am', which IIRC seds Makefile.am
> >and maye regenerates Makefile.in; the dependencies aren't managed by
> >automake.  Recent versions of automake do have top-notch dependency
> >support though.
> 
> It appears to eventually run "gcc -MM" ... :-(

Sure.  The point (for the BFD method) is that dependencies are generated 
on a machine with GCC, which is not a hardship.  I don't know anything
about how automake handles this.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer