Re: Make 4.3 rebuilds .o files when unnecessary

[Paul Smith]

On Wed, 2020-11-18 at 16:38 +0100, Tommaso Fonda wrote:
> When using make 4.3, as packaged in OpenSUSE Tumbleweed and Ubuntu
> 20.10, running "make" always rebuilds the whole kernel tree, even
> when no files have changed since the last time I completed a build.
> As soon as I roll back to make 4.2, the behaviour goes back to
> normal. Is this a bug?

Well, since it's not the behavior you want there's clearly a bug
SOMEWHERE.  If what you mean is it a bug in GNU make, there's no way we
can know that based on the info provided.  It could also be a bug in
your makefiles, that just happened to work OK for older versions of GNU
make.

Unfortunately I don't have the resources to check out your source tree
and try to reproduce it, so someone else will have to do some
investigation to narrow down the problem. 

The best way to do that is first, reduce the problem as much as
possible; for example see if you can pass arguments to make so that it
builds just one object file (the equivalent of "make foo.o" for
example), where when you run that make command it doesn't rebuild with
4.2 but always rebuilds with 4.3.

Then, run that command adding the --trace option to make and it should
show you information on why it decided to rebuild.  You can compare
that between the 4.2 and 4.3 releases, and if it's not clear what the
problem is please feel free to ask here again.