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, 376 insertions, 0 deletions

diff --git a/tools/testing/shared/linux.c b/tools/testing/shared/linux.c
new file mode 100644
index 000000000..e0a0693df
--- /dev/null
+++ b/tools/testing/shared/linux.c
@@ -0,0 +1,376 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdlib.h>
+#include <string.h>
+#include <malloc.h>
+#include <pthread.h>
+#include <unistd.h>
+#include <assert.h>
+
+#include <linux/gfp.h>
+#include <linux/poison.h>
+#include <linux/slab.h>
+#include <linux/radix-tree.h>
+#include <urcu/uatomic.h>
+
+int nr_allocated;
+int preempt_count;
+int test_verbose;
+
+void kmem_cache_set_callback(struct kmem_cache *cachep, void (*callback)(void *))
+{
+	cachep->callback = callback;
+}
+
+void kmem_cache_set_private(struct kmem_cache *cachep, void *private)
+{
+	cachep->private = private;
+}
+
+void kmem_cache_set_non_kernel(struct kmem_cache *cachep, unsigned int val)
+{
+	cachep->non_kernel = val;
+}
+
+unsigned long kmem_cache_get_alloc(struct kmem_cache *cachep)
+{
+	return cachep->size * cachep->nr_allocated;
+}
+
+unsigned long kmem_cache_nr_allocated(struct kmem_cache *cachep)
+{
+	return cachep->nr_allocated;
+}
+
+unsigned long kmem_cache_nr_tallocated(struct kmem_cache *cachep)
+{
+	return cachep->nr_tallocated;
+}
+
+void kmem_cache_zero_nr_tallocated(struct kmem_cache *cachep)
+{
+	cachep->nr_tallocated = 0;
+}
+
+void *kmem_cache_alloc_lru(struct kmem_cache *cachep, struct list_lru *lru,
+		int gfp)
+{
+	void *p;
+
+	if (cachep->exec_callback) {
+		if (cachep->callback)
+			cachep->callback(cachep->private);
+		cachep->exec_callback = false;
+	}
+
+	if (!(gfp & __GFP_DIRECT_RECLAIM)) {
+		if (!cachep->non_kernel) {
+			if (cachep->callback)
+				cachep->exec_callback = true;
+			return NULL;
+		}
+
+		cachep->non_kernel--;
+	}
+
+	pthread_mutex_lock(&cachep->lock);
+	if (cachep->nr_objs) {
+		struct radix_tree_node *node = cachep->objs;
+		cachep->nr_objs--;
+		cachep->objs = node->parent;
+		pthread_mutex_unlock(&cachep->lock);
+		node->parent = NULL;
+		p = node;
+	} else {
+		pthread_mutex_unlock(&cachep->lock);
+		if (cachep->align) {
+			if (posix_memalign(&p, cachep->align, cachep->size) < 0)
+				return NULL;
+		} else {
+			p = malloc(cachep->size);
+		}
+
+		if (cachep->ctor)
+			cachep->ctor(p);
+		else if (gfp & __GFP_ZERO)
+			memset(p, 0, cachep->size);
+	}
+
+	uatomic_inc(&cachep->nr_allocated);
+	uatomic_inc(&nr_allocated);
+	uatomic_inc(&cachep->nr_tallocated);
+	if (kmalloc_verbose)
+		printf("Allocating %p from slab\n", p);
+	return p;
+}
+
+void __kmem_cache_free_locked(struct kmem_cache *cachep, void *objp)
+{
+	assert(objp);
+	if (cachep->nr_objs > 10 || cachep->align) {
+		memset(objp, POISON_FREE, cachep->size);
+		free(objp);
+	} else {
+		struct radix_tree_node *node = objp;
+		cachep->nr_objs++;
+		node->parent = cachep->objs;
+		cachep->objs = node;
+	}
+}
+
+void kmem_cache_free_locked(struct kmem_cache *cachep, void *objp)
+{
+	uatomic_dec(&nr_allocated);
+	uatomic_dec(&cachep->nr_allocated);
+	if (kmalloc_verbose)
+		printf("Freeing %p to slab\n", objp);
+	__kmem_cache_free_locked(cachep, objp);
+}
+
+void kmem_cache_free(struct kmem_cache *cachep, void *objp)
+{
+	pthread_mutex_lock(&cachep->lock);
+	kmem_cache_free_locked(cachep, objp);
+	pthread_mutex_unlock(&cachep->lock);
+}
+
+void kmem_cache_free_bulk(struct kmem_cache *cachep, size_t size, void **list)
+{
+	if (kmalloc_verbose)
+		pr_debug("Bulk free %p[0-%zu]\n", list, size - 1);
+
+	if (cachep->exec_callback) {
+		if (cachep->callback)
+			cachep->callback(cachep->private);
+		cachep->exec_callback = false;
+	}
+
+	pthread_mutex_lock(&cachep->lock);
+	for (int i = 0; i < size; i++)
+		kmem_cache_free_locked(cachep, list[i]);
+	pthread_mutex_unlock(&cachep->lock);
+}
+
+void kmem_cache_shrink(struct kmem_cache *cachep)
+{
+}
+
+bool kmem_cache_alloc_bulk(struct kmem_cache *cachep, gfp_t gfp, size_t size,
+			  void **p)
+{
+	size_t i;
+
+	if (kmalloc_verbose)
+		pr_debug("Bulk alloc %zu\n", size);
+
+	pthread_mutex_lock(&cachep->lock);
+	if (cachep->nr_objs >= size) {
+		struct radix_tree_node *node;
+
+		for (i = 0; i < size; i++) {
+			if (!(gfp & __GFP_DIRECT_RECLAIM)) {
+				if (!cachep->non_kernel)
+					break;
+				cachep->non_kernel--;
+			}
+
+			node = cachep->objs;
+			cachep->nr_objs--;
+			cachep->objs = node->parent;
+			p[i] = node;
+			node->parent = NULL;
+		}
+		pthread_mutex_unlock(&cachep->lock);
+	} else {
+		pthread_mutex_unlock(&cachep->lock);
+		for (i = 0; i < size; i++) {
+			if (!(gfp & __GFP_DIRECT_RECLAIM)) {
+				if (!cachep->non_kernel)
+					break;
+				cachep->non_kernel--;
+			}
+
+			if (cachep->align) {
+				if (posix_memalign(&p[i], cachep->align,
+					       cachep->size) < 0)
+					break;
+			} else {
+				p[i] = malloc(cachep->size);
+				if (!p[i])
+					break;
+			}
+			if (cachep->ctor)
+				cachep->ctor(p[i]);
+			else if (gfp & __GFP_ZERO)
+				memset(p[i], 0, cachep->size);
+		}
+	}
+
+	if (i < size) {
+		size = i;
+		pthread_mutex_lock(&cachep->lock);
+		for (i = 0; i < size; i++)
+			__kmem_cache_free_locked(cachep, p[i]);
+		pthread_mutex_unlock(&cachep->lock);
+		if (cachep->callback)
+			cachep->exec_callback = true;
+		return false;
+	}
+
+	for (i = 0; i < size; i++) {
+		uatomic_inc(&nr_allocated);
+		uatomic_inc(&cachep->nr_allocated);
+		uatomic_inc(&cachep->nr_tallocated);
+		if (kmalloc_verbose)
+			printf("Allocating %p from slab\n", p[i]);
+	}
+
+	return true;
+}
+
+struct kmem_cache *
+__kmem_cache_create_args(const char *name, unsigned int size,
+			  struct kmem_cache_args *args,
+			  unsigned int flags)
+{
+	struct kmem_cache *ret = malloc(sizeof(*ret));
+
+	pthread_mutex_init(&ret->lock, NULL);
+	ret->size = size;
+	ret->align = args->align;
+	ret->sheaf_capacity = args->sheaf_capacity;
+	ret->nr_objs = 0;
+	ret->nr_allocated = 0;
+	ret->nr_tallocated = 0;
+	ret->objs = NULL;
+	ret->ctor = args->ctor;
+	ret->non_kernel = 0;
+	ret->exec_callback = false;
+	ret->callback = NULL;
+	ret->private = NULL;
+
+	return ret;
+}
+
+struct slab_sheaf *
+kmem_cache_prefill_sheaf(struct kmem_cache *s, gfp_t gfp, unsigned int size)
+{
+	struct slab_sheaf *sheaf;
+	unsigned int capacity;
+
+	if (s->exec_callback) {
+		if (s->callback)
+			s->callback(s->private);
+		s->exec_callback = false;
+	}
+
+	capacity = max(size, s->sheaf_capacity);
+
+	sheaf = calloc(1, sizeof(*sheaf) + sizeof(void *) * capacity);
+	if (!sheaf)
+		return NULL;
+
+	sheaf->cache = s;
+	sheaf->capacity = capacity;
+	sheaf->size = size;
+	if (!kmem_cache_alloc_bulk(s, gfp, size, sheaf->objects)) {
+		free(sheaf);
+		return NULL;
+	}
+
+	return sheaf;
+}
+
+int kmem_cache_refill_sheaf(struct kmem_cache *s, gfp_t gfp,
+		 struct slab_sheaf **sheafp, unsigned int size)
+{
+	struct slab_sheaf *sheaf = *sheafp;
+
+	if (sheaf->size >= size)
+		return 0;
+
+	if (size > sheaf->capacity) {
+		sheaf = kmem_cache_prefill_sheaf(s, gfp, size);
+		if (!sheaf)
+			return -ENOMEM;
+
+		kmem_cache_return_sheaf(s, gfp, *sheafp);
+		*sheafp = sheaf;
+		return 0;
+	}
+
+	if (!kmem_cache_alloc_bulk(s, gfp, size - sheaf->size,
+			&sheaf->objects[sheaf->size]))
+		return -ENOMEM;
+	sheaf->size = size;
+	return 0;
+}
+
+void kmem_cache_return_sheaf(struct kmem_cache *s, gfp_t gfp,
+		 struct slab_sheaf *sheaf)
+{
+	if (sheaf->size)
+		kmem_cache_free_bulk(s, sheaf->size, &sheaf->objects[0]);
+
+	free(sheaf);
+}
+
+void *
+kmem_cache_alloc_from_sheaf(struct kmem_cache *s, gfp_t gfp,
+		struct slab_sheaf *sheaf)
+{
+	void *obj;
+
+	if (sheaf->size == 0) {
+		printf("Nothing left in sheaf!\n");
+		return NULL;
+	}
+
+	obj = sheaf->objects[--sheaf->size];
+	sheaf->objects[sheaf->size] = NULL;
+
+	return obj;
+}
+
+/*
+ * Test the test infrastructure for kem_cache_alloc/free and bulk counterparts.
+ */
+void test_kmem_cache_bulk(void)
+{
+	int i;
+	void *list[12];
+	static struct kmem_cache *test_cache, *test_cache2;
+
+	/*
+	 * Testing the bulk allocators without aligned kmem_cache to force the
+	 * bulk alloc/free to reuse
+	 */
+	test_cache = kmem_cache_create("test_cache", 256, 0, SLAB_PANIC, NULL);
+
+	for (i = 0; i < 5; i++)
+		list[i] = kmem_cache_alloc(test_cache, __GFP_DIRECT_RECLAIM);
+
+	for (i = 0; i < 5; i++)
+		kmem_cache_free(test_cache, list[i]);
+	assert(test_cache->nr_objs == 5);
+
+	kmem_cache_alloc_bulk(test_cache, __GFP_DIRECT_RECLAIM, 5, list);
+	kmem_cache_free_bulk(test_cache, 5, list);
+
+	for (i = 0; i < 12 ; i++)
+		list[i] = kmem_cache_alloc(test_cache, __GFP_DIRECT_RECLAIM);
+
+	for (i = 0; i < 12; i++)
+		kmem_cache_free(test_cache, list[i]);
+
+	/* The last free will not be kept around */
+	assert(test_cache->nr_objs == 11);
+
+	/* Aligned caches will immediately free */
+	test_cache2 = kmem_cache_create("test_cache2", 128, 128, SLAB_PANIC, NULL);
+
+	kmem_cache_alloc_bulk(test_cache2, __GFP_DIRECT_RECLAIM, 10, list);
+	kmem_cache_free_bulk(test_cache2, 10, list);
+	assert(!test_cache2->nr_objs);
+
+
+}