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, 330 insertions, 0 deletions

diff --git a/tools/testing/radix-tree/main.c b/tools/testing/radix-tree/main.c
new file mode 100644
index 000000000..f2cbc8e5b
--- /dev/null
+++ b/tools/testing/radix-tree/main.c
@@ -0,0 +1,330 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <time.h>
+#include <assert.h>
+#include <limits.h>
+
+#include <linux/slab.h>
+#include <linux/radix-tree.h>
+
+#include "test.h"
+#include "regression.h"
+
+void __gang_check(unsigned long middle, long down, long up, int chunk, int hop)
+{
+	long idx;
+	RADIX_TREE(tree, GFP_KERNEL);
+
+	middle = 1 << 30;
+
+	for (idx = -down; idx < up; idx++)
+		item_insert(&tree, middle + idx);
+
+	item_check_absent(&tree, middle - down - 1);
+	for (idx = -down; idx < up; idx++)
+		item_check_present(&tree, middle + idx);
+	item_check_absent(&tree, middle + up);
+
+	if (chunk > 0) {
+		item_gang_check_present(&tree, middle - down, up + down,
+				chunk, hop);
+		item_full_scan(&tree, middle - down, down + up, chunk);
+	}
+	item_kill_tree(&tree);
+}
+
+void gang_check(void)
+{
+	__gang_check(1UL << 30, 128, 128, 35, 2);
+	__gang_check(1UL << 31, 128, 128, 32, 32);
+	__gang_check(1UL << 31, 128, 128, 32, 100);
+	__gang_check(1UL << 31, 128, 128, 17, 7);
+	__gang_check(0xffff0000UL, 0, 65536, 17, 7);
+	__gang_check(0xfffffffeUL, 1, 1, 17, 7);
+}
+
+void __big_gang_check(void)
+{
+	unsigned long start;
+	int wrapped = 0;
+
+	start = 0;
+	do {
+		unsigned long old_start;
+
+//		printf("0x%08lx\n", start);
+		__gang_check(start, rand() % 113 + 1, rand() % 71,
+				rand() % 157, rand() % 91 + 1);
+		old_start = start;
+		start += rand() % 1000000;
+		start %= 1ULL << 33;
+		if (start < old_start)
+			wrapped = 1;
+	} while (!wrapped);
+}
+
+void big_gang_check(bool long_run)
+{
+	int i;
+
+	for (i = 0; i < (long_run ? 1000 : 3); i++) {
+		__big_gang_check();
+		printv(2, "%d ", i);
+		fflush(stdout);
+	}
+}
+
+void add_and_check(void)
+{
+	RADIX_TREE(tree, GFP_KERNEL);
+
+	item_insert(&tree, 44);
+	item_check_present(&tree, 44);
+	item_check_absent(&tree, 43);
+	item_kill_tree(&tree);
+}
+
+void dynamic_height_check(void)
+{
+	int i;
+	RADIX_TREE(tree, GFP_KERNEL);
+	tree_verify_min_height(&tree, 0);
+
+	item_insert(&tree, 42);
+	tree_verify_min_height(&tree, 42);
+
+	item_insert(&tree, 1000000);
+	tree_verify_min_height(&tree, 1000000);
+
+	assert(item_delete(&tree, 1000000));
+	tree_verify_min_height(&tree, 42);
+
+	assert(item_delete(&tree, 42));
+	tree_verify_min_height(&tree, 0);
+
+	for (i = 0; i < 1000; i++) {
+		item_insert(&tree, i);
+		tree_verify_min_height(&tree, i);
+	}
+
+	i--;
+	for (;;) {
+		assert(item_delete(&tree, i));
+		if (i == 0) {
+			tree_verify_min_height(&tree, 0);
+			break;
+		}
+		i--;
+		tree_verify_min_height(&tree, i);
+	}
+
+	item_kill_tree(&tree);
+}
+
+void check_copied_tags(struct radix_tree_root *tree, unsigned long start, unsigned long end, unsigned long *idx, int count, int fromtag, int totag)
+{
+	int i;
+
+	for (i = 0; i < count; i++) {
+/*		if (i % 1000 == 0)
+			putchar('.'); */
+		if (idx[i] < start || idx[i] > end) {
+			if (item_tag_get(tree, idx[i], totag)) {
+				printv(2, "%lu-%lu: %lu, tags %d-%d\n", start,
+				       end, idx[i], item_tag_get(tree, idx[i],
+								 fromtag),
+				       item_tag_get(tree, idx[i], totag));
+			}
+			assert(!item_tag_get(tree, idx[i], totag));
+			continue;
+		}
+		if (item_tag_get(tree, idx[i], fromtag) ^
+			item_tag_get(tree, idx[i], totag)) {
+			printv(2, "%lu-%lu: %lu, tags %d-%d\n", start, end,
+			       idx[i], item_tag_get(tree, idx[i], fromtag),
+			       item_tag_get(tree, idx[i], totag));
+		}
+		assert(!(item_tag_get(tree, idx[i], fromtag) ^
+			 item_tag_get(tree, idx[i], totag)));
+	}
+}
+
+#define ITEMS 50000
+
+void copy_tag_check(void)
+{
+	RADIX_TREE(tree, GFP_KERNEL);
+	unsigned long idx[ITEMS];
+	unsigned long start, end, count = 0, tagged, cur, tmp;
+	int i;
+
+//	printf("generating radix tree indices...\n");
+	start = rand();
+	end = rand();
+	if (start > end && (rand() % 10)) {
+		cur = start;
+		start = end;
+		end = cur;
+	}
+	/* Specifically create items around the start and the end of the range
+	 * with high probability to check for off by one errors */
+	cur = rand();
+	if (cur & 1) {
+		item_insert(&tree, start);
+		if (cur & 2) {
+			if (start <= end)
+				count++;
+			item_tag_set(&tree, start, 0);
+		}
+	}
+	if (cur & 4) {
+		item_insert(&tree, start-1);
+		if (cur & 8)
+			item_tag_set(&tree, start-1, 0);
+	}
+	if (cur & 16) {
+		item_insert(&tree, end);
+		if (cur & 32) {
+			if (start <= end)
+				count++;
+			item_tag_set(&tree, end, 0);
+		}
+	}
+	if (cur & 64) {
+		item_insert(&tree, end+1);
+		if (cur & 128)
+			item_tag_set(&tree, end+1, 0);
+	}
+
+	for (i = 0; i < ITEMS; i++) {
+		do {
+			idx[i] = rand();
+		} while (item_lookup(&tree, idx[i]));
+
+		item_insert(&tree, idx[i]);
+		if (rand() & 1) {
+			item_tag_set(&tree, idx[i], 0);
+			if (idx[i] >= start && idx[i] <= end)
+				count++;
+		}
+/*		if (i % 1000 == 0)
+			putchar('.'); */
+	}
+
+//	printf("\ncopying tags...\n");
+	tagged = tag_tagged_items(&tree, start, end, ITEMS, XA_MARK_0, XA_MARK_1);
+
+//	printf("checking copied tags\n");
+	assert(tagged == count);
+	check_copied_tags(&tree, start, end, idx, ITEMS, 0, 1);
+
+	/* Copy tags in several rounds */
+//	printf("\ncopying tags...\n");
+	tmp = rand() % (count / 10 + 2);
+	tagged = tag_tagged_items(&tree, start, end, tmp, XA_MARK_0, XA_MARK_2);
+	assert(tagged == count);
+
+//	printf("%lu %lu %lu\n", tagged, tmp, count);
+//	printf("checking copied tags\n");
+	check_copied_tags(&tree, start, end, idx, ITEMS, 0, 2);
+	verify_tag_consistency(&tree, 0);
+	verify_tag_consistency(&tree, 1);
+	verify_tag_consistency(&tree, 2);
+//	printf("\n");
+	item_kill_tree(&tree);
+}
+
+static void single_thread_tests(bool long_run)
+{
+	int i;
+
+	printv(1, "starting single_thread_tests: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+	multiorder_checks();
+	rcu_barrier();
+	printv(2, "after multiorder_check: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+	tag_check();
+	rcu_barrier();
+	printv(2, "after tag_check: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+	gang_check();
+	rcu_barrier();
+	printv(2, "after gang_check: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+	add_and_check();
+	rcu_barrier();
+	printv(2, "after add_and_check: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+	dynamic_height_check();
+	rcu_barrier();
+	printv(2, "after dynamic_height_check: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+	idr_checks();
+	ida_tests();
+	rcu_barrier();
+	printv(2, "after idr_checks: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+	big_gang_check(long_run);
+	rcu_barrier();
+	printv(2, "after big_gang_check: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+	for (i = 0; i < (long_run ? 2000 : 3); i++) {
+		copy_tag_check();
+		printv(2, "%d ", i);
+		fflush(stdout);
+	}
+	rcu_barrier();
+	printv(2, "after copy_tag_check: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+}
+
+int main(int argc, char **argv)
+{
+	bool long_run = false;
+	int opt;
+	unsigned int seed = time(NULL);
+
+	while ((opt = getopt(argc, argv, "ls:v")) != -1) {
+		if (opt == 'l')
+			long_run = true;
+		else if (opt == 's')
+			seed = strtoul(optarg, NULL, 0);
+		else if (opt == 'v')
+			test_verbose++;
+	}
+
+	printf("random seed %u\n", seed);
+	srand(seed);
+
+	printf("running tests\n");
+
+	rcu_register_thread();
+	radix_tree_init();
+
+	xarray_tests();
+	regression1_test();
+	regression2_test();
+	regression3_test();
+	regression4_test();
+	iteration_test(0, 10 + 90 * long_run);
+	iteration_test(7, 10 + 90 * long_run);
+	iteration_test2(10 + 90 * long_run);
+	single_thread_tests(long_run);
+
+	/* Free any remaining preallocated nodes */
+	radix_tree_cpu_dead(0);
+
+	benchmark();
+
+	rcu_barrier();
+	printv(2, "after rcu_barrier: %d allocated, preempt %d\n",
+		nr_allocated, preempt_count);
+	rcu_unregister_thread();
+
+	printf("tests completed\n");
+
+	exit(0);
+}