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

[Namhyung Kim <namhyung@kernel.org>]

Hi Ian,

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.

Thanks,
Namhyung