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Date:   Thu, 27 Jul 2023 08:31:52 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Namhyung Kim <namhyung@kernel.org>
Cc:     Ian Rogers <irogers@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-perf-users@vger.kernel.org,
        Anup Sharma <anupnewsmail@gmail.com>, stable@vger.kernel.org
Subject: Re: [PATCH 1/2] perf build: Update build rule for generated files
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Em Wed, Jul 26, 2023 at 11:45:44PM -0700, Namhyung Kim escreveu:
> On Wed, Jul 26, 2023 at 9:48 PM Ian Rogers <irogers@google.com> wrote:
> > On Wed, Jul 26, 2023 at 6:01 PM Namhyung Kim <namhyung@kernel.org> wrote:
> > > On Wed, Jul 26, 2023 at 5:36 PM Ian Rogers <irogers@google.com> wrote:
> > > > On Wed, Jul 26, 2023 at 3:57 PM Namhyung Kim <namhyung@kernel.org> wrote:
> > > > > On Wed, Jul 26, 2023 at 8:48 AM Ian Rogers <irogers@google.com> wrote:
> > > > > > On Wed, Jul 26, 2023 at 6:36 AM Namhyung Kim <namhyung@kernel.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@vger.kernel.org
> > > > > > > Signed-off-by: Namhyung Kim <namhyung@kernel.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)
> > > > ```
> > >
> > > Probably, but I wonder if it affects the normal .c files expecting
> > > them in the OUTPUT directory.
> >
> > Hmm.. I think the longer matches may be necessary to trigger the "more
> > specific" ordering:
> > https://www.gnu.org/software/make/manual/html_node/Pattern-Match.html
> >
> > I'm not keen on these extra rules that mirror existing rules, it is a
> > bit cryptic what is going on. I wonder if it would be cleaner just to
> > fail the build if the bogus pmu-events.c exists. For example:
> 
> I prefer just making it build instead of failing.  But not strongly
> against your idea.  It'd be nice to hear what others think.. Arnaldo?

I think that we should just ignore any build files in the source tree
when using 'O=', i.e.:

make -C tools/perf

genereated files (in the source tree) should not be used when, right
after running it, we run:

make -C tools/perf O=/some/build/dir

If we run 'make -C tools/perf' and there is a pmu-events.c, use it if
its timestamp is more recent than the files from which it was generated,
as usual for a make managed build.

- Arnaldo
 
> > ```
> > --- a/tools/perf/pmu-events/Build
> > +++ b/tools/perf/pmu-events/Build
> > @@ -12,6 +12,14 @@ EMPTY_PMU_EVENTS_C = pmu-events/empty-pmu-events.c
> > PMU_EVENTS_C   =  $(OUTPUT)pmu-events/pmu-events.c
> > METRIC_TEST_LOG        =  $(OUTPUT)pmu-events/metric_test.log
> >
> > +ifneq ($(OUTPUT),)
> > +ifneq ($(wildcard pmu-events/pmu-events.c),)
> > +dummy := $(error OUTPUT set but tools/perf/pmu-events/pmu-events.c exists. \
> > +           This can mean the generated version of pmu-events.c is not
> > compiled. \
> > +           Try 'cd tools/perf; make clean; cd -' and then rebuilding.)
> 
> I've tested this and this message is buried in the stream of
> parallel build outputs. :(
> 
> Thanks,
> Namhyung
> 
> 
> > +endif
> > +endif
> > +
> > ifeq ($(JEVENTS_ARCH),)
> > JEVENTS_ARCH=$(SRCARCH)
> > endif
> > ```

-- 

- Arnaldo