Re: [PATCH bpf-next v3 2/7] tools/bpftool: Force clean of out-of-tree build

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Wed, Nov 11, 2020 at 12:55 AM Jean-Philippe Brucker
<jean-philippe@linaro.org> wrote:
>
> On Tue, Nov 10, 2020 at 08:57:51PM -0800, Andrii Nakryiko wrote:
> > On Tue, Nov 10, 2020 at 8:46 AM Jean-Philippe Brucker
> > <jean-philippe@linaro.org> wrote:
> > >
> > > Cleaning a partial build can fail if the output directory for libbpf
> > > wasn't created:
> > >
> > > $ make -C tools/bpf/bpftool O=/tmp/bpf clean
> > > /bin/sh: line 0: cd: /tmp/bpf/libbpf/: No such file or directory
> > > tools/scripts/Makefile.include:17: *** output directory "/tmp/bpf/libbpf/" does not exist.  Stop.
> > > make: *** [Makefile:36: /tmp/bpf/libbpf/libbpf.a-clean] Error 2
> > >
> > > As a result make never gets around to clearing the leftover objects. Add
> > > the libbpf output directory as clean dependency to ensure clean always
> > > succeeds (similarly to the "descend" macro). The directory is later
> > > removed by the clean recipe.
> > >
> > > Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > > ---
> > >  tools/bpf/bpftool/Makefile | 8 +++++---
> > >  1 file changed, 5 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> > > index f60e6ad3a1df..1358c093b812 100644
> > > --- a/tools/bpf/bpftool/Makefile
> > > +++ b/tools/bpf/bpftool/Makefile
> > > @@ -27,11 +27,13 @@ LIBBPF = $(LIBBPF_PATH)libbpf.a
> > >
> > >  BPFTOOL_VERSION ?= $(shell make -rR --no-print-directory -sC ../../.. kernelversion)
> > >
> > > -$(LIBBPF): FORCE
> > > -       $(if $(LIBBPF_OUTPUT),@mkdir -p $(LIBBPF_OUTPUT))
> > > +$(LIBBPF_OUTPUT):
> > > +       $(QUIET_MKDIR)mkdir -p $@
> > > +
> > > +$(LIBBPF): FORCE | $(LIBBPF_OUTPUT)
> > >         $(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_OUTPUT) $(LIBBPF_OUTPUT)libbpf.a
> > >
> > > -$(LIBBPF)-clean:
> > > +$(LIBBPF)-clean: $(LIBBPF_OUTPUT)
> >
> > shouldn't this be `| $(LIBBPF_OUTPUT)` ?
>
> It wouldn't have any effect here. Order-only prerequisites tell make to
> only build the prerequisite before the target, but not to update the
> target if the prerequisite was updated. Because $(LIBBPF)-clean is not a
> file, the recipe is always run and adding the | doesn't make a difference.

I know. I wanted it just for consistency, because everything after |
means "make sure it's completed, but it's not my direct input". But
I'm ok either way, it's not that important. Also $(LIBBPF)-clean and
$(LIBBPF_BOOTSTRAP)-clean should be .PHONY targets, but then again in
practice won't matter, because unlikely that we'll have such files.
Would be nice to follow up with a fix, but I'll apply your patch set
as is.

>
> Thanks,
> Jean