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, 355 insertions, 0 deletions

diff --git a/tools/perf/util/stat-shadow.c b/tools/perf/util/stat-shadow.c
new file mode 100644
index 000000000..c17373bb0
--- /dev/null
+++ b/tools/perf/util/stat-shadow.c
@@ -0,0 +1,355 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <errno.h>
+#include <math.h>
+#include <stdio.h>
+#include "evsel.h"
+#include "stat.h"
+#include "color.h"
+#include "debug.h"
+#include "pmu.h"
+#include "rblist.h"
+#include "evlist.h"
+#include "expr.h"
+#include "metricgroup.h"
+#include "cgroup.h"
+#include "units.h"
+#include "iostat.h"
+#include "util/hashmap.h"
+#include "tool_pmu.h"
+
+static bool tool_pmu__is_time_event(const struct perf_stat_config *config,
+				   const struct evsel *evsel, int *tool_aggr_idx)
+{
+	enum tool_pmu_event event = evsel__tool_event(evsel);
+	int aggr_idx;
+
+	if (event != TOOL_PMU__EVENT_DURATION_TIME &&
+	    event != TOOL_PMU__EVENT_USER_TIME &&
+	    event != TOOL_PMU__EVENT_SYSTEM_TIME)
+		return false;
+
+	if (config) {
+		cpu_aggr_map__for_each_idx(aggr_idx, config->aggr_map) {
+			if (config->aggr_map->map[aggr_idx].cpu.cpu == 0) {
+				*tool_aggr_idx = aggr_idx;
+				return true;
+			}
+		}
+		pr_debug("Unexpected CPU0 missing in aggregation for tool event.\n");
+	}
+	*tool_aggr_idx = 0; /* Assume the first aggregation index works. */
+	return true;
+}
+
+static int prepare_metric(struct perf_stat_config *config,
+			  const struct metric_expr *mexp,
+			  const struct evsel *evsel,
+			  struct expr_parse_ctx *pctx,
+			  int aggr_idx)
+{
+	struct evsel * const *metric_events = mexp->metric_events;
+	struct metric_ref *metric_refs = mexp->metric_refs;
+	int i;
+
+	for (i = 0; metric_events[i]; i++) {
+		int source_count = 0, tool_aggr_idx;
+		int aggr_nr = 1;
+		bool is_tool_time =
+			tool_pmu__is_time_event(config, metric_events[i], &tool_aggr_idx);
+		struct perf_stat_evsel *ps = metric_events[i]->stats;
+		char *n;
+		double val;
+
+		/*
+		 * If there are multiple uncore PMUs and we're not reading the
+		 * leader's stats, determine the stats for the appropriate
+		 * uncore PMU.
+		 */
+		if (evsel && evsel->metric_leader &&
+		    evsel->pmu != evsel->metric_leader->pmu &&
+		    mexp->metric_events[i]->pmu == evsel->metric_leader->pmu) {
+			struct evsel *pos;
+
+			evlist__for_each_entry(evsel->evlist, pos) {
+				if (pos->pmu != evsel->pmu)
+					continue;
+				if (pos->metric_leader != mexp->metric_events[i])
+					continue;
+				ps = pos->stats;
+				source_count = 1;
+				break;
+			}
+		}
+		/* Time events are always on CPU0, the first aggregation index. */
+		if (!ps || !metric_events[i]->supported) {
+			/*
+			 * Not supported events will have a count of 0, which
+			 * can be confusing in a metric. Explicitly set the
+			 * value to NAN. Not counted events (enable time of 0)
+			 * are read as 0.
+			 */
+			val = NAN;
+			source_count = 0;
+			aggr_nr = 0;
+		} else {
+			struct perf_stat_aggr *aggr =
+				&ps->aggr[is_tool_time ? tool_aggr_idx : aggr_idx];
+
+			if (aggr->counts.run == 0) {
+				val = NAN;
+				source_count = 0;
+				aggr_nr = 0;
+			} else {
+				val = aggr->counts.val;
+				if (is_tool_time) {
+					/* Convert time event nanoseconds to seconds. */
+					val *= 1e-9;
+				}
+				if (!source_count)
+					source_count = evsel__source_count(metric_events[i]);
+				aggr_nr = aggr->nr ?: 1;
+			}
+		}
+		n = strdup(evsel__metric_id(metric_events[i]));
+		if (!n)
+			return -ENOMEM;
+
+		expr__add_id_val_source_count_aggr_nr(pctx, n, val, source_count, aggr_nr);
+	}
+
+	for (int j = 0; metric_refs && metric_refs[j].metric_name; j++) {
+		int ret = expr__add_ref(pctx, &metric_refs[j]);
+
+		if (ret)
+			return ret;
+	}
+
+	return i;
+}
+
+static void generic_metric(struct perf_stat_config *config,
+			   struct metric_expr *mexp,
+			   struct evsel *evsel,
+			   int aggr_idx,
+			   struct perf_stat_output_ctx *out)
+{
+	print_metric_t print_metric = out->print_metric;
+	const char *metric_name = mexp->metric_name;
+	const char *metric_expr = mexp->metric_expr;
+	const char *metric_threshold = mexp->metric_threshold;
+	const char *metric_unit = mexp->metric_unit;
+	struct evsel * const *metric_events = mexp->metric_events;
+	int runtime = mexp->runtime;
+	struct expr_parse_ctx *pctx;
+	double ratio, scale, threshold;
+	int i;
+	void *ctxp = out->ctx;
+	enum metric_threshold_classify thresh = METRIC_THRESHOLD_UNKNOWN;
+
+	pctx = expr__ctx_new();
+	if (!pctx)
+		return;
+
+	if (config->user_requested_cpu_list)
+		pctx->sctx.user_requested_cpu_list = strdup(config->user_requested_cpu_list);
+	pctx->sctx.runtime = runtime;
+	pctx->sctx.system_wide = config->system_wide;
+	i = prepare_metric(config, mexp, evsel, pctx, aggr_idx);
+	if (i < 0) {
+		expr__ctx_free(pctx);
+		return;
+	}
+	if (!metric_events[i]) {
+		if (expr__parse(&ratio, pctx, metric_expr) == 0) {
+			char *unit;
+			char metric_bf[128];
+
+			if (metric_threshold &&
+			    expr__parse(&threshold, pctx, metric_threshold) == 0 &&
+			    !isnan(threshold)) {
+				thresh = fpclassify(threshold) == FP_ZERO
+					? METRIC_THRESHOLD_GOOD : METRIC_THRESHOLD_BAD;
+			}
+
+			if (metric_unit && metric_name) {
+				if (perf_pmu__convert_scale(metric_unit,
+					&unit, &scale) >= 0) {
+					ratio *= scale;
+				}
+				if (strstr(metric_expr, "?"))
+					scnprintf(metric_bf, sizeof(metric_bf),
+					  "%s  %s_%d", unit, metric_name, runtime);
+				else
+					scnprintf(metric_bf, sizeof(metric_bf),
+					  "%s  %s", unit, metric_name);
+
+				print_metric(config, ctxp, thresh, "%8.1f",
+					     metric_bf, ratio);
+			} else {
+				print_metric(config, ctxp, thresh, "%8.2f",
+					metric_name ?
+					metric_name :
+					out->force_header ?  evsel->name : "",
+					ratio);
+			}
+		} else {
+			print_metric(config, ctxp, thresh, /*fmt=*/NULL,
+				     out->force_header ?
+				     (metric_name ?: evsel->name) : "", 0);
+		}
+	} else {
+		print_metric(config, ctxp, thresh, /*fmt=*/NULL,
+			     out->force_header ?
+			     (metric_name ?: evsel->name) : "", 0);
+	}
+
+	expr__ctx_free(pctx);
+}
+
+double test_generic_metric(struct metric_expr *mexp, int aggr_idx)
+{
+	struct expr_parse_ctx *pctx;
+	double ratio = 0.0;
+
+	pctx = expr__ctx_new();
+	if (!pctx)
+		return NAN;
+
+	if (prepare_metric(/*config=*/NULL, mexp, /*evsel=*/NULL, pctx, aggr_idx) < 0)
+		goto out;
+
+	if (expr__parse(&ratio, pctx, mexp->metric_expr))
+		ratio = 0.0;
+
+out:
+	expr__ctx_free(pctx);
+	return ratio;
+}
+
+static void perf_stat__print_metricgroup_header(struct perf_stat_config *config,
+						struct evsel *evsel,
+						void *ctxp,
+						const char *name,
+						struct perf_stat_output_ctx *out)
+{
+	bool need_full_name = perf_pmus__num_core_pmus() > 1;
+	static const char *last_name;
+	static const struct perf_pmu *last_pmu;
+	char full_name[64];
+
+	/*
+	 * A metricgroup may have several metric events,
+	 * e.g.,TopdownL1 on e-core of ADL.
+	 * The name has been output by the first metric
+	 * event. Only align with other metics from
+	 * different metric events.
+	 */
+	if (last_name && !strcmp(last_name, name) && last_pmu == evsel->pmu) {
+		out->print_metricgroup_header(config, ctxp, NULL);
+		return;
+	}
+
+	if (need_full_name && evsel->pmu)
+		scnprintf(full_name, sizeof(full_name), "%s (%s)", name, evsel->pmu->name);
+	else
+		scnprintf(full_name, sizeof(full_name), "%s", name);
+
+	out->print_metricgroup_header(config, ctxp, full_name);
+
+	last_name = name;
+	last_pmu = evsel->pmu;
+}
+
+/**
+ * perf_stat__print_shadow_stats_metricgroup - Print out metrics associated with the evsel
+ *					       For the non-default, all metrics associated
+ *					       with the evsel are printed.
+ *					       For the default mode, only the metrics from
+ *					       the same metricgroup and the name of the
+ *					       metricgroup are printed. To print the metrics
+ *					       from the next metricgroup (if available),
+ *					       invoke the function with correspoinding
+ *					       metric_expr.
+ */
+void *perf_stat__print_shadow_stats_metricgroup(struct perf_stat_config *config,
+						struct evsel *evsel,
+						int aggr_idx,
+						int *num,
+						void *from,
+						struct perf_stat_output_ctx *out)
+{
+	struct metric_event *me;
+	struct metric_expr *mexp = from;
+	void *ctxp = out->ctx;
+	bool header_printed = false;
+	const char *name = NULL;
+	struct rblist *metric_events = &evsel->evlist->metric_events;
+
+	me = metricgroup__lookup(metric_events, evsel, false);
+	if (me == NULL)
+		return NULL;
+
+	if (!mexp)
+		mexp = list_first_entry(&me->head, typeof(*mexp), nd);
+
+	list_for_each_entry_from(mexp, &me->head, nd) {
+		/* Print the display name of the Default metricgroup */
+		if (!config->metric_only && me->is_default) {
+			if (!name)
+				name = mexp->default_metricgroup_name;
+			/*
+			 * Two or more metricgroup may share the same metric
+			 * event, e.g., TopdownL1 and TopdownL2 on SPR.
+			 * Return and print the prefix, e.g., noise, running
+			 * for the next metricgroup.
+			 */
+			if (strcmp(name, mexp->default_metricgroup_name))
+				return (void *)mexp;
+			/* Only print the name of the metricgroup once */
+			if (!header_printed && !evsel->default_show_events) {
+				header_printed = true;
+				perf_stat__print_metricgroup_header(config, evsel, ctxp,
+								    name, out);
+			}
+		}
+
+		if ((*num)++ > 0 && out->new_line)
+			out->new_line(config, ctxp);
+		generic_metric(config, mexp, evsel, aggr_idx, out);
+	}
+
+	return NULL;
+}
+
+void perf_stat__print_shadow_stats(struct perf_stat_config *config,
+				   struct evsel *evsel,
+				   int aggr_idx,
+				   struct perf_stat_output_ctx *out)
+{
+	print_metric_t print_metric = out->print_metric;
+	void *ctxp = out->ctx;
+	int num = 0;
+
+	if (config->iostat_run)
+		iostat_print_metric(config, evsel, out);
+
+	perf_stat__print_shadow_stats_metricgroup(config, evsel, aggr_idx,
+						  &num, NULL, out);
+
+	if (num == 0) {
+		print_metric(config, ctxp, METRIC_THRESHOLD_UNKNOWN,
+			     /*fmt=*/NULL, /*unit=*/NULL, 0);
+	}
+}
+
+/**
+ * perf_stat__skip_metric_event - Skip the evsel in the Default metricgroup,
+ *				  if it's not running or not the metric event.
+ */
+bool perf_stat__skip_metric_event(struct evsel *evsel)
+{
+	if (!evsel->default_metricgroup)
+		return false;
+
+	return !metricgroup__lookup(&evsel->evlist->metric_events, evsel, false);
+}