linux-kernel - [PATCH] perf jevents: Handle deleted JSONS in out of source builds

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Message-Id: <20260120-james-perf-json-delete-fix-v1-1-bae2194b1dcf@linaro.org>
Date: Tue, 20 Jan 2026 15:38:19 +0000
From: James Clark <james.clark@...aro.org>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
 Arnaldo Carvalho de Melo <acme@...nel.org>, 
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, 
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>, 
 Adrian Hunter <adrian.hunter@...el.com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Mark Brown <broonie@...nel.org>, James Clark <james.clark@...aro.org>
Subject: [PATCH] perf jevents: Handle deleted JSONS in out of source builds

The cp command here doesn't remove files that have been removed from the
sourcetree. That means incremental builds can either succeed with stale
events or will fail completely if a stale json file has a broken
reference in it.

Fix it by using rsync instead of cp. legacy-cache.json has to be
excluded as this is a generated file isn't present in the source tree.

This only happens when deleting a JSON file, which has only happened
once since the linked commit. The fixes commit is marked as the origin
of the problem in case any future changes that delete JSONs are back
ported, rather than the first commit that deleted a JSON file.

Reported-by: Mark Brown <broonie@...nel.org>
Closes: https://lore.kernel.org/linux-next/aW5XSAo88_LBPSYI@sirena.org.uk/
Fixes: 4bb55de4ff03 ("perf jevents: Support copying the source json files to OUTPUT")
Signed-off-by: James Clark <james.clark@...aro.org>
---
This is a bit of a hack and I thought that making jevents.py handle
multiple input folders would be a much better solution than this. Then
we could have "gen-pmu-events" for only generated files and "pmu-events"
for only in-tree input files. It would be very clear what's generated
and what's not and all copying rules and special clean rules just
disappear (and this isn't the first time these rules have caused build
issues).

Unfortunately, after a while of trying to modify the script I thought it
was too invasive for now. The script does output per-file at the very
bottom of the logic in process_one_file(), so adding files in another
folder ends up re-emitting section headers when another chunk is output.
Although other parts of the script do build things up in memory before
outputting so it was possible to make those parts work with multiple
folders transparently.
---
 tools/perf/pmu-events/Build | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/tools/perf/pmu-events/Build b/tools/perf/pmu-events/Build
index a46ab7b612df..079d04c4f7d8 100644
--- a/tools/perf/pmu-events/Build
+++ b/tools/perf/pmu-events/Build
@@ -12,13 +12,16 @@ 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
 LEGACY_CACHE_PY	=  pmu-events/make_legacy_cache.py
-LEGACY_CACHE_JSON = $(OUTPUT)pmu-events/arch/common/common/legacy-cache.json
+LEGACY_CACHE_SYNC_PATH = arch/common/common/legacy-cache.json
+LEGACY_CACHE_JSON = $(OUTPUT)pmu-events/$(LEGACY_CACHE_SYNC_PATH)
 
 ifeq ($(JEVENTS_ARCH),)
 JEVENTS_ARCH=$(SRCARCH)
 endif
 JEVENTS_MODEL ?= all
 
+GEN_JSON = $(patsubst %,$(OUTPUT)%,$(JSON)) $(LEGACY_CACHE_JSON)
+
 #
 # Locate/process JSON files in pmu-events/arch/
 # directory and create tables in pmu-events.c.
@@ -31,17 +34,20 @@ $(PMU_EVENTS_C): $(EMPTY_PMU_EVENTS_C)
 else
 # Copy checked-in json to OUTPUT for generation if it's an out of source build
 ifneq ($(OUTPUT),)
-$(OUTPUT)pmu-events/arch/%: pmu-events/arch/%
+SYNC_PMU_EVENTS := $(OUTPUT)pmu-events/.synced
+$(SYNC_PMU_EVENTS): $(JSON)
 	$(call rule_mkdir)
-	$(Q)$(call echo-cmd,gen)cp $< $@
+	$(Q)$(call echo-cmd,gen)rsync -a --delete --exclude=$(LEGACY_CACHE_SYNC_PATH) \
+		--include="*.json" --include="*.csv" pmu-events/arch $(OUTPUT)pmu-events/
+	$(Q)touch $@
+
+$(GEN_JSON): $(SYNC_PMU_EVENTS)
 endif
 
 $(LEGACY_CACHE_JSON): $(LEGACY_CACHE_PY)
 	$(call rule_mkdir)
 	$(Q)$(call echo-cmd,gen)$(PYTHON) $(LEGACY_CACHE_PY) > $@
 
-GEN_JSON = $(patsubst %,$(OUTPUT)%,$(JSON)) $(LEGACY_CACHE_JSON)
-
 $(METRIC_TEST_LOG): $(METRIC_TEST_PY) $(METRIC_PY)
 	$(call rule_mkdir)
 	$(Q)$(call echo-cmd,test)$(PYTHON) $< 2> $@ || (cat $@ && false)

---
base-commit: 571d29baa07e83e637075239f379f91353c24ec9
change-id: 20260120-james-perf-json-delete-fix-71553b379e8e

Best regards,
-- 
James Clark <james.clark@...aro.org>