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, 324 insertions, 0 deletions

diff --git a/drivers/interconnect/icc-kunit.c b/drivers/interconnect/icc-kunit.c
new file mode 100644
index 000000000..bad2b5837
--- /dev/null
+++ b/drivers/interconnect/icc-kunit.c
@@ -0,0 +1,324 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for the Interconnect framework.
+ *
+ * Copyright (c) 2025 Kuan-Wei Chiu <visitorckw@gmail.com>
+ *
+ * This suite verifies the behavior of the interconnect core, including
+ * topology construction, bandwidth aggregation, and path lifecycle.
+ */
+
+#include <kunit/platform_device.h>
+#include <kunit/test.h>
+#include <linux/interconnect-provider.h>
+#include <linux/interconnect.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/overflow.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+#include "internal.h"
+
+enum {
+	NODE_CPU,
+	NODE_GPU,
+	NODE_BUS,
+	NODE_DDR,
+	NODE_MAX
+};
+
+struct test_node_data {
+	int id;
+	const char *name;
+	int num_links;
+	int links[2];
+};
+
+/*
+ * Static Topology:
+ * CPU -\
+ * -> BUS -> DDR
+ * GPU -/
+ */
+static const struct test_node_data test_topology[] = {
+	{ NODE_CPU, "cpu", 1, { NODE_BUS } },
+	{ NODE_GPU, "gpu", 1, { NODE_BUS } },
+	{ NODE_BUS, "bus", 1, { NODE_DDR } },
+	{ NODE_DDR, "ddr", 0, { } },
+};
+
+struct icc_test_priv {
+	struct icc_provider provider;
+	struct platform_device *pdev;
+	struct icc_node *nodes[NODE_MAX];
+};
+
+static struct icc_node *get_node(struct icc_test_priv *priv, int id)
+{
+	int idx = id - NODE_CPU;
+
+	if (idx < 0 || idx >= ARRAY_SIZE(test_topology))
+		return NULL;
+	return priv->nodes[idx];
+}
+
+static int icc_test_set(struct icc_node *src, struct icc_node *dst)
+{
+	return 0;
+}
+
+static int icc_test_aggregate(struct icc_node *node, u32 tag, u32 avg_bw,
+			      u32 peak_bw, u32 *agg_avg, u32 *agg_peak)
+{
+	return icc_std_aggregate(node, tag, avg_bw, peak_bw, agg_avg, agg_peak);
+}
+
+static struct icc_node *icc_test_xlate(const struct of_phandle_args *spec, void *data)
+{
+	return NULL;
+}
+
+static int icc_test_get_bw(struct icc_node *node, u32 *avg, u32 *peak)
+{
+	*avg = 0;
+	*peak = 0;
+
+	return 0;
+}
+
+static int icc_test_init(struct kunit *test)
+{
+	struct icc_test_priv *priv;
+	struct icc_node *node;
+	int i, j, ret;
+
+	priv = kunit_kzalloc(test, sizeof(*priv), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv);
+	test->priv = priv;
+
+	priv->pdev = kunit_platform_device_alloc(test, "icc-test-dev", -1);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv->pdev);
+	KUNIT_ASSERT_EQ(test, kunit_platform_device_add(test, priv->pdev), 0);
+
+	priv->provider.set = icc_test_set;
+	priv->provider.aggregate = icc_test_aggregate;
+	priv->provider.xlate = icc_test_xlate;
+	priv->provider.get_bw = icc_test_get_bw;
+	priv->provider.dev = &priv->pdev->dev;
+	priv->provider.data = priv;
+	INIT_LIST_HEAD(&priv->provider.nodes);
+
+	ret = icc_provider_register(&priv->provider);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	for (i = 0; i < ARRAY_SIZE(test_topology); i++) {
+		const struct test_node_data *data = &test_topology[i];
+
+		node = icc_node_create(data->id);
+		KUNIT_ASSERT_NOT_ERR_OR_NULL(test, node);
+
+		node->name = data->name;
+		icc_node_add(node, &priv->provider);
+		priv->nodes[i] = node;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(test_topology); i++) {
+		const struct test_node_data *data = &test_topology[i];
+		struct icc_node *src = get_node(priv, data->id);
+
+		for (j = 0; j < data->num_links; j++) {
+			ret = icc_link_create(src, data->links[j]);
+			KUNIT_ASSERT_EQ_MSG(test, ret, 0, "Failed to link %s->%d",
+					    src->name, data->links[j]);
+		}
+	}
+
+	icc_sync_state(&priv->pdev->dev);
+
+	return 0;
+}
+
+static void icc_test_exit(struct kunit *test)
+{
+	struct icc_test_priv *priv = test->priv;
+
+	icc_nodes_remove(&priv->provider);
+	icc_provider_deregister(&priv->provider);
+}
+
+/*
+ * Helper to construct a mock path.
+ *
+ * Because we are bypassing icc_get(), we must manually link the requests
+ * to the nodes' req_list so that icc_std_aggregate() can discover them.
+ */
+static struct icc_path *icc_test_create_path(struct kunit *test,
+					     struct icc_node **nodes, int num)
+{
+	struct icc_path *path;
+	int i;
+
+	path = kunit_kzalloc(test, struct_size(path, reqs, num), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, path);
+
+	path->num_nodes = num;
+	for (i = 0; i < num; i++) {
+		path->reqs[i].node = nodes[i];
+		hlist_add_head(&path->reqs[i].req_node, &nodes[i]->req_list);
+	}
+	path->name = "mock-path";
+
+	return path;
+}
+
+static void icc_test_destroy_path(struct kunit *test, struct icc_path *path)
+{
+	int i;
+
+	for (i = 0; i < path->num_nodes; i++)
+		hlist_del(&path->reqs[i].req_node);
+
+	kunit_kfree(test, path);
+}
+
+static void icc_test_topology_integrity(struct kunit *test)
+{
+	struct icc_test_priv *priv = test->priv;
+	struct icc_node *cpu = get_node(priv, NODE_CPU);
+	struct icc_node *bus = get_node(priv, NODE_BUS);
+
+	KUNIT_EXPECT_EQ(test, cpu->num_links, 1);
+	KUNIT_EXPECT_PTR_EQ(test, cpu->links[0], bus);
+	KUNIT_EXPECT_PTR_EQ(test, cpu->provider, &priv->provider);
+}
+
+static void icc_test_set_bw(struct kunit *test)
+{
+	struct icc_test_priv *priv = test->priv;
+	struct icc_path *path;
+	struct icc_node *path_nodes[3];
+	int ret;
+
+	/* Path: CPU -> BUS -> DDR */
+	path_nodes[0] = get_node(priv, NODE_CPU);
+	path_nodes[1] = get_node(priv, NODE_BUS);
+	path_nodes[2] = get_node(priv, NODE_DDR);
+
+	path = icc_test_create_path(test, path_nodes, 3);
+
+	ret = icc_enable(path);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+
+	ret = icc_set_bw(path, 1000, 2000);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+
+	KUNIT_EXPECT_EQ(test, path_nodes[0]->avg_bw, 1000);
+	KUNIT_EXPECT_EQ(test, path_nodes[0]->peak_bw, 2000);
+	KUNIT_EXPECT_EQ(test, path_nodes[1]->avg_bw, 1000);
+	KUNIT_EXPECT_EQ(test, path_nodes[1]->peak_bw, 2000);
+
+	icc_set_tag(path, 0xABC);
+	KUNIT_EXPECT_EQ(test, path->reqs[0].tag, 0xABC);
+
+	icc_disable(path);
+	KUNIT_EXPECT_EQ(test, path_nodes[0]->avg_bw, 0);
+
+	icc_test_destroy_path(test, path);
+}
+
+static void icc_test_aggregation(struct kunit *test)
+{
+	struct icc_test_priv *priv = test->priv;
+	struct icc_path *path_cpu, *path_gpu;
+	struct icc_node *nodes_cpu[3], *nodes_gpu[2];
+	struct icc_node *bus = get_node(priv, NODE_BUS);
+	int ret;
+
+	nodes_cpu[0] = get_node(priv, NODE_CPU);
+	nodes_cpu[1] = bus;
+	nodes_cpu[2] = get_node(priv, NODE_DDR);
+	path_cpu = icc_test_create_path(test, nodes_cpu, 3);
+
+	nodes_gpu[0] = get_node(priv, NODE_GPU);
+	nodes_gpu[1] = bus;
+	path_gpu = icc_test_create_path(test, nodes_gpu, 2);
+
+	icc_enable(path_cpu);
+	icc_enable(path_gpu);
+
+	ret = icc_set_bw(path_cpu, 1000, 1000);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	KUNIT_EXPECT_EQ(test, bus->avg_bw, 1000);
+
+	ret = icc_set_bw(path_gpu, 2000, 2000);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+
+	/* Bus aggregates: CPU(1000) + GPU(2000) */
+	KUNIT_EXPECT_EQ(test, bus->avg_bw, 3000);
+	/* Peak aggregates: max(CPU, GPU) */
+	KUNIT_EXPECT_EQ(test, bus->peak_bw, 2000);
+
+	icc_test_destroy_path(test, path_cpu);
+	icc_test_destroy_path(test, path_gpu);
+}
+
+static void icc_test_bulk_ops(struct kunit *test)
+{
+	struct icc_test_priv *priv = test->priv;
+	struct icc_node *nodes_cpu[3], *nodes_gpu[2];
+	struct icc_bulk_data bulk[2];
+	int ret;
+
+	nodes_cpu[0] = get_node(priv, NODE_CPU);
+	nodes_cpu[1] = get_node(priv, NODE_BUS);
+	nodes_cpu[2] = get_node(priv, NODE_DDR);
+
+	nodes_gpu[0] = get_node(priv, NODE_GPU);
+	nodes_gpu[1] = get_node(priv, NODE_BUS);
+
+	bulk[0].path = icc_test_create_path(test, nodes_cpu, 3);
+	bulk[0].avg_bw = 500;
+	bulk[0].peak_bw = 500;
+
+	bulk[1].path = icc_test_create_path(test, nodes_gpu, 2);
+	bulk[1].avg_bw = 600;
+	bulk[1].peak_bw = 600;
+
+	ret = icc_bulk_set_bw(2, bulk);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	/* Paths disabled, bandwidth should be 0 */
+	KUNIT_EXPECT_EQ(test, get_node(priv, NODE_BUS)->avg_bw, 0);
+
+	ret = icc_bulk_enable(2, bulk);
+	KUNIT_EXPECT_EQ(test, ret, 0);
+	/* Paths enabled, aggregation applies */
+	KUNIT_EXPECT_EQ(test, get_node(priv, NODE_BUS)->avg_bw, 1100);
+
+	icc_bulk_disable(2, bulk);
+	KUNIT_EXPECT_EQ(test, get_node(priv, NODE_BUS)->avg_bw, 0);
+
+	icc_test_destroy_path(test, bulk[0].path);
+	icc_test_destroy_path(test, bulk[1].path);
+}
+
+static struct kunit_case icc_test_cases[] = {
+	KUNIT_CASE(icc_test_topology_integrity),
+	KUNIT_CASE(icc_test_set_bw),
+	KUNIT_CASE(icc_test_aggregation),
+	KUNIT_CASE(icc_test_bulk_ops),
+	{}
+};
+
+static struct kunit_suite icc_test_suite = {
+	.name = "interconnect",
+	.init = icc_test_init,
+	.exit = icc_test_exit,
+	.test_cases = icc_test_cases,
+};
+
+kunit_test_suite(icc_test_suite);
+
+MODULE_AUTHOR("Kuan-Wei Chiu <visitorckw@gmail.com>");
+MODULE_DESCRIPTION("KUnit tests for the Interconnect framework");
+MODULE_LICENSE("GPL");