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, 238 insertions, 0 deletions

diff --git a/drivers/base/regmap/regmap-w1.c b/drivers/base/regmap/regmap-w1.c
new file mode 100644
index 000000000..29fd24f9c
--- /dev/null
+++ b/drivers/base/regmap/regmap-w1.c
@@ -0,0 +1,238 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Register map access API - W1 (1-Wire) support
+//
+// Copyright (c) 2017 Radioavionica Corporation
+// Author: Alex A. Mihaylov <minimumlaw@rambler.ru>
+
+#include <linux/regmap.h>
+#include <linux/module.h>
+#include <linux/w1.h>
+
+#include "internal.h"
+
+#define W1_CMD_READ_DATA	0x69
+#define W1_CMD_WRITE_DATA	0x6C
+
+/*
+ * 1-Wire slaves registers with addess 8 bit and data 8 bit
+ */
+
+static int w1_reg_a8_v8_read(void *context, unsigned int reg, unsigned int *val)
+{
+	struct device *dev = context;
+	struct w1_slave *sl = container_of(dev, struct w1_slave, dev);
+	int ret = 0;
+
+	if (reg > 255)
+		return -EINVAL;
+
+	mutex_lock(&sl->master->bus_mutex);
+	if (!w1_reset_select_slave(sl)) {
+		w1_write_8(sl->master, W1_CMD_READ_DATA);
+		w1_write_8(sl->master, reg);
+		*val = w1_read_8(sl->master);
+	} else {
+		ret = -ENODEV;
+	}
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return ret;
+}
+
+static int w1_reg_a8_v8_write(void *context, unsigned int reg, unsigned int val)
+{
+	struct device *dev = context;
+	struct w1_slave *sl = container_of(dev, struct w1_slave, dev);
+	int ret = 0;
+
+	if (reg > 255)
+		return -EINVAL;
+
+	mutex_lock(&sl->master->bus_mutex);
+	if (!w1_reset_select_slave(sl)) {
+		w1_write_8(sl->master, W1_CMD_WRITE_DATA);
+		w1_write_8(sl->master, reg);
+		w1_write_8(sl->master, val);
+	} else {
+		ret = -ENODEV;
+	}
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return ret;
+}
+
+/*
+ * 1-Wire slaves registers with addess 8 bit and data 16 bit
+ */
+
+static int w1_reg_a8_v16_read(void *context, unsigned int reg,
+				unsigned int *val)
+{
+	struct device *dev = context;
+	struct w1_slave *sl = container_of(dev, struct w1_slave, dev);
+	int ret = 0;
+
+	if (reg > 255)
+		return -EINVAL;
+
+	mutex_lock(&sl->master->bus_mutex);
+	if (!w1_reset_select_slave(sl)) {
+		w1_write_8(sl->master, W1_CMD_READ_DATA);
+		w1_write_8(sl->master, reg);
+		*val = w1_read_8(sl->master);
+		*val |= w1_read_8(sl->master)<<8;
+	} else {
+		ret = -ENODEV;
+	}
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return ret;
+}
+
+static int w1_reg_a8_v16_write(void *context, unsigned int reg,
+				unsigned int val)
+{
+	struct device *dev = context;
+	struct w1_slave *sl = container_of(dev, struct w1_slave, dev);
+	int ret = 0;
+
+	if (reg > 255)
+		return -EINVAL;
+
+	mutex_lock(&sl->master->bus_mutex);
+	if (!w1_reset_select_slave(sl)) {
+		w1_write_8(sl->master, W1_CMD_WRITE_DATA);
+		w1_write_8(sl->master, reg);
+		w1_write_8(sl->master, val & 0x00FF);
+		w1_write_8(sl->master, val>>8 & 0x00FF);
+	} else {
+		ret = -ENODEV;
+	}
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return ret;
+}
+
+/*
+ * 1-Wire slaves registers with addess 16 bit and data 16 bit
+ */
+
+static int w1_reg_a16_v16_read(void *context, unsigned int reg,
+				unsigned int *val)
+{
+	struct device *dev = context;
+	struct w1_slave *sl = container_of(dev, struct w1_slave, dev);
+	int ret = 0;
+
+	if (reg > 65535)
+		return -EINVAL;
+
+	mutex_lock(&sl->master->bus_mutex);
+	if (!w1_reset_select_slave(sl)) {
+		w1_write_8(sl->master, W1_CMD_READ_DATA);
+		w1_write_8(sl->master, reg & 0x00FF);
+		w1_write_8(sl->master, reg>>8 & 0x00FF);
+		*val = w1_read_8(sl->master);
+		*val |= w1_read_8(sl->master)<<8;
+	} else {
+		ret = -ENODEV;
+	}
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return ret;
+}
+
+static int w1_reg_a16_v16_write(void *context, unsigned int reg,
+				unsigned int val)
+{
+	struct device *dev = context;
+	struct w1_slave *sl = container_of(dev, struct w1_slave, dev);
+	int ret = 0;
+
+	if (reg > 65535)
+		return -EINVAL;
+
+	mutex_lock(&sl->master->bus_mutex);
+	if (!w1_reset_select_slave(sl)) {
+		w1_write_8(sl->master, W1_CMD_WRITE_DATA);
+		w1_write_8(sl->master, reg & 0x00FF);
+		w1_write_8(sl->master, reg>>8 & 0x00FF);
+		w1_write_8(sl->master, val & 0x00FF);
+		w1_write_8(sl->master, val>>8 & 0x00FF);
+	} else {
+		ret = -ENODEV;
+	}
+	mutex_unlock(&sl->master->bus_mutex);
+
+	return ret;
+}
+
+/*
+ * Various types of supported bus addressing
+ */
+
+static const struct regmap_bus regmap_w1_bus_a8_v8 = {
+	.reg_read = w1_reg_a8_v8_read,
+	.reg_write = w1_reg_a8_v8_write,
+};
+
+static const struct regmap_bus regmap_w1_bus_a8_v16 = {
+	.reg_read = w1_reg_a8_v16_read,
+	.reg_write = w1_reg_a8_v16_write,
+};
+
+static const struct regmap_bus regmap_w1_bus_a16_v16 = {
+	.reg_read = w1_reg_a16_v16_read,
+	.reg_write = w1_reg_a16_v16_write,
+};
+
+static const struct regmap_bus *regmap_get_w1_bus(struct device *w1_dev,
+					const struct regmap_config *config)
+{
+	if (config->reg_bits == 8 && config->val_bits == 8)
+		return &regmap_w1_bus_a8_v8;
+
+	if (config->reg_bits == 8 && config->val_bits == 16)
+		return &regmap_w1_bus_a8_v16;
+
+	if (config->reg_bits == 16 && config->val_bits == 16)
+		return &regmap_w1_bus_a16_v16;
+
+	return ERR_PTR(-ENOTSUPP);
+}
+
+struct regmap *__regmap_init_w1(struct device *w1_dev,
+				 const struct regmap_config *config,
+				 struct lock_class_key *lock_key,
+				 const char *lock_name)
+{
+
+	const struct regmap_bus *bus = regmap_get_w1_bus(w1_dev, config);
+
+	if (IS_ERR(bus))
+		return ERR_CAST(bus);
+
+	return __regmap_init(w1_dev, bus, w1_dev, config,
+			 lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__regmap_init_w1);
+
+struct regmap *__devm_regmap_init_w1(struct device *w1_dev,
+				 const struct regmap_config *config,
+				 struct lock_class_key *lock_key,
+				 const char *lock_name)
+{
+
+	const struct regmap_bus *bus = regmap_get_w1_bus(w1_dev, config);
+
+	if (IS_ERR(bus))
+		return ERR_CAST(bus);
+
+	return __devm_regmap_init(w1_dev, bus, w1_dev, config,
+				 lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__devm_regmap_init_w1);
+
+MODULE_DESCRIPTION("Register map access API - W1 (1-Wire) support");
+MODULE_LICENSE("GPL");