perf jevents: Autogenerate empty-pmu-events.c

empty-pmu-events.c exists so that builds may occur without python
being installed on a system. Manually updating empty-pmu-events.c to
be in sync with jevents.py is a pain, let's use jevents.py to generate
empty-pmu-events.c.

1) change jevents.py so that an arch and model of none cause
   generation of a pmu-events.c without any json. Add a SPDX and
   autogenerated warning to the start of the file.

2) change Build so that if a generated pmu-events.c for arch none and
   model none doesn't match empty-pmu-events.c the build fails with a
   cat of the differences. Update Makefile.perf to clean up the files
   used for this.

3) update empty-pmu-events.c to match the output of jevents.py with
   arch and mode of none.

Committer notes:

The firtst paragraph is confusing, so I asked and Ian further clarified:

 ---
The requirement for python hasn't changed.

Case 1: no python or NO_JEVENTS=1
Build happens using empty-pmu-events.c that is checked in, no python
is required.

Case 2: python
pmu-events.c is created by jevents.py (requiring python) and then built.
This change adds a step where the empty-pmu-events.c is created using
jevents.py and that file is diffed against the checked in version.

This stops the checked in empty-pmu-events.c diverging if changes are
made to jevents.py. If the diff causes the build to fail then you just
copy the diff empty-pmu-events.c over the checked in one.
 ---

Reviewed-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jing Zhang <renyu.zj@linux.alibaba.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Oliver Sang <oliver.sang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Philip Li <philip.li@intel.com>
Cc: Sandipan Das <sandipan.das@amd.com>
Cc: Weilin Wang <weilin.wang@intel.com>
Cc: Xu Yang <xu.yang_2@nxp.com>
Link: https://lore.kernel.org/r/20240730191744.3097329-3-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile.perf

@@ -1277,6 +1277,8 @@ clean:: $(LIBAPI)-clean $(LIBBPF)-clean $(LIBSUBCMD)-clean $(LIBSYMBOL)-clean $(
 		$(OUTPUT)util/intel-pt-decoder/inat-tables.c \
 		$(OUTPUT)tests/llvm-src-{base,kbuild,prologue,relocation}.c \
 		$(OUTPUT)pmu-events/pmu-events.c \
+		$(OUTPUT)pmu-events/test-empty-pmu-events.c \
+		$(OUTPUT)pmu-events/empty-pmu-events.log \
 		$(OUTPUT)pmu-events/metric_test.log \
 		$(OUTPUT)$(fadvise_advice_array) \
 		$(OUTPUT)$(fsconfig_arrays) \

tools/perf/pmu-events/Build

@@ -11,6 +11,8 @@ METRIC_TEST_PY	=  pmu-events/metric_test.py
 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
+TEST_EMPTY_PMU_EVENTS_C = $(OUTPUT)pmu-events/test-empty-pmu-events.c
+EMPTY_PMU_EVENTS_TEST_LOG = $(OUTPUT)pmu-events/empty-pmu-events.log
 
 ifeq ($(JEVENTS_ARCH),)
 JEVENTS_ARCH=$(SRCARCH)
@@ -31,7 +33,15 @@ $(METRIC_TEST_LOG): $(METRIC_TEST_PY) $(METRIC_PY)
 	$(call rule_mkdir)
 	$(Q)$(call echo-cmd,test)$(PYTHON) $< 2> $@ || (cat $@ && false)
 
-$(PMU_EVENTS_C): $(JSON) $(JSON_TEST) $(JEVENTS_PY) $(METRIC_PY) $(METRIC_TEST_LOG)
+$(TEST_EMPTY_PMU_EVENTS_C): $(JSON) $(JSON_TEST) $(JEVENTS_PY) $(METRIC_PY) $(METRIC_TEST_LOG)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $(JEVENTS_PY) none none pmu-events/arch $@
+
+$(EMPTY_PMU_EVENTS_TEST_LOG): $(EMPTY_PMU_EVENTS_C) $(TEST_EMPTY_PMU_EVENTS_C)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,test)diff -u $? 2> $@ || (cat $@ && false)
+
+$(PMU_EVENTS_C): $(JSON) $(JSON_TEST) $(JEVENTS_PY) $(METRIC_PY) $(METRIC_TEST_LOG) $(EMPTY_PMU_EVENTS_TEST_LOG)
 	$(call rule_mkdir)
 	$(Q)$(call echo-cmd,gen)$(PYTHON) $(JEVENTS_PY) $(JEVENTS_ARCH) $(JEVENTS_MODEL) pmu-events/arch $@
 endif

tools/perf/pmu-events/jevents.py

@@ -1256,6 +1256,10 @@ such as "arm/cortex-a34".''',
       'output_file', type=argparse.FileType('w', encoding='utf-8'), nargs='?', default=sys.stdout)
   _args = ap.parse_args()
 
+  _args.output_file.write(f"""
+/* SPDX-License-Identifier: GPL-2.0 */
+/* THIS FILE WAS AUTOGENERATED BY jevents.py arch={_args.arch} model={_args.model} ! */
+""")
   _args.output_file.write("""
 #include <pmu-events/pmu-events.h>
 #include "util/header.h"
@@ -1281,7 +1285,7 @@ struct pmu_table_entry {
     if item.name == _args.arch or _args.arch == 'all' or item.name == 'test':
       archs.append(item.name)
 
-  if len(archs) < 2:
+  if len(archs) < 2 and _args.arch != 'none':
     raise IOError(f'Missing architecture directory \'{_args.arch}\'')
 
   archs.sort()