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, 156 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/ipaq-micro-ts.c b/drivers/input/touchscreen/ipaq-micro-ts.c
new file mode 100644
index 000000000..243e6465d
--- /dev/null
+++ b/drivers/input/touchscreen/ipaq-micro-ts.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * h3600 atmel micro companion support, touchscreen subdevice
+ * Author : Alessandro Gardich <gremlin@gremlin.it>
+ * Author : Dmitry Artamonow <mad_soft@inbox.ru>
+ * Author : Linus Walleij <linus.walleij@linaro.org>
+ */
+
+#include <asm/byteorder.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/pm.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/input.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/mfd/ipaq-micro.h>
+
+struct touchscreen_data {
+	struct input_dev *input;
+	struct ipaq_micro *micro;
+};
+
+static void micro_ts_receive(void *data, int len, unsigned char *msg)
+{
+	struct touchscreen_data *ts = data;
+
+	if (len == 4) {
+		input_report_abs(ts->input, ABS_X,
+				 be16_to_cpup((__be16 *) &msg[2]));
+		input_report_abs(ts->input, ABS_Y,
+				 be16_to_cpup((__be16 *) &msg[0]));
+		input_report_key(ts->input, BTN_TOUCH, 1);
+		input_sync(ts->input);
+	} else if (len == 0) {
+		input_report_abs(ts->input, ABS_X, 0);
+		input_report_abs(ts->input, ABS_Y, 0);
+		input_report_key(ts->input, BTN_TOUCH, 0);
+		input_sync(ts->input);
+	}
+}
+
+static void micro_ts_toggle_receive(struct touchscreen_data *ts, bool enable)
+{
+	struct ipaq_micro *micro = ts->micro;
+
+	guard(spinlock_irq)(&micro->lock);
+
+	if (enable) {
+		micro->ts = micro_ts_receive;
+		micro->ts_data = ts;
+	} else {
+		micro->ts = NULL;
+		micro->ts_data = NULL;
+	}
+}
+
+static int micro_ts_open(struct input_dev *input)
+{
+	struct touchscreen_data *ts = input_get_drvdata(input);
+
+	micro_ts_toggle_receive(ts, true);
+
+	return 0;
+}
+
+static void micro_ts_close(struct input_dev *input)
+{
+	struct touchscreen_data *ts = input_get_drvdata(input);
+
+	micro_ts_toggle_receive(ts, false);
+}
+
+static int micro_ts_probe(struct platform_device *pdev)
+{
+	struct ipaq_micro *micro = dev_get_drvdata(pdev->dev.parent);
+	struct touchscreen_data *ts;
+	int error;
+
+	ts = devm_kzalloc(&pdev->dev, sizeof(*ts), GFP_KERNEL);
+	if (!ts)
+		return -ENOMEM;
+
+	ts->micro = micro;
+
+	ts->input = devm_input_allocate_device(&pdev->dev);
+	if (!ts->input) {
+		dev_err(&pdev->dev, "failed to allocate input device\n");
+		return -ENOMEM;
+	}
+
+	ts->input->name = "ipaq micro ts";
+	ts->input->open = micro_ts_open;
+	ts->input->close = micro_ts_close;
+
+	input_set_drvdata(ts->input, ts);
+
+	input_set_capability(ts->input, EV_KEY, BTN_TOUCH);
+	input_set_capability(ts->input, EV_ABS, ABS_X);
+	input_set_capability(ts->input, EV_ABS, ABS_Y);
+	input_set_abs_params(ts->input, ABS_X, 0, 1023, 0, 0);
+	input_set_abs_params(ts->input, ABS_Y, 0, 1023, 0, 0);
+
+	error = input_register_device(ts->input);
+	if (error) {
+		dev_err(&pdev->dev, "error registering touch input\n");
+		return error;
+	}
+
+	platform_set_drvdata(pdev, ts);
+
+	dev_info(&pdev->dev, "iPAQ micro touchscreen\n");
+
+	return 0;
+}
+
+static int micro_ts_suspend(struct device *dev)
+{
+	struct touchscreen_data *ts = dev_get_drvdata(dev);
+
+	micro_ts_toggle_receive(ts, false);
+
+	return 0;
+}
+
+static int micro_ts_resume(struct device *dev)
+{
+	struct touchscreen_data *ts = dev_get_drvdata(dev);
+	struct input_dev *input = ts->input;
+
+	guard(mutex)(&input->mutex);
+
+	if (input_device_enabled(input))
+		micro_ts_toggle_receive(ts, true);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(micro_ts_dev_pm_ops,
+				micro_ts_suspend, micro_ts_resume);
+
+static struct platform_driver micro_ts_device_driver = {
+	.driver	= {
+		.name	= "ipaq-micro-ts",
+		.pm	= pm_sleep_ptr(&micro_ts_dev_pm_ops),
+	},
+	.probe	= micro_ts_probe,
+};
+module_platform_driver(micro_ts_device_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("driver for iPAQ Atmel micro touchscreen");
+MODULE_ALIAS("platform:ipaq-micro-ts");