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, 126 insertions, 0 deletions

diff --git a/drivers/mfd/lp87565.c b/drivers/mfd/lp87565.c
new file mode 100644
index 000000000..b78ae79df
--- /dev/null
+++ b/drivers/mfd/lp87565.c
@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2017 Texas Instruments Incorporated - https://www.ti.com/
+ *
+ * Author: Keerthy <j-keerthy@ti.com>
+ */
+
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/core.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+
+#include <linux/mfd/lp87565.h>
+
+static const struct regmap_config lp87565_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = LP87565_REG_MAX,
+};
+
+static const struct mfd_cell lp87565_cells[] = {
+	{ .name = "lp87565-q1-regulator", },
+	{ .name = "lp87565-q1-gpio", },
+};
+
+static const struct of_device_id of_lp87565_match_table[] = {
+	{ .compatible = "ti,lp87565", },
+	{
+		.compatible = "ti,lp87524-q1",
+		.data = (void *)LP87565_DEVICE_TYPE_LP87524_Q1,
+	},
+	{
+		.compatible = "ti,lp87565-q1",
+		.data = (void *)LP87565_DEVICE_TYPE_LP87565_Q1,
+	},
+	{
+		.compatible = "ti,lp87561-q1",
+		.data = (void *)LP87565_DEVICE_TYPE_LP87561_Q1,
+	},
+	{}
+};
+MODULE_DEVICE_TABLE(of, of_lp87565_match_table);
+
+static int lp87565_probe(struct i2c_client *client)
+{
+	struct lp87565 *lp87565;
+	int ret;
+	unsigned int otpid;
+
+	lp87565 = devm_kzalloc(&client->dev, sizeof(*lp87565), GFP_KERNEL);
+	if (!lp87565)
+		return -ENOMEM;
+
+	lp87565->dev = &client->dev;
+
+	lp87565->regmap = devm_regmap_init_i2c(client, &lp87565_regmap_config);
+	if (IS_ERR(lp87565->regmap)) {
+		ret = PTR_ERR(lp87565->regmap);
+		dev_err(lp87565->dev,
+			"Failed to initialize register map: %d\n", ret);
+		return ret;
+	}
+
+	lp87565->reset_gpio = devm_gpiod_get_optional(lp87565->dev, "reset",
+						      GPIOD_OUT_LOW);
+	if (IS_ERR(lp87565->reset_gpio)) {
+		ret = PTR_ERR(lp87565->reset_gpio);
+		if (ret == -EPROBE_DEFER)
+			return ret;
+	}
+
+	if (lp87565->reset_gpio) {
+		gpiod_set_value_cansleep(lp87565->reset_gpio, 1);
+		/* The minimum assertion time is undocumented, just guess */
+		usleep_range(2000, 4000);
+
+		gpiod_set_value_cansleep(lp87565->reset_gpio, 0);
+		/* Min 1.2 ms before first I2C transaction */
+		usleep_range(1500, 3000);
+	}
+
+	ret = regmap_read(lp87565->regmap, LP87565_REG_OTP_REV, &otpid);
+	if (ret) {
+		dev_err(lp87565->dev, "Failed to read OTP ID\n");
+		return ret;
+	}
+
+	lp87565->rev = otpid & LP87565_OTP_REV_OTP_ID;
+	lp87565->dev_type = (uintptr_t)i2c_get_match_data(client);
+
+	i2c_set_clientdata(client, lp87565);
+
+	return devm_mfd_add_devices(lp87565->dev, PLATFORM_DEVID_AUTO,
+				    lp87565_cells, ARRAY_SIZE(lp87565_cells),
+				    NULL, 0, NULL);
+}
+
+static void lp87565_shutdown(struct i2c_client *client)
+{
+	struct lp87565 *lp87565 = i2c_get_clientdata(client);
+
+	gpiod_set_value_cansleep(lp87565->reset_gpio, 1);
+}
+
+static const struct i2c_device_id lp87565_id_table[] = {
+	{ "lp87565-q1" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, lp87565_id_table);
+
+static struct i2c_driver lp87565_driver = {
+	.driver	= {
+		.name	= "lp87565",
+		.of_match_table = of_lp87565_match_table,
+	},
+	.probe = lp87565_probe,
+	.shutdown = lp87565_shutdown,
+	.id_table = lp87565_id_table,
+};
+module_i2c_driver(lp87565_driver);
+
+MODULE_AUTHOR("J Keerthy <j-keerthy@ti.com>");
+MODULE_DESCRIPTION("lp87565 chip family Multi-Function Device driver");
+MODULE_LICENSE("GPL v2");