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, 395 insertions, 0 deletions

diff --git a/lib/test_parman.c b/lib/test_parman.c
new file mode 100644
index 000000000..28f095118
--- /dev/null
+++ b/lib/test_parman.c
@@ -0,0 +1,395 @@
+/*
+ * lib/test_parman.c - Test module for parman
+ * Copyright (c) 2017 Mellanox Technologies. All rights reserved.
+ * Copyright (c) 2017 Jiri Pirko <jiri@mellanox.com>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the names of the copyright holders nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * Alternatively, this software may be distributed under the terms of the
+ * GNU General Public License ("GPL") version 2 as published by the Free
+ * Software Foundation.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/bitops.h>
+#include <linux/err.h>
+#include <linux/prandom.h>
+#include <linux/parman.h>
+
+#define TEST_PARMAN_PRIO_SHIFT 7 /* defines number of prios for testing */
+#define TEST_PARMAN_PRIO_COUNT BIT(TEST_PARMAN_PRIO_SHIFT)
+#define TEST_PARMAN_PRIO_MASK (TEST_PARMAN_PRIO_COUNT - 1)
+
+#define TEST_PARMAN_ITEM_SHIFT 13 /* defines a total number
+				   * of items for testing
+				   */
+#define TEST_PARMAN_ITEM_COUNT BIT(TEST_PARMAN_ITEM_SHIFT)
+#define TEST_PARMAN_ITEM_MASK (TEST_PARMAN_ITEM_COUNT - 1)
+
+#define TEST_PARMAN_BASE_SHIFT 8
+#define TEST_PARMAN_BASE_COUNT BIT(TEST_PARMAN_BASE_SHIFT)
+#define TEST_PARMAN_RESIZE_STEP_SHIFT 7
+#define TEST_PARMAN_RESIZE_STEP_COUNT BIT(TEST_PARMAN_RESIZE_STEP_SHIFT)
+
+#define TEST_PARMAN_BULK_MAX_SHIFT (2 + TEST_PARMAN_RESIZE_STEP_SHIFT)
+#define TEST_PARMAN_BULK_MAX_COUNT BIT(TEST_PARMAN_BULK_MAX_SHIFT)
+#define TEST_PARMAN_BULK_MAX_MASK (TEST_PARMAN_BULK_MAX_COUNT - 1)
+
+#define TEST_PARMAN_RUN_BUDGET (TEST_PARMAN_ITEM_COUNT * 256)
+
+struct test_parman_prio {
+	struct parman_prio parman_prio;
+	unsigned long priority;
+};
+
+struct test_parman_item {
+	struct parman_item parman_item;
+	struct test_parman_prio *prio;
+	bool used;
+};
+
+struct test_parman {
+	struct parman *parman;
+	struct test_parman_item **prio_array;
+	unsigned long prio_array_limit;
+	struct test_parman_prio prios[TEST_PARMAN_PRIO_COUNT];
+	struct test_parman_item items[TEST_PARMAN_ITEM_COUNT];
+	struct rnd_state rnd;
+	unsigned long run_budget;
+	unsigned long bulk_budget;
+	bool bulk_noop;
+	unsigned int used_items;
+};
+
+#define ITEM_PTRS_SIZE(count) (sizeof(struct test_parman_item *) * (count))
+
+static int test_parman_resize(void *priv, unsigned long new_count)
+{
+	struct test_parman *test_parman = priv;
+	struct test_parman_item **prio_array;
+	unsigned long old_count;
+
+	prio_array = krealloc(test_parman->prio_array,
+			      ITEM_PTRS_SIZE(new_count), GFP_KERNEL);
+	if (new_count == 0)
+		return 0;
+	if (!prio_array)
+		return -ENOMEM;
+	old_count = test_parman->prio_array_limit;
+	if (new_count > old_count)
+		memset(&prio_array[old_count], 0,
+		       ITEM_PTRS_SIZE(new_count - old_count));
+	test_parman->prio_array = prio_array;
+	test_parman->prio_array_limit = new_count;
+	return 0;
+}
+
+static void test_parman_move(void *priv, unsigned long from_index,
+			     unsigned long to_index, unsigned long count)
+{
+	struct test_parman *test_parman = priv;
+	struct test_parman_item **prio_array = test_parman->prio_array;
+
+	memmove(&prio_array[to_index], &prio_array[from_index],
+		ITEM_PTRS_SIZE(count));
+	memset(&prio_array[from_index], 0, ITEM_PTRS_SIZE(count));
+}
+
+static const struct parman_ops test_parman_lsort_ops = {
+	.base_count	= TEST_PARMAN_BASE_COUNT,
+	.resize_step	= TEST_PARMAN_RESIZE_STEP_COUNT,
+	.resize		= test_parman_resize,
+	.move		= test_parman_move,
+	.algo		= PARMAN_ALGO_TYPE_LSORT,
+};
+
+static void test_parman_rnd_init(struct test_parman *test_parman)
+{
+	prandom_seed_state(&test_parman->rnd, 3141592653589793238ULL);
+}
+
+static u32 test_parman_rnd_get(struct test_parman *test_parman)
+{
+	return prandom_u32_state(&test_parman->rnd);
+}
+
+static unsigned long test_parman_priority_gen(struct test_parman *test_parman)
+{
+	unsigned long priority;
+	int i;
+
+again:
+	priority = test_parman_rnd_get(test_parman);
+	if (priority == 0)
+		goto again;
+
+	for (i = 0; i < TEST_PARMAN_PRIO_COUNT; i++) {
+		struct test_parman_prio *prio = &test_parman->prios[i];
+
+		if (prio->priority == 0)
+			break;
+		if (prio->priority == priority)
+			goto again;
+	}
+	return priority;
+}
+
+static void test_parman_prios_init(struct test_parman *test_parman)
+{
+	int i;
+
+	for (i = 0; i < TEST_PARMAN_PRIO_COUNT; i++) {
+		struct test_parman_prio *prio = &test_parman->prios[i];
+
+		/* Assign random uniqueue priority to each prio structure */
+		prio->priority = test_parman_priority_gen(test_parman);
+		parman_prio_init(test_parman->parman, &prio->parman_prio,
+				 prio->priority);
+	}
+}
+
+static void test_parman_prios_fini(struct test_parman *test_parman)
+{
+	int i;
+
+	for (i = 0; i < TEST_PARMAN_PRIO_COUNT; i++) {
+		struct test_parman_prio *prio = &test_parman->prios[i];
+
+		parman_prio_fini(&prio->parman_prio);
+	}
+}
+
+static void test_parman_items_init(struct test_parman *test_parman)
+{
+	int i;
+
+	for (i = 0; i < TEST_PARMAN_ITEM_COUNT; i++) {
+		struct test_parman_item *item = &test_parman->items[i];
+		unsigned int prio_index = test_parman_rnd_get(test_parman) &
+					  TEST_PARMAN_PRIO_MASK;
+
+		/* Assign random prio to each item structure */
+		item->prio = &test_parman->prios[prio_index];
+	}
+}
+
+static void test_parman_items_fini(struct test_parman *test_parman)
+{
+	int i;
+
+	for (i = 0; i < TEST_PARMAN_ITEM_COUNT; i++) {
+		struct test_parman_item *item = &test_parman->items[i];
+
+		if (!item->used)
+			continue;
+		parman_item_remove(test_parman->parman,
+				   &item->prio->parman_prio,
+				   &item->parman_item);
+	}
+}
+
+static struct test_parman *test_parman_create(const struct parman_ops *ops)
+{
+	struct test_parman *test_parman;
+	int err;
+
+	test_parman = kzalloc_obj(*test_parman);
+	if (!test_parman)
+		return ERR_PTR(-ENOMEM);
+	err = test_parman_resize(test_parman, TEST_PARMAN_BASE_COUNT);
+	if (err)
+		goto err_resize;
+	test_parman->parman = parman_create(ops, test_parman);
+	if (!test_parman->parman) {
+		err = -ENOMEM;
+		goto err_parman_create;
+	}
+	test_parman_rnd_init(test_parman);
+	test_parman_prios_init(test_parman);
+	test_parman_items_init(test_parman);
+	test_parman->run_budget = TEST_PARMAN_RUN_BUDGET;
+	return test_parman;
+
+err_parman_create:
+	test_parman_resize(test_parman, 0);
+err_resize:
+	kfree(test_parman);
+	return ERR_PTR(err);
+}
+
+static void test_parman_destroy(struct test_parman *test_parman)
+{
+	test_parman_items_fini(test_parman);
+	test_parman_prios_fini(test_parman);
+	parman_destroy(test_parman->parman);
+	test_parman_resize(test_parman, 0);
+	kfree(test_parman);
+}
+
+static bool test_parman_run_check_budgets(struct test_parman *test_parman)
+{
+	if (test_parman->run_budget-- == 0)
+		return false;
+	if (test_parman->bulk_budget-- != 0)
+		return true;
+
+	test_parman->bulk_budget = test_parman_rnd_get(test_parman) &
+				   TEST_PARMAN_BULK_MAX_MASK;
+	test_parman->bulk_noop = test_parman_rnd_get(test_parman) & 1;
+	return true;
+}
+
+static int test_parman_run(struct test_parman *test_parman)
+{
+	unsigned int i = test_parman_rnd_get(test_parman);
+	int err;
+
+	while (test_parman_run_check_budgets(test_parman)) {
+		unsigned int item_index = i++ & TEST_PARMAN_ITEM_MASK;
+		struct test_parman_item *item = &test_parman->items[item_index];
+
+		if (test_parman->bulk_noop)
+			continue;
+
+		if (!item->used) {
+			err = parman_item_add(test_parman->parman,
+					      &item->prio->parman_prio,
+					      &item->parman_item);
+			if (err)
+				return err;
+			test_parman->prio_array[item->parman_item.index] = item;
+			test_parman->used_items++;
+		} else {
+			test_parman->prio_array[item->parman_item.index] = NULL;
+			parman_item_remove(test_parman->parman,
+					   &item->prio->parman_prio,
+					   &item->parman_item);
+			test_parman->used_items--;
+		}
+		item->used = !item->used;
+	}
+	return 0;
+}
+
+static int test_parman_check_array(struct test_parman *test_parman,
+				   bool gaps_allowed)
+{
+	unsigned int last_unused_items = 0;
+	unsigned long last_priority = 0;
+	unsigned int used_items = 0;
+	int i;
+
+	if (test_parman->prio_array_limit < TEST_PARMAN_BASE_COUNT) {
+		pr_err("Array limit is lower than the base count (%lu < %lu)\n",
+		       test_parman->prio_array_limit, TEST_PARMAN_BASE_COUNT);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < test_parman->prio_array_limit; i++) {
+		struct test_parman_item *item = test_parman->prio_array[i];
+
+		if (!item) {
+			last_unused_items++;
+			continue;
+		}
+		if (last_unused_items && !gaps_allowed) {
+			pr_err("Gap found in array even though they are forbidden\n");
+			return -EINVAL;
+		}
+
+		last_unused_items = 0;
+		used_items++;
+
+		if (item->prio->priority < last_priority) {
+			pr_err("Item belongs under higher priority then the last one (current: %lu, previous: %lu)\n",
+			       item->prio->priority, last_priority);
+			return -EINVAL;
+		}
+		last_priority = item->prio->priority;
+
+		if (item->parman_item.index != i) {
+			pr_err("Item has different index in compare to where it actually is (%lu != %d)\n",
+			       item->parman_item.index, i);
+			return -EINVAL;
+		}
+	}
+
+	if (used_items != test_parman->used_items) {
+		pr_err("Number of used items in array does not match (%u != %u)\n",
+		       used_items, test_parman->used_items);
+		return -EINVAL;
+	}
+
+	if (last_unused_items >= TEST_PARMAN_RESIZE_STEP_COUNT) {
+		pr_err("Number of unused item at the end of array is bigger than resize step (%u >= %lu)\n",
+		       last_unused_items, TEST_PARMAN_RESIZE_STEP_COUNT);
+		return -EINVAL;
+	}
+
+	pr_info("Priority array check successful\n");
+
+	return 0;
+}
+
+static int test_parman_lsort(void)
+{
+	struct test_parman *test_parman;
+	int err;
+
+	test_parman = test_parman_create(&test_parman_lsort_ops);
+	if (IS_ERR(test_parman))
+		return PTR_ERR(test_parman);
+
+	err = test_parman_run(test_parman);
+	if (err)
+		goto out;
+
+	err = test_parman_check_array(test_parman, false);
+	if (err)
+		goto out;
+out:
+	test_parman_destroy(test_parman);
+	return err;
+}
+
+static int __init test_parman_init(void)
+{
+	return test_parman_lsort();
+}
+
+static void __exit test_parman_exit(void)
+{
+}
+
+module_init(test_parman_init);
+module_exit(test_parman_exit);
+
+MODULE_LICENSE("Dual BSD/GPL");
+MODULE_AUTHOR("Jiri Pirko <jiri@mellanox.com>");
+MODULE_DESCRIPTION("Test module for parman");