On Tue, Feb 14, 2017 at 09:50:20AM -0300, Arnaldo Carvalho de Melo wrote:

SNIP

What I think Ingo meant with dependency at the build system level is to
somehow state that if file A gets changed, then tool B must be rebuilt.

Now that samples/bpf and tools/perf/ depend on tools/lib/bpf/ I _always_
build both, ditto for tools/objtool, that shares a different library
with tools/perf/, tools/lib/subcmd/:

ENTRYPOINT make -C /git/linux/tools/perf O=/tmp/build/perf && \
           rm -rf /tmp/build/perf/{.[^.]*,*} && \
           make NO_LIBELF=1 -C /git/linux/tools/perf O=/tmp/build/perf && \
           make -C /git/linux/tools/objtool O=/tmp/build/objtool && \
           make -C /git/linux O=/tmp/build/linux allmodconfig && \
           make -C /git/linux O=/tmp/build/linux headers_install && \
           make -C /git/linux O=/tmp/build/linux samples/bpf/

This is the default action for my
docker.io/acmel/linux-perf-tools-build-fedora:rawhide container.

It is published, so a:

   docker pull docker.io/acmel/linux-perf-tools-build-fedora:rawhide

And then run it before pushing things upstream would catch these kinds
of errors.

But that would possibly disrupt too much people's workflow, that is why
using the Kbuild originated tools/build/ we have to somehow express that
when a change is made in a file then a tool that uses that file needs to
be rebuilt.

we already have the check in the check-headers.sh script,
an AFAICS there's no 'rebuild' option here.. just warn or fail
because the headers update needs to be done manualy

Makefile rules probably would be enough, but then it would have to be
done at the tools/build/ level and all tools using shared components
would have to use it to trigger the rebuild.

we can move/invoke the check-headers.sh script in some upper dir

jirka