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, 165 insertions, 0 deletions

diff --git a/drivers/input/keyboard/ipaq-micro-keys.c b/drivers/input/keyboard/ipaq-micro-keys.c
new file mode 100644
index 000000000..ebd991de7
--- /dev/null
+++ b/drivers/input/keyboard/ipaq-micro-keys.c
@@ -0,0 +1,165 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * h3600 atmel micro companion support, key subdevice
+ * based on previous kernel 2.4 version
+ * Author : Alessandro Gardich <gremlin@gremlin.it>
+ * Author : Linus Walleij <linus.walleij@linaro.org>
+ */
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <linux/pm.h>
+#include <linux/sysctl.h>
+#include <linux/proc_fs.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/input.h>
+#include <linux/platform_device.h>
+#include <linux/mfd/ipaq-micro.h>
+
+static const u16 micro_keycodes[] = {
+	KEY_RECORD,		/* 1:  Record button			*/
+	KEY_CALENDAR,		/* 2:  Calendar				*/
+	KEY_ADDRESSBOOK,	/* 3:  Contacts (looks like Outlook)	*/
+	KEY_MAIL,		/* 4:  Envelope (Q on older iPAQs)	*/
+	KEY_HOMEPAGE,		/* 5:  Start (looks like swoopy arrow)	*/
+	KEY_UP,			/* 6:  Up				*/
+	KEY_RIGHT,		/* 7:  Right				*/
+	KEY_LEFT,		/* 8:  Left				*/
+	KEY_DOWN,		/* 9:  Down				*/
+};
+
+struct ipaq_micro_keys {
+	struct ipaq_micro *micro;
+	struct input_dev *input;
+	u16 codes[ARRAY_SIZE(micro_keycodes)];
+};
+
+static void micro_key_receive(void *data, int len, unsigned char *msg)
+{
+	struct ipaq_micro_keys *keys = data;
+	int key, down;
+
+	if (len < 1)
+		return;
+
+	down = 0x80 & msg[0];
+	key  = 0x7f & msg[0];
+
+	if (key < ARRAY_SIZE(micro_keycodes)) {
+		input_report_key(keys->input, keys->codes[key], down);
+		input_sync(keys->input);
+	}
+}
+
+static void micro_key_start(struct ipaq_micro_keys *keys)
+{
+	guard(spinlock_irq)(&keys->micro->lock);
+
+	keys->micro->key = micro_key_receive;
+	keys->micro->key_data = keys;
+}
+
+static void micro_key_stop(struct ipaq_micro_keys *keys)
+{
+	guard(spinlock_irq)(&keys->micro->lock);
+
+	keys->micro->key = NULL;
+	keys->micro->key_data = NULL;
+}
+
+static int micro_key_open(struct input_dev *input)
+{
+	struct ipaq_micro_keys *keys = input_get_drvdata(input);
+
+	micro_key_start(keys);
+
+	return 0;
+}
+
+static void micro_key_close(struct input_dev *input)
+{
+	struct ipaq_micro_keys *keys = input_get_drvdata(input);
+
+	micro_key_stop(keys);
+}
+
+static int micro_key_probe(struct platform_device *pdev)
+{
+	struct ipaq_micro_keys *keys;
+	int error;
+	int i;
+
+	keys = devm_kzalloc(&pdev->dev, sizeof(*keys), GFP_KERNEL);
+	if (!keys)
+		return -ENOMEM;
+
+	keys->micro = dev_get_drvdata(pdev->dev.parent);
+
+	keys->input = devm_input_allocate_device(&pdev->dev);
+	if (!keys->input)
+		return -ENOMEM;
+
+	keys->input->keycodesize = sizeof(micro_keycodes[0]);
+	keys->input->keycodemax = ARRAY_SIZE(micro_keycodes);
+	memcpy(keys->codes, micro_keycodes, sizeof(keys->codes));
+
+	keys->input->keycode = keys->codes;
+
+	__set_bit(EV_KEY, keys->input->evbit);
+	for (i = 0; i < ARRAY_SIZE(micro_keycodes); i++)
+		__set_bit(micro_keycodes[i], keys->input->keybit);
+
+	keys->input->name = "h3600 micro keys";
+	keys->input->open = micro_key_open;
+	keys->input->close = micro_key_close;
+	input_set_drvdata(keys->input, keys);
+
+	error = input_register_device(keys->input);
+	if (error)
+		return error;
+
+	platform_set_drvdata(pdev, keys);
+	return 0;
+}
+
+static int micro_key_suspend(struct device *dev)
+{
+	struct ipaq_micro_keys *keys = dev_get_drvdata(dev);
+
+	micro_key_stop(keys);
+
+	return 0;
+}
+
+static int micro_key_resume(struct device *dev)
+{
+	struct ipaq_micro_keys *keys = dev_get_drvdata(dev);
+	struct input_dev *input = keys->input;
+
+	guard(mutex)(&input->mutex);
+
+	if (input_device_enabled(input))
+		micro_key_start(keys);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(micro_key_dev_pm_ops,
+				micro_key_suspend, micro_key_resume);
+
+static struct platform_driver micro_key_device_driver = {
+	.driver = {
+		.name    = "ipaq-micro-keys",
+		.pm	= pm_sleep_ptr(&micro_key_dev_pm_ops),
+	},
+	.probe   = micro_key_probe,
+};
+module_platform_driver(micro_key_device_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("driver for iPAQ Atmel micro keys");
+MODULE_ALIAS("platform:ipaq-micro-keys");