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, 148 insertions, 0 deletions

diff --git a/drivers/input/misc/wm831x-on.c b/drivers/input/misc/wm831x-on.c
new file mode 100644
index 000000000..18eb319bc
--- /dev/null
+++ b/drivers/input/misc/wm831x-on.c
@@ -0,0 +1,148 @@
+/*
+ * wm831x-on.c - WM831X ON pin driver
+ *
+ * Copyright (C) 2009 Wolfson Microelectronics plc
+ *
+ * This file is subject to the terms and conditions of the GNU General
+ * Public License. See the file "COPYING" in the main directory of this
+ * archive for more details.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/platform_device.h>
+#include <linux/workqueue.h>
+#include <linux/mfd/wm831x/core.h>
+
+struct wm831x_on {
+	struct input_dev *dev;
+	struct delayed_work work;
+	struct wm831x *wm831x;
+};
+
+/*
+ * The chip gives us an interrupt when the ON pin is asserted but we
+ * then need to poll to see when the pin is deasserted.
+ */
+static void wm831x_poll_on(struct work_struct *work)
+{
+	struct wm831x_on *wm831x_on = container_of(work, struct wm831x_on,
+						   work.work);
+	struct wm831x *wm831x = wm831x_on->wm831x;
+	int poll, ret;
+
+	ret = wm831x_reg_read(wm831x, WM831X_ON_PIN_CONTROL);
+	if (ret >= 0) {
+		poll = !(ret & WM831X_ON_PIN_STS);
+
+		input_report_key(wm831x_on->dev, KEY_POWER, poll);
+		input_sync(wm831x_on->dev);
+	} else {
+		dev_err(wm831x->dev, "Failed to read ON status: %d\n", ret);
+		poll = 1;
+	}
+
+	if (poll)
+		schedule_delayed_work(&wm831x_on->work, 100);
+}
+
+static irqreturn_t wm831x_on_irq(int irq, void *data)
+{
+	struct wm831x_on *wm831x_on = data;
+
+	schedule_delayed_work(&wm831x_on->work, 0);
+
+	return IRQ_HANDLED;
+}
+
+static int wm831x_on_probe(struct platform_device *pdev)
+{
+	struct wm831x *wm831x = dev_get_drvdata(pdev->dev.parent);
+	struct wm831x_on *wm831x_on;
+	int irq = wm831x_irq(wm831x, platform_get_irq(pdev, 0));
+	int ret;
+
+	wm831x_on = devm_kzalloc(&pdev->dev, sizeof(struct wm831x_on),
+				 GFP_KERNEL);
+	if (!wm831x_on) {
+		dev_err(&pdev->dev, "Can't allocate data\n");
+		return -ENOMEM;
+	}
+
+	wm831x_on->wm831x = wm831x;
+	INIT_DELAYED_WORK(&wm831x_on->work, wm831x_poll_on);
+
+	wm831x_on->dev = devm_input_allocate_device(&pdev->dev);
+	if (!wm831x_on->dev) {
+		dev_err(&pdev->dev, "Can't allocate input dev\n");
+		ret = -ENOMEM;
+		goto err;
+	}
+
+	wm831x_on->dev->evbit[0] = BIT_MASK(EV_KEY);
+	wm831x_on->dev->keybit[BIT_WORD(KEY_POWER)] = BIT_MASK(KEY_POWER);
+	wm831x_on->dev->name = "wm831x_on";
+	wm831x_on->dev->phys = "wm831x_on/input0";
+	wm831x_on->dev->dev.parent = &pdev->dev;
+
+	ret = request_threaded_irq(irq, NULL, wm831x_on_irq,
+				   IRQF_TRIGGER_RISING | IRQF_ONESHOT,
+				   "wm831x_on",
+				   wm831x_on);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "Unable to request IRQ: %d\n", ret);
+		goto err_input_dev;
+	}
+	ret = input_register_device(wm831x_on->dev);
+	if (ret) {
+		dev_dbg(&pdev->dev, "Can't register input device: %d\n", ret);
+		goto err_irq;
+	}
+
+	platform_set_drvdata(pdev, wm831x_on);
+
+	return 0;
+
+err_irq:
+	free_irq(irq, wm831x_on);
+err_input_dev:
+err:
+	return ret;
+}
+
+static void wm831x_on_remove(struct platform_device *pdev)
+{
+	struct wm831x_on *wm831x_on = platform_get_drvdata(pdev);
+	int irq = platform_get_irq(pdev, 0);
+
+	free_irq(irq, wm831x_on);
+	cancel_delayed_work_sync(&wm831x_on->work);
+}
+
+static struct platform_driver wm831x_on_driver = {
+	.probe		= wm831x_on_probe,
+	.remove		= wm831x_on_remove,
+	.driver		= {
+		.name	= "wm831x-on",
+	},
+};
+module_platform_driver(wm831x_on_driver);
+
+MODULE_ALIAS("platform:wm831x-on");
+MODULE_DESCRIPTION("WM831x ON pin");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Mark Brown <broonie@opensource.wolfsonmicro.com>");
+