linux-kernel - Re: [PATCH 1/2] perf build: Update build rule for generated files

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Date:   Wed, 26 Jul 2023 17:36:24 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-perf-users@...r.kernel.org,
        Anup Sharma <anupnewsmail@...il.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] perf build: Update build rule for generated files

On Wed, Jul 26, 2023 at 3:57 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Hi Ian,
>
> On Wed, Jul 26, 2023 at 8:48 AM Ian Rogers <irogers@...gle.com> wrote:
> >
> > On Wed, Jul 26, 2023 at 6:36 AM Namhyung Kim <namhyung@...nel.org> wrote:
> > >
> > > The bison and flex generate C files from the source (.y and .l)
> > > files.  When O= option is used, they are saved in a separate directory
> > > but the default build rule assumes the .C files are in the source
> > > directory.  So it might read invalid file if there are generated files
> > > from an old version.  The same is true for the pmu-events files.
> > >
> > > For example, the following command would cause a build failure:
> > >
> > >   $ git checkout v6.3
> > >   $ make -C tools/perf  # build in the same directory
> > >
> > >   $ git checkout v6.5-rc2
> > >   $ mkdir build  # create a build directory
> > >   $ make -C tools/perf O=build  # build in a different directory but it
> > >                                 # refers files in the source directory
> > >
> > > Let's update the build rule to specify those cases explicitly to depend
> > > on the files in the output directory.
> > >
> > > Note that it's not a complete fix and it needs the next patch for the
> > > include path too.
> > >
> > > Fixes: 80eeb67fe577 ("perf jevents: Program to convert JSON file")
> > > Cc: stable@...r.kernel.org
> > > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> > > ---
> > >  tools/build/Makefile.build  | 8 ++++++++
> > >  tools/perf/pmu-events/Build | 4 ++++
> > >  2 files changed, 12 insertions(+)
> > >
> > > diff --git a/tools/build/Makefile.build b/tools/build/Makefile.build
> > > index 89430338a3d9..f9396696fcbf 100644
> > > --- a/tools/build/Makefile.build
> > > +++ b/tools/build/Makefile.build
> > > @@ -117,6 +117,14 @@ $(OUTPUT)%.s: %.c FORCE
> > >         $(call rule_mkdir)
> > >         $(call if_changed_dep,cc_s_c)
> > >
> > > +$(OUTPUT)%-bison.o: $(OUTPUT)%-bison.c FORCE
> > > +       $(call rule_mkdir)
> > > +       $(call if_changed_dep,$(host)cc_o_c)
> > > +
> > > +$(OUTPUT)%-flex.o: $(OUTPUT)%-flex.c FORCE
> > > +       $(call rule_mkdir)
> > > +       $(call if_changed_dep,$(host)cc_o_c)
> > > +
> >
> > Hi Namhyung,
> >
> > as we have:
> > ```
> > $(OUTPUT)%.o: %.c FORCE
> >        $(call rule_mkdir)
> >        $(call if_changed_dep,$(host)cc_o_c)
> > ```
> > I'm not sure what the 2 additional rules achieve.
>
> The above rule assumes the .c files are in the source directory
> (without $(OUTPUT) prefix).  It caused a trouble when the
> flex and bison files are generated in the output directory and
> you have an old version of them in the source directory.
>
>
> >
> > >  # Gather build data:
> > >  #   obj-y        - list of build objects
> > >  #   subdir-y     - list of directories to nest
> > > diff --git a/tools/perf/pmu-events/Build b/tools/perf/pmu-events/Build
> > > index 150765f2baee..f38a27765604 100644
> > > --- a/tools/perf/pmu-events/Build
> > > +++ b/tools/perf/pmu-events/Build
> > > @@ -35,3 +35,7 @@ $(PMU_EVENTS_C): $(JSON) $(JSON_TEST) $(JEVENTS_PY) $(METRIC_PY) $(METRIC_TEST_L
> > >         $(call rule_mkdir)
> > >         $(Q)$(call echo-cmd,gen)$(PYTHON) $(JEVENTS_PY) $(JEVENTS_ARCH) $(JEVENTS_MODEL) pmu-events/arch $@
> > >  endif
> > > +
> > > +$(OUTPUT)pmu-events/pmu-events.o: $(PMU_EVENTS_C)
> > > +       $(call rule_mkdir)
> > > +       $(call if_changed_dep,$(host)cc_o_c)
> >
> > If we add this, do the Makefile.build changes still need to happen?
>
> The Makefile.build changes are specific to flex and bison files.
> So yes, we need this for pmu-events.c to work properly with O=
> option.

Got it, you are right I was confusing the flex/bison with the jevents
case. Can we get away with a single rule then:
```
 $(OUTPUT)%.o:  $(OUTPUT)%.c FORCE
        $(call rule_mkdir)
        $(call if_changed_dep,$(host)cc_o_c)
```

Thanks,
Ian

> Thanks,
> Namhyung