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>

3 files changed, 189 insertions, 0 deletions

diff --git a/drivers/input/tests/.kunitconfig b/drivers/input/tests/.kunitconfig
new file mode 100644
index 000000000..2f5bedf80
--- /dev/null
+++ b/drivers/input/tests/.kunitconfig
@@ -0,0 +1,3 @@
+CONFIG_KUNIT=y
+CONFIG_INPUT=y
+CONFIG_INPUT_KUNIT_TEST=y
diff --git a/drivers/input/tests/Makefile b/drivers/input/tests/Makefile
new file mode 100644
index 000000000..90cf95418
--- /dev/null
+++ b/drivers/input/tests/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_INPUT_KUNIT_TEST) += input_test.o
diff --git a/drivers/input/tests/input_test.c b/drivers/input/tests/input_test.c
new file mode 100644
index 000000000..e105ce71a
--- /dev/null
+++ b/drivers/input/tests/input_test.c
@@ -0,0 +1,183 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for the input core.
+ *
+ * Copyright (c) 2023 Red Hat Inc
+ */
+
+#include <linux/delay.h>
+#include <linux/input.h>
+
+#include <kunit/test.h>
+
+#define POLL_INTERVAL 100
+
+static int input_test_init(struct kunit *test)
+{
+	struct input_dev *input_dev;
+	int ret;
+
+	input_dev = input_allocate_device();
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, input_dev);
+
+	input_dev->name = "Test input device";
+	input_dev->id.bustype = BUS_VIRTUAL;
+	input_dev->id.vendor = 1;
+	input_dev->id.product = 1;
+	input_dev->id.version = 1;
+	input_set_capability(input_dev, EV_KEY, BTN_LEFT);
+	input_set_capability(input_dev, EV_KEY, BTN_RIGHT);
+
+	ret = input_register_device(input_dev);
+	if (ret) {
+		input_free_device(input_dev);
+		KUNIT_FAIL_AND_ABORT(test, "Register device failed: %d", ret);
+	}
+
+	test->priv = input_dev;
+
+	return 0;
+}
+
+static void input_test_exit(struct kunit *test)
+{
+	struct input_dev *input_dev = test->priv;
+
+	if (input_dev)
+		input_unregister_device(input_dev);
+}
+
+static void input_test_poll(struct input_dev *input) { }
+
+static void input_test_polling(struct kunit *test)
+{
+	struct input_dev *input_dev = test->priv;
+
+	/* Must fail because a poll handler has not been set-up yet */
+	KUNIT_ASSERT_EQ(test, input_get_poll_interval(input_dev), -EINVAL);
+
+	KUNIT_ASSERT_EQ(test, input_setup_polling(input_dev, input_test_poll), 0);
+
+	input_set_poll_interval(input_dev, POLL_INTERVAL);
+
+	/* Must succeed because poll handler was set-up and poll interval set */
+	KUNIT_ASSERT_EQ(test, input_get_poll_interval(input_dev), POLL_INTERVAL);
+}
+
+static void input_test_timestamp(struct kunit *test)
+{
+	const ktime_t invalid_timestamp = ktime_set(0, 0);
+	struct input_dev *input_dev = test->priv;
+	ktime_t *timestamp, time;
+
+	timestamp = input_get_timestamp(input_dev);
+	time = timestamp[INPUT_CLK_MONO];
+
+	/* The returned timestamp must always be valid */
+	KUNIT_ASSERT_EQ(test, ktime_compare(time, invalid_timestamp), 1);
+
+	time = ktime_get();
+	input_set_timestamp(input_dev, time);
+
+	timestamp = input_get_timestamp(input_dev);
+	/* The timestamp must be the same than set before */
+	KUNIT_ASSERT_EQ(test, ktime_compare(timestamp[INPUT_CLK_MONO], time), 0);
+}
+
+static void input_test_match_device_id(struct kunit *test)
+{
+	struct input_dev *input_dev = test->priv;
+	struct input_device_id id = { 0 };
+
+	/*
+	 * Must match when the input device bus, vendor, product, version
+	 * and events capable of handling are the same and fail to match
+	 * otherwise.
+	 */
+	id.flags = INPUT_DEVICE_ID_MATCH_BUS;
+	id.bustype = BUS_VIRTUAL;
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	id.bustype = BUS_I2C;
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+
+	id.flags = INPUT_DEVICE_ID_MATCH_VENDOR;
+	id.vendor = 1;
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	id.vendor = 2;
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+
+	id.flags = INPUT_DEVICE_ID_MATCH_PRODUCT;
+	id.product = 1;
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	id.product = 2;
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+
+	id.flags = INPUT_DEVICE_ID_MATCH_VERSION;
+	id.version = 1;
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	id.version = 2;
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+
+	id.flags = INPUT_DEVICE_ID_MATCH_EVBIT;
+	__set_bit(EV_KEY, id.evbit);
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	__set_bit(EV_ABS, id.evbit);
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+}
+
+static void input_test_grab(struct kunit *test)
+{
+	struct input_dev *input_dev = test->priv;
+	struct input_handle test_handle;
+	struct input_handler handler;
+	struct input_handle handle;
+	struct input_device_id id;
+	int res;
+
+	handler.name = "handler";
+	handler.id_table = &id;
+
+	handle.dev = input_get_device(input_dev);
+	handle.name = dev_name(&input_dev->dev);
+	handle.handler = &handler;
+	res = input_grab_device(&handle);
+	KUNIT_ASSERT_TRUE(test, res == 0);
+
+	test_handle.dev = input_get_device(input_dev);
+	test_handle.name = dev_name(&input_dev->dev);
+	test_handle.handler = &handler;
+	res = input_grab_device(&test_handle);
+	KUNIT_ASSERT_EQ(test, res, -EBUSY);
+
+	input_release_device(&handle);
+	input_put_device(input_dev);
+	res = input_grab_device(&test_handle);
+	KUNIT_ASSERT_TRUE(test, res == 0);
+	input_put_device(input_dev);
+}
+
+static struct kunit_case input_tests[] = {
+	KUNIT_CASE(input_test_polling),
+	KUNIT_CASE(input_test_timestamp),
+	KUNIT_CASE(input_test_match_device_id),
+	KUNIT_CASE(input_test_grab),
+	{ /* sentinel */ }
+};
+
+static struct kunit_suite input_test_suite = {
+	.name = "input_core",
+	.init = input_test_init,
+	.exit = input_test_exit,
+	.test_cases = input_tests,
+};
+
+kunit_test_suite(input_test_suite);
+
+MODULE_AUTHOR("Javier Martinez Canillas <javierm@redhat.com>");
+MODULE_DESCRIPTION("KUnit test for the input core");
+MODULE_LICENSE("GPL");