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, 426 insertions, 0 deletions

diff --git a/lib/rbtree_test.c b/lib/rbtree_test.c
new file mode 100644
index 000000000..768c5e645
--- /dev/null
+++ b/lib/rbtree_test.c
@@ -0,0 +1,426 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/rbtree_augmented.h>
+#include <linux/prandom.h>
+#include <linux/slab.h>
+#include <asm/timex.h>
+
+#define __param(type, name, init, msg)		\
+	static type name = init;		\
+	module_param(name, type, 0444);		\
+	MODULE_PARM_DESC(name, msg);
+
+__param(int, nnodes, 100, "Number of nodes in the rb-tree");
+__param(int, perf_loops, 1000, "Number of iterations modifying the rb-tree");
+__param(int, check_loops, 100, "Number of iterations modifying and verifying the rb-tree");
+__param(ullong, seed, 3141592653589793238ULL, "Random seed");
+
+struct test_node {
+	u32 key;
+	struct rb_node rb;
+
+	/* following fields used for testing augmented rbtree functionality */
+	u32 val;
+	u32 augmented;
+};
+
+static struct rb_root_cached root = RB_ROOT_CACHED;
+static struct test_node *nodes = NULL;
+
+static struct rnd_state rnd;
+
+static void insert(struct test_node *node, struct rb_root_cached *root)
+{
+	struct rb_node **new = &root->rb_root.rb_node, *parent = NULL;
+	u32 key = node->key;
+
+	while (*new) {
+		parent = *new;
+		if (key < rb_entry(parent, struct test_node, rb)->key)
+			new = &parent->rb_left;
+		else
+			new = &parent->rb_right;
+	}
+
+	rb_link_node(&node->rb, parent, new);
+	rb_insert_color(&node->rb, &root->rb_root);
+}
+
+static void insert_cached(struct test_node *node, struct rb_root_cached *root)
+{
+	struct rb_node **new = &root->rb_root.rb_node, *parent = NULL;
+	u32 key = node->key;
+	bool leftmost = true;
+
+	while (*new) {
+		parent = *new;
+		if (key < rb_entry(parent, struct test_node, rb)->key)
+			new = &parent->rb_left;
+		else {
+			new = &parent->rb_right;
+			leftmost = false;
+		}
+	}
+
+	rb_link_node(&node->rb, parent, new);
+	rb_insert_color_cached(&node->rb, root, leftmost);
+}
+
+static inline void erase(struct test_node *node, struct rb_root_cached *root)
+{
+	rb_erase(&node->rb, &root->rb_root);
+}
+
+static inline void erase_cached(struct test_node *node, struct rb_root_cached *root)
+{
+	rb_erase_cached(&node->rb, root);
+}
+
+
+#define NODE_VAL(node) ((node)->val)
+
+RB_DECLARE_CALLBACKS_MAX(static, augment_callbacks,
+			 struct test_node, rb, u32, augmented, NODE_VAL)
+
+static void insert_augmented(struct test_node *node,
+			     struct rb_root_cached *root)
+{
+	struct rb_node **new = &root->rb_root.rb_node, *rb_parent = NULL;
+	u32 key = node->key;
+	u32 val = node->val;
+	struct test_node *parent;
+
+	while (*new) {
+		rb_parent = *new;
+		parent = rb_entry(rb_parent, struct test_node, rb);
+		if (parent->augmented < val)
+			parent->augmented = val;
+		if (key < parent->key)
+			new = &parent->rb.rb_left;
+		else
+			new = &parent->rb.rb_right;
+	}
+
+	node->augmented = val;
+	rb_link_node(&node->rb, rb_parent, new);
+	rb_insert_augmented(&node->rb, &root->rb_root, &augment_callbacks);
+}
+
+static void insert_augmented_cached(struct test_node *node,
+				    struct rb_root_cached *root)
+{
+	struct rb_node **new = &root->rb_root.rb_node, *rb_parent = NULL;
+	u32 key = node->key;
+	u32 val = node->val;
+	struct test_node *parent;
+	bool leftmost = true;
+
+	while (*new) {
+		rb_parent = *new;
+		parent = rb_entry(rb_parent, struct test_node, rb);
+		if (parent->augmented < val)
+			parent->augmented = val;
+		if (key < parent->key)
+			new = &parent->rb.rb_left;
+		else {
+			new = &parent->rb.rb_right;
+			leftmost = false;
+		}
+	}
+
+	node->augmented = val;
+	rb_link_node(&node->rb, rb_parent, new);
+	rb_insert_augmented_cached(&node->rb, root,
+				   leftmost, &augment_callbacks);
+}
+
+
+static void erase_augmented(struct test_node *node, struct rb_root_cached *root)
+{
+	rb_erase_augmented(&node->rb, &root->rb_root, &augment_callbacks);
+}
+
+static void erase_augmented_cached(struct test_node *node,
+				   struct rb_root_cached *root)
+{
+	rb_erase_augmented_cached(&node->rb, root, &augment_callbacks);
+}
+
+static void init(void)
+{
+	int i;
+	for (i = 0; i < nnodes; i++) {
+		nodes[i].key = prandom_u32_state(&rnd);
+		nodes[i].val = prandom_u32_state(&rnd);
+	}
+}
+
+static bool is_red(struct rb_node *rb)
+{
+	return !(rb->__rb_parent_color & 1);
+}
+
+static int black_path_count(struct rb_node *rb)
+{
+	int count;
+	for (count = 0; rb; rb = rb_parent(rb))
+		count += !is_red(rb);
+	return count;
+}
+
+static void check_postorder_foreach(int nr_nodes)
+{
+	struct test_node *cur, *n;
+	int count = 0;
+	rbtree_postorder_for_each_entry_safe(cur, n, &root.rb_root, rb)
+		count++;
+
+	WARN_ON_ONCE(count != nr_nodes);
+}
+
+static void check_postorder(int nr_nodes)
+{
+	struct rb_node *rb;
+	int count = 0;
+	for (rb = rb_first_postorder(&root.rb_root); rb; rb = rb_next_postorder(rb))
+		count++;
+
+	WARN_ON_ONCE(count != nr_nodes);
+}
+
+static void check(int nr_nodes)
+{
+	struct rb_node *rb;
+	int count = 0, blacks = 0;
+	u32 prev_key = 0;
+
+	for (rb = rb_first(&root.rb_root); rb; rb = rb_next(rb)) {
+		struct test_node *node = rb_entry(rb, struct test_node, rb);
+		WARN_ON_ONCE(node->key < prev_key);
+		WARN_ON_ONCE(is_red(rb) &&
+			     (!rb_parent(rb) || is_red(rb_parent(rb))));
+		if (!count)
+			blacks = black_path_count(rb);
+		else
+			WARN_ON_ONCE((!rb->rb_left || !rb->rb_right) &&
+				     blacks != black_path_count(rb));
+		prev_key = node->key;
+		count++;
+	}
+
+	WARN_ON_ONCE(count != nr_nodes);
+	WARN_ON_ONCE(count < (1 << black_path_count(rb_last(&root.rb_root))) - 1);
+
+	check_postorder(nr_nodes);
+	check_postorder_foreach(nr_nodes);
+}
+
+static void check_augmented(int nr_nodes)
+{
+	struct rb_node *rb;
+
+	check(nr_nodes);
+	for (rb = rb_first(&root.rb_root); rb; rb = rb_next(rb)) {
+		struct test_node *node = rb_entry(rb, struct test_node, rb);
+		u32 subtree, max = node->val;
+		if (node->rb.rb_left) {
+			subtree = rb_entry(node->rb.rb_left, struct test_node,
+					   rb)->augmented;
+			if (max < subtree)
+				max = subtree;
+		}
+		if (node->rb.rb_right) {
+			subtree = rb_entry(node->rb.rb_right, struct test_node,
+					   rb)->augmented;
+			if (max < subtree)
+				max = subtree;
+		}
+		WARN_ON_ONCE(node->augmented != max);
+	}
+}
+
+static int basic_check(void)
+{
+	int i, j;
+	cycles_t time1, time2, time;
+	struct rb_node *node;
+
+	printk(KERN_ALERT "rbtree testing");
+
+	init();
+
+	time1 = get_cycles();
+
+	for (i = 0; i < perf_loops; i++) {
+		for (j = 0; j < nnodes; j++)
+			insert(nodes + j, &root);
+		for (j = 0; j < nnodes; j++)
+			erase(nodes + j, &root);
+	}
+
+	time2 = get_cycles();
+	time = time2 - time1;
+
+	time = div_u64(time, perf_loops);
+	printk(" -> test 1 (latency of nnodes insert+delete): %llu cycles\n",
+	       (unsigned long long)time);
+
+	time1 = get_cycles();
+
+	for (i = 0; i < perf_loops; i++) {
+		for (j = 0; j < nnodes; j++)
+			insert_cached(nodes + j, &root);
+		for (j = 0; j < nnodes; j++)
+			erase_cached(nodes + j, &root);
+	}
+
+	time2 = get_cycles();
+	time = time2 - time1;
+
+	time = div_u64(time, perf_loops);
+	printk(" -> test 2 (latency of nnodes cached insert+delete): %llu cycles\n",
+	       (unsigned long long)time);
+
+	for (i = 0; i < nnodes; i++)
+		insert(nodes + i, &root);
+
+	time1 = get_cycles();
+
+	for (i = 0; i < perf_loops; i++) {
+		for (node = rb_first(&root.rb_root); node; node = rb_next(node))
+			;
+	}
+
+	time2 = get_cycles();
+	time = time2 - time1;
+
+	time = div_u64(time, perf_loops);
+	printk(" -> test 3 (latency of inorder traversal): %llu cycles\n",
+	       (unsigned long long)time);
+
+	time1 = get_cycles();
+
+	for (i = 0; i < perf_loops; i++)
+		node = rb_first(&root.rb_root);
+
+	time2 = get_cycles();
+	time = time2 - time1;
+
+	time = div_u64(time, perf_loops);
+	printk(" -> test 4 (latency to fetch first node)\n");
+	printk("        non-cached: %llu cycles\n", (unsigned long long)time);
+
+	time1 = get_cycles();
+
+	for (i = 0; i < perf_loops; i++)
+		node = rb_first_cached(&root);
+
+	time2 = get_cycles();
+	time = time2 - time1;
+
+	time = div_u64(time, perf_loops);
+	printk("        cached: %llu cycles\n", (unsigned long long)time);
+
+	for (i = 0; i < nnodes; i++)
+		erase(nodes + i, &root);
+
+	/* run checks */
+	for (i = 0; i < check_loops; i++) {
+		init();
+		for (j = 0; j < nnodes; j++) {
+			check(j);
+			insert(nodes + j, &root);
+		}
+		for (j = 0; j < nnodes; j++) {
+			check(nnodes - j);
+			erase(nodes + j, &root);
+		}
+		check(0);
+	}
+
+	return 0;
+}
+
+static int augmented_check(void)
+{
+	int i, j;
+	cycles_t time1, time2, time;
+
+	printk(KERN_ALERT "augmented rbtree testing");
+
+	init();
+
+	time1 = get_cycles();
+
+	for (i = 0; i < perf_loops; i++) {
+		for (j = 0; j < nnodes; j++)
+			insert_augmented(nodes + j, &root);
+		for (j = 0; j < nnodes; j++)
+			erase_augmented(nodes + j, &root);
+	}
+
+	time2 = get_cycles();
+	time = time2 - time1;
+
+	time = div_u64(time, perf_loops);
+	printk(" -> test 1 (latency of nnodes insert+delete): %llu cycles\n", (unsigned long long)time);
+
+	time1 = get_cycles();
+
+	for (i = 0; i < perf_loops; i++) {
+		for (j = 0; j < nnodes; j++)
+			insert_augmented_cached(nodes + j, &root);
+		for (j = 0; j < nnodes; j++)
+			erase_augmented_cached(nodes + j, &root);
+	}
+
+	time2 = get_cycles();
+	time = time2 - time1;
+
+	time = div_u64(time, perf_loops);
+	printk(" -> test 2 (latency of nnodes cached insert+delete): %llu cycles\n", (unsigned long long)time);
+
+	for (i = 0; i < check_loops; i++) {
+		init();
+		for (j = 0; j < nnodes; j++) {
+			check_augmented(j);
+			insert_augmented(nodes + j, &root);
+		}
+		for (j = 0; j < nnodes; j++) {
+			check_augmented(nnodes - j);
+			erase_augmented(nodes + j, &root);
+		}
+		check_augmented(0);
+	}
+
+	return 0;
+}
+
+static int __init rbtree_test_init(void)
+{
+	nodes = kmalloc_objs(*nodes, nnodes);
+	if (!nodes)
+		return -ENOMEM;
+
+	prandom_seed_state(&rnd, seed);
+
+	basic_check();
+	augmented_check();
+
+	kfree(nodes);
+
+	return -EAGAIN; /* Fail will directly unload the module */
+}
+
+static void __exit rbtree_test_exit(void)
+{
+	printk(KERN_ALERT "test exit\n");
+}
+
+module_init(rbtree_test_init)
+module_exit(rbtree_test_exit)
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Michel Lespinasse");
+MODULE_DESCRIPTION("Red Black Tree test");