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, 305 insertions, 0 deletions

diff --git a/tools/perf/tests/parse-metric.c b/tools/perf/tests/parse-metric.c
new file mode 100644
index 000000000..7c7f489a5
--- /dev/null
+++ b/tools/perf/tests/parse-metric.c
@@ -0,0 +1,305 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/compiler.h>
+#include <errno.h>
+#include <string.h>
+#include <perf/cpumap.h>
+#include <perf/evlist.h>
+#include "metricgroup.h"
+#include "tests.h"
+#include "pmu-events/pmu-events.h"
+#include "evlist.h"
+#include "rblist.h"
+#include "debug.h"
+#include "expr.h"
+#include "stat.h"
+#include "pmus.h"
+
+struct value {
+	const char	*event;
+	u64		 val;
+};
+
+static u64 find_value(const char *name, struct value *values)
+{
+	struct value *v = values;
+
+	while (v->event) {
+		if (!strcmp(name, v->event))
+			return v->val;
+		v++;
+	}
+	return 0;
+}
+
+static void load_runtime_stat(struct evlist *evlist, struct value *vals)
+{
+	struct evsel *evsel;
+	u64 count;
+
+	evlist__alloc_aggr_stats(evlist, 1);
+	evlist__for_each_entry(evlist, evsel) {
+		count = find_value(evsel->name, vals);
+		evsel->supported = true;
+		evsel->stats->aggr->counts.val = count;
+		evsel->stats->aggr->counts.ena = 1;
+		evsel->stats->aggr->counts.run = 1;
+	}
+}
+
+static double compute_single(struct evlist *evlist, const char *name)
+{
+	struct metric_expr *mexp;
+	struct metric_event *me;
+	struct evsel *evsel;
+
+	evlist__for_each_entry(evlist, evsel) {
+		me = metricgroup__lookup(&evlist->metric_events, evsel, false);
+		if (me != NULL) {
+			list_for_each_entry (mexp, &me->head, nd) {
+				if (strcmp(mexp->metric_name, name))
+					continue;
+				return test_generic_metric(mexp, 0);
+			}
+		}
+	}
+	return 0.;
+}
+
+static int __compute_metric(const char *name, struct value *vals,
+			    const char *name1, double *ratio1,
+			    const char *name2, double *ratio2)
+{
+	const struct pmu_metrics_table *pme_test;
+	struct perf_cpu_map *cpus;
+	struct evlist *evlist;
+	int err;
+
+	/*
+	 * We need to prepare evlist for stat mode running on CPU 0
+	 * because that's where all the stats are going to be created.
+	 */
+	evlist = evlist__new();
+	if (!evlist)
+		return -ENOMEM;
+
+	cpus = perf_cpu_map__new("0");
+	if (!cpus) {
+		evlist__delete(evlist);
+		return -ENOMEM;
+	}
+
+	perf_evlist__set_maps(&evlist->core, cpus, NULL);
+
+	/* Parse the metric into metric_events list. */
+	pme_test = find_core_metrics_table("testarch", "testcpu");
+	err = metricgroup__parse_groups_test(evlist, pme_test, name);
+	if (err)
+		goto out;
+
+	err = evlist__alloc_stats(/*config=*/NULL, evlist, /*alloc_raw=*/false);
+	if (err)
+		goto out;
+
+	/* Load the runtime stats with given numbers for events. */
+	load_runtime_stat(evlist, vals);
+
+	/* And execute the metric */
+	if (name1 && ratio1)
+		*ratio1 = compute_single(evlist, name1);
+	if (name2 && ratio2)
+		*ratio2 = compute_single(evlist, name2);
+
+out:
+	/* ... cleanup. */
+	evlist__free_stats(evlist);
+	perf_cpu_map__put(cpus);
+	evlist__delete(evlist);
+	return err;
+}
+
+static int compute_metric(const char *name, struct value *vals, double *ratio)
+{
+	return __compute_metric(name, vals, name, ratio, NULL, NULL);
+}
+
+static int compute_metric_group(const char *name, struct value *vals,
+				const char *name1, double *ratio1,
+				const char *name2, double *ratio2)
+{
+	return __compute_metric(name, vals, name1, ratio1, name2, ratio2);
+}
+
+static int test_ipc(void)
+{
+	double ratio;
+	struct value vals[] = {
+		{ .event = "inst_retired.any",        .val = 300 },
+		{ .event = "cpu_clk_unhalted.thread", .val = 200 },
+		{ .event = NULL, },
+	};
+
+	TEST_ASSERT_VAL("failed to compute metric",
+			compute_metric("IPC", vals, &ratio) == 0);
+
+	TEST_ASSERT_VAL("IPC failed, wrong ratio",
+			ratio == 1.5);
+	return 0;
+}
+
+static int test_frontend(void)
+{
+	double ratio;
+	struct value vals[] = {
+		{ .event = "idq_uops_not_delivered.core",        .val = 300 },
+		{ .event = "cpu_clk_unhalted.thread",            .val = 200 },
+		{ .event = "cpu_clk_unhalted.one_thread_active", .val = 400 },
+		{ .event = "cpu_clk_unhalted.ref_xclk",          .val = 600 },
+		{ .event = NULL, },
+	};
+
+	TEST_ASSERT_VAL("failed to compute metric",
+			compute_metric("Frontend_Bound_SMT", vals, &ratio) == 0);
+
+	TEST_ASSERT_VAL("Frontend_Bound_SMT failed, wrong ratio",
+			ratio == 0.45);
+	return 0;
+}
+
+static int test_cache_miss_cycles(void)
+{
+	double ratio;
+	struct value vals[] = {
+		{ .event = "l1d-loads-misses",  .val = 300 },
+		{ .event = "l1i-loads-misses",  .val = 200 },
+		{ .event = "inst_retired.any",  .val = 400 },
+		{ .event = NULL, },
+	};
+
+	TEST_ASSERT_VAL("failed to compute metric",
+			compute_metric("cache_miss_cycles", vals, &ratio) == 0);
+
+	TEST_ASSERT_VAL("cache_miss_cycles failed, wrong ratio",
+			ratio == 1.25);
+	return 0;
+}
+
+
+/*
+ * DCache_L2_All_Hits = l2_rqsts.demand_data_rd_hit + l2_rqsts.pf_hit + l2_rqsts.rfo_hi
+ * DCache_L2_All_Miss = max(l2_rqsts.all_demand_data_rd - l2_rqsts.demand_data_rd_hit, 0) +
+ *                      l2_rqsts.pf_miss + l2_rqsts.rfo_miss
+ * DCache_L2_All      = dcache_l2_all_hits + dcache_l2_all_miss
+ * DCache_L2_Hits     = d_ratio(dcache_l2_all_hits, dcache_l2_all)
+ * DCache_L2_Misses   = d_ratio(dcache_l2_all_miss, dcache_l2_all)
+ *
+ * l2_rqsts.demand_data_rd_hit = 100
+ * l2_rqsts.pf_hit             = 200
+ * l2_rqsts.rfo_hi             = 300
+ * l2_rqsts.all_demand_data_rd = 400
+ * l2_rqsts.pf_miss            = 500
+ * l2_rqsts.rfo_miss           = 600
+ *
+ * DCache_L2_All_Hits = 600
+ * DCache_L2_All_Miss = MAX(400 - 100, 0) + 500 + 600 = 1400
+ * DCache_L2_All      = 600 + 1400  = 2000
+ * DCache_L2_Hits     = 600 / 2000  = 0.3
+ * DCache_L2_Misses   = 1400 / 2000 = 0.7
+ */
+static int test_dcache_l2(void)
+{
+	double ratio;
+	struct value vals[] = {
+		{ .event = "l2_rqsts.demand_data_rd_hit", .val = 100 },
+		{ .event = "l2_rqsts.pf_hit",             .val = 200 },
+		{ .event = "l2_rqsts.rfo_hit",            .val = 300 },
+		{ .event = "l2_rqsts.all_demand_data_rd", .val = 400 },
+		{ .event = "l2_rqsts.pf_miss",            .val = 500 },
+		{ .event = "l2_rqsts.rfo_miss",           .val = 600 },
+		{ .event = NULL, },
+	};
+
+	TEST_ASSERT_VAL("failed to compute metric",
+			compute_metric("DCache_L2_Hits", vals, &ratio) == 0);
+
+	TEST_ASSERT_VAL("DCache_L2_Hits failed, wrong ratio",
+			ratio == 0.3);
+
+	TEST_ASSERT_VAL("failed to compute metric",
+			compute_metric("DCache_L2_Misses", vals, &ratio) == 0);
+
+	TEST_ASSERT_VAL("DCache_L2_Misses failed, wrong ratio",
+			ratio == 0.7);
+	return 0;
+}
+
+static int test_recursion_fail(void)
+{
+	double ratio;
+	struct value vals[] = {
+		{ .event = "inst_retired.any",        .val = 300 },
+		{ .event = "cpu_clk_unhalted.thread", .val = 200 },
+		{ .event = NULL, },
+	};
+
+	TEST_ASSERT_VAL("failed to find recursion",
+			compute_metric("M1", vals, &ratio) == -1);
+
+	TEST_ASSERT_VAL("failed to find recursion",
+			compute_metric("M3", vals, &ratio) == -1);
+	return 0;
+}
+
+static int test_memory_bandwidth(void)
+{
+	double ratio;
+	struct value vals[] = {
+		{ .event = "l1d.replacement", .val = 4000000 },
+		{ .event = "duration_time",  .val = 200000000 },
+		{ .event = NULL, },
+	};
+
+	TEST_ASSERT_VAL("failed to compute metric",
+			compute_metric("L1D_Cache_Fill_BW", vals, &ratio) == 0);
+	TEST_ASSERT_VAL("L1D_Cache_Fill_BW, wrong ratio",
+			1.28 == ratio);
+
+	return 0;
+}
+
+static int test_metric_group(void)
+{
+	double ratio1, ratio2;
+	struct value vals[] = {
+		{ .event = "cpu_clk_unhalted.thread", .val = 200 },
+		{ .event = "l1d-loads-misses",        .val = 300 },
+		{ .event = "l1i-loads-misses",        .val = 200 },
+		{ .event = "inst_retired.any",        .val = 400 },
+		{ .event = NULL, },
+	};
+
+	TEST_ASSERT_VAL("failed to find recursion",
+			compute_metric_group("group1", vals,
+					     "IPC", &ratio1,
+					     "cache_miss_cycles", &ratio2) == 0);
+
+	TEST_ASSERT_VAL("group IPC failed, wrong ratio",
+			ratio1 == 2.0);
+
+	TEST_ASSERT_VAL("group cache_miss_cycles failed, wrong ratio",
+			ratio2 == 1.25);
+	return 0;
+}
+
+static int test__parse_metric(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	TEST_ASSERT_VAL("IPC failed", test_ipc() == 0);
+	TEST_ASSERT_VAL("frontend failed", test_frontend() == 0);
+	TEST_ASSERT_VAL("DCache_L2 failed", test_dcache_l2() == 0);
+	TEST_ASSERT_VAL("recursion fail failed", test_recursion_fail() == 0);
+	TEST_ASSERT_VAL("Memory bandwidth", test_memory_bandwidth() == 0);
+	TEST_ASSERT_VAL("cache_miss_cycles failed", test_cache_miss_cycles() == 0);
+	TEST_ASSERT_VAL("test metric group", test_metric_group() == 0);
+	return 0;
+}
+
+DEFINE_SUITE("Parse and process metrics", parse_metric);