Re: toolchain/60435: "make depend" is too fussy

The following reply was made to PR toolchain/60435; it has been noted by GNATS.

From: Robert Elz <[email protected]>
To: [email protected]
Cc: 
Subject: Re: toolchain/60435: "make depend" is too fussy
Date: Sat, 11 Jul 2026 03:08:12 +0700

     Date:        Fri, 10 Jul 2026 19:00:02 +0000 (UTC)
     From:        "Taylor R Campbell via gnats" <[email protected]>
     Message-ID:  <[email protected]>
 
   |  The transitive dependencies of b.h may not affect the _first_ build of
   |  a.o, but they will affect _subsequent_ builds of a.o.
 
 Yes, I know.
 
   |  We could use `cc -M -MF $*.d' in the .o rule in order to regenerate
   |  the .d file at the same time, but we don't.
 
 That's the kind of thing I am requesting, it was a change request, not
 a bug to be fixed.   If a dependency has changed, regenerate the list of
 dependencies, as well as the object.
 
   |  It also wouldn't help if a.c includes b.h and b.h includes c.h and
   |  _both_ b.h and c.h have to be generated.
 
 That's an unlikely case, generated files don't often include others (that
 also need generating), they can just generate everything into the one file
 (they are ephemeral after all) - c.h would (if it had some other use) still
 get generated, but would be included in b.h as content, not as a dependency).
 In the extreme case where that isn't possible, then we would need explicit
 rules in the makefile to make the right thing happen, but I doubt we'd need
 those very much.
 
   |  (Note that we would need that _in addition to_ a more lenient
   |  mkdep(1), or else the makefile would still not know that it has to
   |  generate b.h before it can compile a.c -> a.o.)
 
 If a.o depends upon b.h then that's make's whole reason for existing
 isn't it?   b.h must be up to date before a.o can be built.   Make knows
 that a.o depende upon b.h because a.c has a #include "b.h" in it, and
 we have run "make depend" (whether or not b.h actually exists at the time).
 
 
 While I am here, I expect that you (and others) have seem that the sparc,
 sparc64, and ia64 builds have been broken since I added the changes for
 the new user.* sysctl vars, as that's where an include file like this was
 needed.   Everything else builds with the
 
 	sysctl.d: user-version.h
 
 dependency that was the last of that set of changes, which made all the other
 builds work.   That include file needs to be generated (it contains the build
 date/time, so it gets regenerated every time a build is done).   For some
 reason this isn't working on sparc sparc64 or ia64, and at the minute I have
 no idea why.  I can reproduce it in a sparc build here - the file is never
 generated there.
 
 I am still looking, but the build system really is not my area, I have almost
 no idea how any of it works (I could handle 7th edition make just fine, but
 not what that has turned into).   So if anyone has any ideas, please either
 implement them, or send me suggestions.   The relevant Makefile is
 src/lib/libc/gen/Makefile.inc
 
 kre
 
 ps: the atari build is also broken, has been for a while, but that one is
 just the normal floppy filesystem overflow that happens ...