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

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Date:   Wed, 26 Jul 2023 08:48:24 -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 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.

>  # 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?

Thanks,
Ian

> --
> 2.41.0.487.g6d72f3e995-goog
>