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, 144 insertions, 0 deletions

diff --git a/drivers/mfd/simple-mfd-i2c.c b/drivers/mfd/simple-mfd-i2c.c
new file mode 100644
index 000000000..ef3ce4bdf
--- /dev/null
+++ b/drivers/mfd/simple-mfd-i2c.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Simple MFD - I2C
+ *
+ * Author(s):
+ * 	Michael Walle <michael@walle.cc>
+ * 	Lee Jones <lee.jones@linaro.org>
+ *
+ * This driver creates a single register map with the intention for it to be
+ * shared by all sub-devices.  Children can use their parent's device structure
+ * (dev.parent) in order to reference it.
+ *
+ * Once the register map has been successfully initialised, any sub-devices
+ * represented by child nodes in Device Tree or via the MFD cells in this file
+ * will be subsequently registered.
+ */
+
+#include <linux/array_size.h>
+#include <linux/dev_printk.h>
+#include <linux/err.h>
+#include <linux/i2c.h>
+#include <linux/mfd/core.h>
+#include <linux/module.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/property.h>
+#include <linux/regmap.h>
+#include <linux/stddef.h>
+
+#include "simple-mfd-i2c.h"
+
+static const struct regmap_config regmap_config_8r_8v = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
+static int simple_mfd_i2c_probe(struct i2c_client *i2c)
+{
+	const struct simple_mfd_data *simple_mfd_data;
+	const struct regmap_config *regmap_config;
+	struct regmap *regmap;
+	int ret;
+
+	simple_mfd_data = device_get_match_data(&i2c->dev);
+
+	/* If no regmap_config is specified, use the default 8reg and 8val bits */
+	if (!simple_mfd_data || !simple_mfd_data->regmap_config)
+		regmap_config = &regmap_config_8r_8v;
+	else
+		regmap_config = simple_mfd_data->regmap_config;
+
+	regmap = devm_regmap_init_i2c(i2c, regmap_config);
+	if (IS_ERR(regmap))
+		return PTR_ERR(regmap);
+
+	/* If no MFD cells are specified, register using the DT child nodes instead */
+	if (!simple_mfd_data || !simple_mfd_data->mfd_cell)
+		return devm_of_platform_populate(&i2c->dev);
+
+	ret = devm_mfd_add_devices(&i2c->dev, PLATFORM_DEVID_AUTO,
+				   simple_mfd_data->mfd_cell,
+				   simple_mfd_data->mfd_cell_size,
+				   NULL, 0, NULL);
+	if (ret)
+		dev_err(&i2c->dev, "Failed to add child devices\n");
+
+	return ret;
+}
+
+static const struct mfd_cell sy7636a_cells[] = {
+	{ .name = "sy7636a-regulator", },
+	{ .name = "sy7636a-temperature", },
+};
+
+static const struct simple_mfd_data silergy_sy7636a = {
+	.mfd_cell = sy7636a_cells,
+	.mfd_cell_size = ARRAY_SIZE(sy7636a_cells),
+};
+
+static const struct mfd_cell max5970_cells[] = {
+	{ .name = "max5970-regulator", },
+	{ .name = "max5970-iio", },
+	{ .name = "max5970-led", },
+};
+
+static const struct simple_mfd_data maxim_max5970 = {
+	.mfd_cell = max5970_cells,
+	.mfd_cell_size = ARRAY_SIZE(max5970_cells),
+};
+
+static const struct mfd_cell max77705_sensor_cells[] = {
+	{ .name = "max77705-battery" },
+	{ .name = "max77705-hwmon", },
+};
+
+static const struct simple_mfd_data maxim_mon_max77705 = {
+	.mfd_cell = max77705_sensor_cells,
+	.mfd_cell_size = ARRAY_SIZE(max77705_sensor_cells),
+};
+
+static const struct regmap_config spacemit_p1_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
+static const struct mfd_cell spacemit_p1_cells[] = {
+	{ .name = "spacemit-p1-reboot", },
+	{ .name = "spacemit-p1-regulator", },
+	{ .name = "spacemit-p1-rtc", },
+};
+
+static const struct simple_mfd_data spacemit_p1 = {
+	.regmap_config = &spacemit_p1_regmap_config,
+	.mfd_cell = spacemit_p1_cells,
+	.mfd_cell_size = ARRAY_SIZE(spacemit_p1_cells),
+};
+
+static const struct of_device_id simple_mfd_i2c_of_match[] = {
+	{ .compatible = "delta,tn48m-cpld" },
+	{ .compatible = "fsl,ls1028aqds-fpga" },
+	{ .compatible = "fsl,lx2160aqds-fpga" },
+	{ .compatible = "fsl,lx2160ardb-fpga" },
+	{ .compatible = "kontron,sl28cpld" },
+	{ .compatible = "maxim,max5970", .data = &maxim_max5970 },
+	{ .compatible = "maxim,max5978", .data = &maxim_max5970 },
+	{ .compatible = "maxim,max77705-battery", .data = &maxim_mon_max77705 },
+	{ .compatible = "silergy,sy7636a", .data = &silergy_sy7636a },
+	{ .compatible = "spacemit,p1", .data = &spacemit_p1 },
+	{}
+};
+MODULE_DEVICE_TABLE(of, simple_mfd_i2c_of_match);
+
+static struct i2c_driver simple_mfd_i2c_driver = {
+	.probe = simple_mfd_i2c_probe,
+	.driver = {
+		.name = "simple-mfd-i2c",
+		.of_match_table = simple_mfd_i2c_of_match,
+	},
+};
+module_i2c_driver(simple_mfd_i2c_driver);
+
+MODULE_AUTHOR("Michael Walle <michael@walle.cc>");
+MODULE_DESCRIPTION("Simple MFD - I2C driver");
+MODULE_LICENSE("GPL v2");