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, 163 insertions, 0 deletions

diff --git a/drivers/input/misc/twl4030-pwrbutton.c b/drivers/input/misc/twl4030-pwrbutton.c
new file mode 100644
index 000000000..3e94a5995
--- /dev/null
+++ b/drivers/input/misc/twl4030-pwrbutton.c
@@ -0,0 +1,163 @@
+/*
+ * TWL4030 Power Button Input Driver
+ *
+ * Copyright (C) 2008-2009 Nokia Corporation
+ *
+ * Written by Peter De Schrijver <peter.de-schrijver@nokia.com>
+ * Several fixes by Felipe Balbi <felipe.balbi@nokia.com>
+ *
+ * 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/bits.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/property.h>
+#include <linux/platform_device.h>
+#include <linux/mfd/twl.h>
+
+#define PWR_PWRON_IRQ BIT(0)
+
+struct twl_pwrbutton_chipdata {
+	u8 status_reg;
+	bool need_manual_irq;
+};
+
+static const struct twl_pwrbutton_chipdata twl4030_chipdata = {
+	.status_reg = 0xf,
+	.need_manual_irq = false,
+};
+
+static const struct twl_pwrbutton_chipdata twl6030_chipdata = {
+	.status_reg = 0x2,
+	.need_manual_irq = true,
+};
+
+static irqreturn_t powerbutton_irq(int irq, void *_pwr)
+{
+	struct input_dev *pwr = _pwr;
+	const struct twl_pwrbutton_chipdata *pdata = dev_get_drvdata(pwr->dev.parent);
+	int err;
+	u8 value;
+
+	err = twl_i2c_read_u8(TWL_MODULE_PM_MASTER, &value, pdata->status_reg);
+	if (!err)  {
+		pm_wakeup_event(pwr->dev.parent, 0);
+		input_report_key(pwr, KEY_POWER, value & PWR_PWRON_IRQ);
+		input_sync(pwr);
+	} else {
+		dev_err(pwr->dev.parent, "twl4030: i2c error %d while reading"
+			" TWL4030 PM_MASTER STS_HW_CONDITIONS register\n", err);
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int twl4030_pwrbutton_probe(struct platform_device *pdev)
+{
+	const struct twl_pwrbutton_chipdata *pdata;
+	struct input_dev *pwr;
+	int irq = platform_get_irq(pdev, 0);
+	int err;
+
+	pdata = device_get_match_data(&pdev->dev);
+	if (!pdata)
+		return -EINVAL;
+
+	platform_set_drvdata(pdev, (void *)pdata);
+
+	pwr = devm_input_allocate_device(&pdev->dev);
+	if (!pwr) {
+		dev_err(&pdev->dev, "Can't allocate power button\n");
+		return -ENOMEM;
+	}
+
+	input_set_capability(pwr, EV_KEY, KEY_POWER);
+	pwr->name = "twl4030_pwrbutton";
+	pwr->phys = "twl4030_pwrbutton/input0";
+	pwr->dev.parent = &pdev->dev;
+
+	err = devm_request_threaded_irq(&pdev->dev, irq, NULL, powerbutton_irq,
+			IRQF_TRIGGER_FALLING | IRQF_TRIGGER_RISING |
+			IRQF_ONESHOT,
+			"twl4030_pwrbutton", pwr);
+	if (err < 0) {
+		dev_err(&pdev->dev, "Can't get IRQ for pwrbutton: %d\n", err);
+		return err;
+	}
+
+	err = input_register_device(pwr);
+	if (err) {
+		dev_err(&pdev->dev, "Can't register power button: %d\n", err);
+		return err;
+	}
+
+	if (pdata->need_manual_irq) {
+		err = twl6030_interrupt_unmask(0x01, REG_INT_MSK_LINE_A);
+		if (err)
+			return err;
+
+		err = twl6030_interrupt_unmask(0x01, REG_INT_MSK_STS_A);
+		if (err)
+			return err;
+	}
+
+	device_init_wakeup(&pdev->dev, true);
+
+	return 0;
+}
+
+static void twl4030_pwrbutton_remove(struct platform_device *pdev)
+{
+	const struct twl_pwrbutton_chipdata *pdata = platform_get_drvdata(pdev);
+
+	if (pdata->need_manual_irq) {
+		twl6030_interrupt_mask(0x01, REG_INT_MSK_LINE_A);
+		twl6030_interrupt_mask(0x01, REG_INT_MSK_STS_A);
+	}
+}
+
+static const struct of_device_id twl4030_pwrbutton_dt_match_table[] = {
+	{
+		.compatible = "ti,twl4030-pwrbutton",
+		.data = &twl4030_chipdata,
+	},
+	{
+		.compatible = "ti,twl6030-pwrbutton",
+		.data = &twl6030_chipdata,
+	},
+	{ }
+};
+MODULE_DEVICE_TABLE(of, twl4030_pwrbutton_dt_match_table);
+
+static struct platform_driver twl4030_pwrbutton_driver = {
+	.probe		= twl4030_pwrbutton_probe,
+	.remove		= twl4030_pwrbutton_remove,
+	.driver		= {
+		.name	= "twl4030_pwrbutton",
+		.of_match_table = twl4030_pwrbutton_dt_match_table,
+	},
+};
+module_platform_driver(twl4030_pwrbutton_driver);
+
+MODULE_ALIAS("platform:twl4030_pwrbutton");
+MODULE_DESCRIPTION("Triton2 Power Button");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Peter De Schrijver <peter.de-schrijver@nokia.com>");
+MODULE_AUTHOR("Felipe Balbi <felipe.balbi@nokia.com>");
+