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, 318 insertions, 0 deletions

diff --git a/lib/tests/hashtable_test.c b/lib/tests/hashtable_test.c
new file mode 100644
index 000000000..3521de6ba
--- /dev/null
+++ b/lib/tests/hashtable_test.c
@@ -0,0 +1,318 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for the Kernel Hashtable structures.
+ *
+ * Copyright (C) 2022, Google LLC.
+ * Author: Rae Moar <rmoar@google.com>
+ */
+#include <kunit/test.h>
+
+#include <linux/hashtable.h>
+
+struct hashtable_test_entry {
+	int key;
+	int data;
+	struct hlist_node node;
+	int visited;
+};
+
+static void hashtable_test_hash_init(struct kunit *test)
+{
+	/* Test the different ways of initialising a hashtable. */
+	DEFINE_HASHTABLE(hash1, 2);
+	DECLARE_HASHTABLE(hash2, 3);
+
+	/* When using DECLARE_HASHTABLE, must use hash_init to
+	 * initialize the hashtable.
+	 */
+	hash_init(hash2);
+
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash1));
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash2));
+}
+
+static void hashtable_test_hash_empty(struct kunit *test)
+{
+	struct hashtable_test_entry a;
+	DEFINE_HASHTABLE(hash, 1);
+
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash));
+
+	a.key = 1;
+	a.data = 13;
+	hash_add(hash, &a.node, a.key);
+
+	/* Hashtable should no longer be empty. */
+	KUNIT_EXPECT_FALSE(test, hash_empty(hash));
+}
+
+static void hashtable_test_hash_hashed(struct kunit *test)
+{
+	struct hashtable_test_entry a, b;
+	DEFINE_HASHTABLE(hash, 4);
+
+	a.key = 1;
+	a.data = 13;
+	hash_add(hash, &a.node, a.key);
+	b.key = 1;
+	b.data = 2;
+	hash_add(hash, &b.node, b.key);
+
+	KUNIT_EXPECT_TRUE(test, hash_hashed(&a.node));
+	KUNIT_EXPECT_TRUE(test, hash_hashed(&b.node));
+}
+
+static void hashtable_test_hash_add(struct kunit *test)
+{
+	struct hashtable_test_entry a, b, *x;
+	int bkt;
+	DEFINE_HASHTABLE(hash, 3);
+
+	a.key = 1;
+	a.data = 13;
+	a.visited = 0;
+	hash_add(hash, &a.node, a.key);
+	b.key = 2;
+	b.data = 10;
+	b.visited = 0;
+	hash_add(hash, &b.node, b.key);
+
+	hash_for_each(hash, bkt, x, node) {
+		x->visited++;
+		if (x->key == a.key)
+			KUNIT_EXPECT_EQ(test, x->data, 13);
+		else if (x->key == b.key)
+			KUNIT_EXPECT_EQ(test, x->data, 10);
+		else
+			KUNIT_FAIL(test, "Unexpected key in hashtable.");
+	}
+
+	/* Both entries should have been visited exactly once. */
+	KUNIT_EXPECT_EQ(test, a.visited, 1);
+	KUNIT_EXPECT_EQ(test, b.visited, 1);
+}
+
+static void hashtable_test_hash_del(struct kunit *test)
+{
+	struct hashtable_test_entry a, b, *x;
+	DEFINE_HASHTABLE(hash, 6);
+
+	a.key = 1;
+	a.data = 13;
+	hash_add(hash, &a.node, a.key);
+	b.key = 2;
+	b.data = 10;
+	b.visited = 0;
+	hash_add(hash, &b.node, b.key);
+
+	hash_del(&b.node);
+	hash_for_each_possible(hash, x, node, b.key) {
+		x->visited++;
+		KUNIT_EXPECT_NE(test, x->key, b.key);
+	}
+
+	/* The deleted entry should not have been visited. */
+	KUNIT_EXPECT_EQ(test, b.visited, 0);
+
+	hash_del(&a.node);
+
+	/* The hashtable should be empty. */
+	KUNIT_EXPECT_TRUE(test, hash_empty(hash));
+}
+
+static void hashtable_test_hash_for_each(struct kunit *test)
+{
+	struct hashtable_test_entry entries[3];
+	struct hashtable_test_entry *x;
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 3);
+
+	/* Add three entries to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = i;
+		entries[i].data = i + 10;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	count = 0;
+	hash_for_each(hash, bkt, x, node) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->key, 3, "Unexpected key in hashtable.");
+		count++;
+	}
+
+	/* Should have visited each entry exactly once. */
+	KUNIT_EXPECT_EQ(test, count, 3);
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+}
+
+static void hashtable_test_hash_for_each_safe(struct kunit *test)
+{
+	struct hashtable_test_entry entries[3];
+	struct hashtable_test_entry *x;
+	struct hlist_node *tmp;
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 3);
+
+	/* Add three entries to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = i;
+		entries[i].data = i + 10;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	count = 0;
+	hash_for_each_safe(hash, bkt, tmp, x, node) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->key, 3, "Unexpected key in hashtable.");
+		count++;
+
+		/* Delete entry during loop. */
+		hash_del(&x->node);
+	}
+
+	/* Should have visited each entry exactly once. */
+	KUNIT_EXPECT_EQ(test, count, 3);
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+}
+
+static void hashtable_test_hash_for_each_possible(struct kunit *test)
+{
+	struct hashtable_test_entry entries[4];
+	struct hashtable_test_entry *x, *y;
+	int buckets[2];
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 5);
+
+	/* Add three entries with key = 0 to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = 0;
+		entries[i].data = i;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	/* Add an entry with key = 1. */
+	entries[3].key = 1;
+	entries[3].data = 3;
+	entries[3].visited = 0;
+	hash_add(hash, &entries[3].node, entries[3].key);
+
+	count = 0;
+	hash_for_each_possible(hash, x, node, 0) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->data, 0, "Unexpected data in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->data, 4, "Unexpected data in hashtable.");
+		count++;
+	}
+
+	/* Should have visited each entry with key = 0 exactly once. */
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+
+	/* Save the buckets for the different keys. */
+	hash_for_each(hash, bkt, y, node) {
+		KUNIT_ASSERT_GE_MSG(test, y->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LE_MSG(test, y->key, 1, "Unexpected key in hashtable.");
+		buckets[y->key] = bkt;
+	}
+
+	/* If entry with key = 1 is in the same bucket as the entries with
+	 * key = 0, check it was visited. Otherwise ensure that only three
+	 * entries were visited.
+	 */
+	if (buckets[0] == buckets[1]) {
+		KUNIT_EXPECT_EQ(test, count, 4);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 1);
+	} else {
+		KUNIT_EXPECT_EQ(test, count, 3);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 0);
+	}
+}
+
+static void hashtable_test_hash_for_each_possible_safe(struct kunit *test)
+{
+	struct hashtable_test_entry entries[4];
+	struct hashtable_test_entry *x, *y;
+	struct hlist_node *tmp;
+	int buckets[2];
+	int bkt, i, j, count;
+	DEFINE_HASHTABLE(hash, 5);
+
+	/* Add three entries with key = 0 to the hashtable. */
+	for (i = 0; i < 3; i++) {
+		entries[i].key = 0;
+		entries[i].data = i;
+		entries[i].visited = 0;
+		hash_add(hash, &entries[i].node, entries[i].key);
+	}
+
+	/* Add an entry with key = 1. */
+	entries[3].key = 1;
+	entries[3].data = 3;
+	entries[3].visited = 0;
+	hash_add(hash, &entries[3].node, entries[3].key);
+
+	count = 0;
+	hash_for_each_possible_safe(hash, x, tmp, node, 0) {
+		x->visited += 1;
+		KUNIT_ASSERT_GE_MSG(test, x->data, 0, "Unexpected data in hashtable.");
+		KUNIT_ASSERT_LT_MSG(test, x->data, 4, "Unexpected data in hashtable.");
+		count++;
+
+		/* Delete entry during loop. */
+		hash_del(&x->node);
+	}
+
+	/* Should have visited each entry with key = 0 exactly once. */
+	for (j = 0; j < 3; j++)
+		KUNIT_EXPECT_EQ(test, entries[j].visited, 1);
+
+	/* Save the buckets for the different keys. */
+	hash_for_each(hash, bkt, y, node) {
+		KUNIT_ASSERT_GE_MSG(test, y->key, 0, "Unexpected key in hashtable.");
+		KUNIT_ASSERT_LE_MSG(test, y->key, 1, "Unexpected key in hashtable.");
+		buckets[y->key] = bkt;
+	}
+
+	/* If entry with key = 1 is in the same bucket as the entries with
+	 * key = 0, check it was visited. Otherwise ensure that only three
+	 * entries were visited.
+	 */
+	if (buckets[0] == buckets[1]) {
+		KUNIT_EXPECT_EQ(test, count, 4);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 1);
+	} else {
+		KUNIT_EXPECT_EQ(test, count, 3);
+		KUNIT_EXPECT_EQ(test, entries[3].visited, 0);
+	}
+}
+
+static struct kunit_case hashtable_test_cases[] = {
+	KUNIT_CASE(hashtable_test_hash_init),
+	KUNIT_CASE(hashtable_test_hash_empty),
+	KUNIT_CASE(hashtable_test_hash_hashed),
+	KUNIT_CASE(hashtable_test_hash_add),
+	KUNIT_CASE(hashtable_test_hash_del),
+	KUNIT_CASE(hashtable_test_hash_for_each),
+	KUNIT_CASE(hashtable_test_hash_for_each_safe),
+	KUNIT_CASE(hashtable_test_hash_for_each_possible),
+	KUNIT_CASE(hashtable_test_hash_for_each_possible_safe),
+	{},
+};
+
+static struct kunit_suite hashtable_test_module = {
+	.name = "hashtable",
+	.test_cases = hashtable_test_cases,
+};
+
+kunit_test_suites(&hashtable_test_module);
+
+MODULE_DESCRIPTION("KUnit test for the Kernel Hashtable structures");
+MODULE_LICENSE("GPL");