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, 143 insertions, 0 deletions

diff --git a/drivers/mfd/madera-i2c.c b/drivers/mfd/madera-i2c.c
new file mode 100644
index 000000000..0986e4a99
--- /dev/null
+++ b/drivers/mfd/madera-i2c.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * I2C bus interface to Cirrus Logic Madera codecs
+ *
+ * Copyright (C) 2015-2018 Cirrus Logic
+ */
+
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+
+#include <linux/mfd/madera/core.h>
+
+#include "madera.h"
+
+static int madera_i2c_probe(struct i2c_client *i2c)
+{
+	struct madera *madera;
+	const struct regmap_config *regmap_16bit_config = NULL;
+	const struct regmap_config *regmap_32bit_config = NULL;
+	unsigned long type;
+	const char *name;
+	int ret;
+
+	type = (uintptr_t)i2c_get_match_data(i2c);
+	switch (type) {
+	case CS47L15:
+		if (IS_ENABLED(CONFIG_MFD_CS47L15)) {
+			regmap_16bit_config = &cs47l15_16bit_i2c_regmap;
+			regmap_32bit_config = &cs47l15_32bit_i2c_regmap;
+		}
+		break;
+	case CS47L35:
+		if (IS_ENABLED(CONFIG_MFD_CS47L35)) {
+			regmap_16bit_config = &cs47l35_16bit_i2c_regmap;
+			regmap_32bit_config = &cs47l35_32bit_i2c_regmap;
+		}
+		break;
+	case CS47L85:
+	case WM1840:
+		if (IS_ENABLED(CONFIG_MFD_CS47L85)) {
+			regmap_16bit_config = &cs47l85_16bit_i2c_regmap;
+			regmap_32bit_config = &cs47l85_32bit_i2c_regmap;
+		}
+		break;
+	case CS47L90:
+	case CS47L91:
+		if (IS_ENABLED(CONFIG_MFD_CS47L90)) {
+			regmap_16bit_config = &cs47l90_16bit_i2c_regmap;
+			regmap_32bit_config = &cs47l90_32bit_i2c_regmap;
+		}
+		break;
+	case CS42L92:
+	case CS47L92:
+	case CS47L93:
+		if (IS_ENABLED(CONFIG_MFD_CS47L92)) {
+			regmap_16bit_config = &cs47l92_16bit_i2c_regmap;
+			regmap_32bit_config = &cs47l92_32bit_i2c_regmap;
+		}
+		break;
+	default:
+		dev_err(&i2c->dev,
+			"Unknown Madera I2C device type %ld\n", type);
+		return -EINVAL;
+	}
+
+	name = madera_name_from_type(type);
+
+	if (!regmap_16bit_config) {
+		/* it's polite to say which codec isn't built into the kernel */
+		dev_err(&i2c->dev,
+			"Kernel does not include support for %s\n", name);
+		return -EINVAL;
+	}
+
+	madera = devm_kzalloc(&i2c->dev, sizeof(*madera), GFP_KERNEL);
+	if (!madera)
+		return -ENOMEM;
+
+	madera->regmap = devm_regmap_init_i2c(i2c, regmap_16bit_config);
+	if (IS_ERR(madera->regmap)) {
+		ret = PTR_ERR(madera->regmap);
+		dev_err(&i2c->dev,
+			"Failed to allocate 16-bit register map: %d\n",	ret);
+		return ret;
+	}
+
+	madera->regmap_32bit = devm_regmap_init_i2c(i2c, regmap_32bit_config);
+	if (IS_ERR(madera->regmap_32bit)) {
+		ret = PTR_ERR(madera->regmap_32bit);
+		dev_err(&i2c->dev,
+			"Failed to allocate 32-bit register map: %d\n", ret);
+		return ret;
+	}
+
+	madera->type = type;
+	madera->type_name = name;
+	madera->dev = &i2c->dev;
+	madera->irq = i2c->irq;
+
+	return madera_dev_init(madera);
+}
+
+static void madera_i2c_remove(struct i2c_client *i2c)
+{
+	struct madera *madera = dev_get_drvdata(&i2c->dev);
+
+	madera_dev_exit(madera);
+}
+
+static const struct i2c_device_id madera_i2c_id[] = {
+	{ "cs47l15", CS47L15 },
+	{ "cs47l35", CS47L35 },
+	{ "cs47l85", CS47L85 },
+	{ "cs47l90", CS47L90 },
+	{ "cs47l91", CS47L91 },
+	{ "cs42l92", CS42L92 },
+	{ "cs47l92", CS47L92 },
+	{ "cs47l93", CS47L93 },
+	{ "wm1840", WM1840 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, madera_i2c_id);
+
+static struct i2c_driver madera_i2c_driver = {
+	.driver = {
+		.name	= "madera",
+		.pm	= &madera_pm_ops,
+		.of_match_table	= of_match_ptr(madera_of_match),
+	},
+	.probe		= madera_i2c_probe,
+	.remove		= madera_i2c_remove,
+	.id_table	= madera_i2c_id,
+};
+
+module_i2c_driver(madera_i2c_driver);
+
+MODULE_DESCRIPTION("Madera I2C bus interface");
+MODULE_AUTHOR("Richard Fitzgerald <rf@opensource.cirrus.com>");
+MODULE_LICENSE("GPL v2");