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, 130 insertions, 0 deletions

diff --git a/drivers/input/misc/ab8500-ponkey.c b/drivers/input/misc/ab8500-ponkey.c
new file mode 100644
index 000000000..a9b901368
--- /dev/null
+++ b/drivers/input/misc/ab8500-ponkey.c
@@ -0,0 +1,130 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) ST-Ericsson SA 2010
+ *
+ * Author: Sundar Iyer <sundar.iyer@stericsson.com> for ST-Ericsson
+ *
+ * AB8500 Power-On Key handler
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/abx500/ab8500.h>
+#include <linux/of.h>
+#include <linux/slab.h>
+
+/**
+ * struct ab8500_ponkey - ab8500 ponkey information
+ * @idev: pointer to input device
+ * @ab8500: ab8500 parent
+ * @irq_dbf: irq number for falling transition
+ * @irq_dbr: irq number for rising transition
+ */
+struct ab8500_ponkey {
+	struct input_dev	*idev;
+	struct ab8500		*ab8500;
+	int			irq_dbf;
+	int			irq_dbr;
+};
+
+/* AB8500 gives us an interrupt when ONKEY is held */
+static irqreturn_t ab8500_ponkey_handler(int irq, void *data)
+{
+	struct ab8500_ponkey *ponkey = data;
+
+	if (irq == ponkey->irq_dbf)
+		input_report_key(ponkey->idev, KEY_POWER, true);
+	else if (irq == ponkey->irq_dbr)
+		input_report_key(ponkey->idev, KEY_POWER, false);
+
+	input_sync(ponkey->idev);
+
+	return IRQ_HANDLED;
+}
+
+static int ab8500_ponkey_probe(struct platform_device *pdev)
+{
+	struct ab8500 *ab8500 = dev_get_drvdata(pdev->dev.parent);
+	struct ab8500_ponkey *ponkey;
+	struct input_dev *input;
+	int irq_dbf, irq_dbr;
+	int error;
+
+	irq_dbf = platform_get_irq_byname(pdev, "ONKEY_DBF");
+	if (irq_dbf < 0)
+		return irq_dbf;
+
+	irq_dbr = platform_get_irq_byname(pdev, "ONKEY_DBR");
+	if (irq_dbr < 0)
+		return irq_dbr;
+
+	ponkey = devm_kzalloc(&pdev->dev, sizeof(struct ab8500_ponkey),
+			      GFP_KERNEL);
+	if (!ponkey)
+		return -ENOMEM;
+
+	input = devm_input_allocate_device(&pdev->dev);
+	if (!input)
+		return -ENOMEM;
+
+	ponkey->idev = input;
+	ponkey->ab8500 = ab8500;
+	ponkey->irq_dbf = irq_dbf;
+	ponkey->irq_dbr = irq_dbr;
+
+	input->name = "AB8500 POn(PowerOn) Key";
+	input->dev.parent = &pdev->dev;
+
+	input_set_capability(input, EV_KEY, KEY_POWER);
+
+	error = devm_request_any_context_irq(&pdev->dev, ponkey->irq_dbf,
+					     ab8500_ponkey_handler, 0,
+					     "ab8500-ponkey-dbf", ponkey);
+	if (error < 0) {
+		dev_err(ab8500->dev, "Failed to request dbf IRQ#%d: %d\n",
+			ponkey->irq_dbf, error);
+		return error;
+	}
+
+	error = devm_request_any_context_irq(&pdev->dev, ponkey->irq_dbr,
+					     ab8500_ponkey_handler, 0,
+					     "ab8500-ponkey-dbr", ponkey);
+	if (error < 0) {
+		dev_err(ab8500->dev, "Failed to request dbr IRQ#%d: %d\n",
+			ponkey->irq_dbr, error);
+		return error;
+	}
+
+	error = input_register_device(ponkey->idev);
+	if (error) {
+		dev_err(ab8500->dev, "Can't register input device: %d\n", error);
+		return error;
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id ab8500_ponkey_match[] = {
+	{ .compatible = "stericsson,ab8500-ponkey", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, ab8500_ponkey_match);
+#endif
+
+static struct platform_driver ab8500_ponkey_driver = {
+	.driver		= {
+		.name	= "ab8500-poweron-key",
+		.of_match_table = of_match_ptr(ab8500_ponkey_match),
+	},
+	.probe		= ab8500_ponkey_probe,
+};
+module_platform_driver(ab8500_ponkey_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Sundar Iyer <sundar.iyer@stericsson.com>");
+MODULE_DESCRIPTION("ST-Ericsson AB8500 Power-ON(Pon) Key driver");