kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 243 insertions, 0 deletions

diff --git a/tools/perf/pmu-events/Build b/tools/perf/pmu-events/Build
new file mode 100644
index 000000000..372773b99
--- /dev/null
+++ b/tools/perf/pmu-events/Build
@@ -0,0 +1,243 @@
+EMPTY_PMU_EVENTS_C = pmu-events/empty-pmu-events.c
+# pmu-events.c will be generated by jevents.py or copied from EMPTY_PMU_EVENTS_C
+PMU_EVENTS_C	=  $(OUTPUT)pmu-events/pmu-events.c
+PMU_EVENTS_STRING_C = $(OUTPUT)pmu-events/pmu-events-string.c
+
+pmu-events-y	+= pmu-events.o
+ifneq ($(NO_JEVENTS),1)
+pmu-events-y	+= pmu-events-string.o
+endif
+
+# pmu-events.c file is generated in the OUTPUT directory so it needs a
+# separate rule to depend on it properly
+$(OUTPUT)pmu-events/pmu-events.o: $(PMU_EVENTS_C)
+	$(call rule_mkdir)
+	$(call if_changed_dep,cc_o_c)
+
+$(OUTPUT)pmu-events/pmu-events-string.o: $(PMU_EVENTS_STRING_C)
+	$(call rule_mkdir)
+	$(call if_changed_dep,cc_o_c)
+
+# Message for $(call echo-cmd,cp), possibly remove the src file from
+# the destination to save space in the build log.
+quiet_cmd_cp   = COPY    $(patsubst %$<,%,$@) <- $<
+
+# --- NO_JEVENTS=1 build ---
+ifeq ($(NO_JEVENTS),1)
+$(PMU_EVENTS_C): $(EMPTY_PMU_EVENTS_C)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,cp)cp $< $@
+else
+# --- Regular build ---
+
+# Setup the JEVENTS_ARCH and JEVENTS_MODEL
+ifeq ($(JEVENTS_ARCH),)
+JEVENTS_ARCH=$(SRCARCH)
+endif
+JEVENTS_MODEL ?= all
+
+# The input json/csv files
+SRC_DIR		:= pmu-events/arch
+ifeq ($(JEVENTS_ARCH),all)
+SRC_JSON	:= $(shell find $(SRC_DIR) -name '*.json' -o -name '*.csv')
+else
+SRC_JSON	:= $(shell find $(SRC_DIR)/common $(SRC_DIR)/test $(SRC_DIR)/$(JEVENTS_ARCH) -name '*.json' -o -name '*.csv')
+endif
+
+# Python to build the generic legacy cache events
+LEGACY_CACHE_PY	=  pmu-events/make_legacy_cache.py
+LEGACY_CACHE_JSON = $(OUTPUT)pmu-events/arch/common/common/legacy-cache.json
+GEN_JSON = $(LEGACY_CACHE_JSON)
+
+$(LEGACY_CACHE_JSON): $(LEGACY_CACHE_PY)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $(LEGACY_CACHE_PY) > $@
+
+# Python to generate architectural metrics
+GEN_METRIC_DEPS := pmu-events/metric.py pmu-events/common_metrics.py
+# Functions to extract the model from an extra-metrics.json or extra-metricgroups.json path.
+model_name = $(notdir $(patsubst %/,%,$(dir $(1))))
+vendor_name = $(notdir $(patsubst %/,%,$(dir $(patsubst %/,%,$(dir $(1))))))
+
+ifeq ($(JEVENTS_ARCH),$(filter $(JEVENTS_ARCH),x86 all))
+# Generate AMD Json
+ZENS := $(shell ls -d pmu-events/arch/x86/amdzen*)
+ZEN_METRICS = $(foreach x,$(ZENS),$(OUTPUT)$(x)/extra-metrics.json)
+ZEN_METRICGROUPS = $(foreach x,$(ZENS),$(OUTPUT)$(x)/extra-metricgroups.json)
+GEN_JSON += $(ZEN_METRICS) $(ZEN_METRICGROUPS)
+
+$(ZEN_METRICS): pmu-events/amd_metrics.py $(GEN_METRIC_DEPS)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $< $(call model_name,$@) pmu-events/arch > $@
+
+$(ZEN_METRICGROUPS): pmu-events/amd_metrics.py $(GEN_METRIC_DEPS)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $< -metricgroups $(call model_name,$@) pmu-events/arch > $@
+
+endif
+
+ifeq ($(JEVENTS_ARCH),$(filter $(JEVENTS_ARCH),arm64 all))
+# Generate ARM Json
+ARMS := $(shell ls -d pmu-events/arch/arm64/arm/*|grep -v cmn)
+ARM_METRICS = $(foreach x,$(ARMS),$(OUTPUT)$(x)/extra-metrics.json)
+ARM_METRICGROUPS = $(foreach x,$(ARMS),$(OUTPUT)$(x)/extra-metricgroups.json)
+GEN_JSON += $(ARM_METRICS) $(ARM_METRICGROUPS)
+
+$(ARM_METRICS): pmu-events/arm64_metrics.py $(GEN_METRIC_DEPS)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $< $(call vendor_name,$@) $(call model_name,$@) pmu-events/arch > $@
+
+$(ARM_METRICGROUPS): pmu-events/arm64_metrics.py $(GEN_METRIC_DEPS)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $< -metricgroups $(call vendor_name,$@) $(call model_name,$@) pmu-events/arch > $@
+
+endif
+
+ifeq ($(JEVENTS_ARCH),$(filter $(JEVENTS_ARCH),x86 all))
+# Generate Intel Json
+INTELS := $(shell ls -d pmu-events/arch/x86/*|grep -v amdzen|grep -v mapfile.csv)
+INTEL_METRICS = $(foreach x,$(INTELS),$(OUTPUT)$(x)/extra-metrics.json)
+INTEL_METRICGROUPS = $(foreach x,$(INTELS),$(OUTPUT)$(x)/extra-metricgroups.json)
+GEN_JSON += $(INTEL_METRICS) $(INTEL_METRICGROUPS)
+
+$(INTEL_METRICS): pmu-events/intel_metrics.py $(GEN_METRIC_DEPS)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $< $(call model_name,$@) pmu-events/arch > $@
+
+$(INTEL_METRICGROUPS): pmu-events/intel_metrics.py $(GEN_METRIC_DEPS)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $< -metricgroups $(call model_name,$@) pmu-events/arch > $@
+
+endif
+
+OUT_DIR		:= $(OUTPUT)pmu-events/arch
+
+ifeq ($(OUTPUT),)
+OUT_JSON	:= $(SRC_JSON)
+ORPHAN_FILES	:=
+else
+# Things that need to be built in the OUTPUT directory. Note, ensure
+# there is a slash after the directory name so that it matches what
+# $(dir) gives in COPY_RULE.
+OUT_JSON	:= $(patsubst $(SRC_DIR)/%,$(OUT_DIR)/%,$(SRC_JSON))
+OUT_DIRS	:= $(sort $(patsubst %/,%,$(dir $(OUT_JSON))))
+
+# Things already in the OUTPUT directory
+CUR_OUT_JSON	:= $(shell [ -d $(OUT_DIR) ] && find $(OUT_DIR) -type f)
+
+# Things in the OUTPUT directory but shouldn't be there as computed by
+# OUT_JSON and GEN_JSON.
+
+ORPHAN_FILES	:= $(filter-out $(OUT_JSON) $(GEN_JSON),$(CUR_OUT_JSON))
+
+# Message for $(call echo-cmd,mkd). There is already a mkdir message
+# but it assumes $@ is a file to mkdir the directory for.
+quiet_cmd_mkd  = MKDIR   $@
+
+$(OUT_DIRS):
+	$(Q)$(call echo-cmd,mkd)mkdir -p $@
+
+# Explicitly generate rules to copy SRC_JSON files as $(dir) cannot
+# apply to $@ in a dependency. Exclude from the copy rules any that
+# look like they are copying generated json. This happens as a perf
+# build within the tools/perf directory will leave generated json
+# files within the tree, these then get picked up by SRC_JSON find.
+define COPY_RULE
+$(2): $(1) | $(3)
+	$$(Q)$$(call echo-cmd,cp)cp $(1) $(2)
+endef
+$(foreach src,$(SRC_JSON), \
+    $(eval dest := $(patsubst $(SRC_DIR)/%,$(OUT_DIR)/%,$(src))) \
+    $(eval ddir := $(patsubst %/,%,$(dir $(dest)))) \
+    $(if $(filter $(dest),$(GEN_JSON)),, \
+        $(eval $(call COPY_RULE,$(src),$(dest),$(ddir))) \
+    ) \
+)
+
+endif # ifneq ($(OUTPUT),)
+
+JEVENTS_PY	=  pmu-events/jevents.py
+METRIC_PY	=  pmu-events/metric.py
+
+# Rule to run the metric test.
+METRIC_TEST_PY	=  pmu-events/metric_test.py
+METRIC_TEST_LOG	=  $(OUTPUT)pmu-events/metric_test.log
+
+$(METRIC_TEST_LOG): $(METRIC_TEST_PY) $(METRIC_PY)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,test)$(PYTHON) $< 2> $@ || (cat $@ && false)
+
+# Rule to create then ensure the empty-pmu-events.c is in sync.
+TEST_EMPTY_PMU_EVENTS_C = $(OUTPUT)pmu-events/test-empty-pmu-events.c
+EMPTY_PMU_EVENTS_TEST_LOG = $(OUTPUT)pmu-events/empty-pmu-events.log
+
+$(TEST_EMPTY_PMU_EVENTS_C): $(OUT_JSON) $(GEN_JSON) $(JEVENTS_PY) $(METRIC_PY)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $(JEVENTS_PY) none none $(OUTPUT)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)
+
+
+# Dependencies for jevents.py
+JEVENTS_DEPS := $(OUT_JSON) $(GEN_JSON) $(JEVENTS_PY) $(METRIC_PY) $(EMPTY_PMU_EVENTS_TEST_LOG) $(METRIC_TEST_LOG)
+
+# Rules to run mypy if enabled.
+ifdef MYPY
+define MYPY_RULE
+$(2): $(1)
+	$$(Q)$$(call echo-cmd,test)mypy $(1) > $(2) || (cat $(2) && rm $(2) && false)
+endef
+$(foreach src,$(wildcard pmu-events/*.py), \
+    $(eval dest := $(patsubst pmu-events/%,$(OUTPUT)pmu-events/%.mypy_log,$(src))) \
+    $(eval $(call MYPY_RULE,$(src),$(dest))) \
+)
+
+MYPY_INPUTS := $(wildcard pmu-events/*.py)
+MYPY_OUTPUTS := $(patsubst pmu-events/%,$(OUTPUT)pmu-events/%.mypy_log,$(MYPY_INPUTS))
+JEVENTS_DEPS += $(MYPY_OUTPUTS)
+endif
+
+# Rules to run pylint if enabled.
+ifdef PYLINT
+define PYLINT_RULE
+$(2): $(1)
+	$$(Q)$$(call echo-cmd,test)pylint $(1) > $(2) || (cat $(2) && rm $(2) && false)
+endef
+$(foreach src,$(wildcard pmu-events/*.py), \
+    $(eval dest := $(patsubst pmu-events/%,$(OUTPUT)pmu-events/%.pylint_log,$(src))) \
+    $(eval $(call PYLINT_RULE,$(src),$(dest))) \
+)
+
+PYLINT_INPUTS := $(wildcard pmu-events/*.py)
+PYLINT_OUTPUTS := $(patsubst pmu-events/%,$(OUTPUT)pmu-events/%.pylint_log,$(PYLINT_INPUTS))
+JEVENTS_DEPS += $(PYLINT_OUTPUTS)
+endif
+
+# If there are orphaned files remove them.
+ifneq ($(strip $(ORPHAN_FILES)),)
+.PHONY: prune_orphans
+
+# Message for $(call echo-cmd,rm). Generally cleaning files isn't part
+# of a build step.
+quiet_cmd_rm = RM      ...$(words $^) orphan file(s)...
+
+# The list of files can be long. Use xargs to prevent issues.
+prune_orphans: $(ORPHAN_FILES)
+	$(Q)$(call echo-cmd,rm)echo "$^" | xargs rm -f
+
+JEVENTS_DEPS += prune_orphans
+endif
+
+# Finally, the rule to build pmu-events.c using jevents.py. All test
+# and inputs are dependencies.
+$(PMU_EVENTS_C): $(JEVENTS_DEPS)
+	$(call rule_mkdir)
+	$(Q)$(call echo-cmd,gen)$(PYTHON) $(JEVENTS_PY) $(JEVENTS_ARCH) $(JEVENTS_MODEL) \
+            $(OUT_DIR) $(PMU_EVENTS_C) $(PMU_EVENTS_STRING_C)
+
+$(PMU_EVENTS_STRING_C): $(PMU_EVENTS_C)
+	@:
+
+endif # ifeq ($(NO_JEVENTS),1)