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, 450 insertions, 0 deletions

diff --git a/drivers/base/regmap/regmap-i2c.c b/drivers/base/regmap/regmap-i2c.c
new file mode 100644
index 000000000..51a04961f
--- /dev/null
+++ b/drivers/base/regmap/regmap-i2c.c
@@ -0,0 +1,450 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Register map access API - I2C support
+//
+// Copyright 2011 Wolfson Microelectronics plc
+//
+// Author: Mark Brown <broonie@opensource.wolfsonmicro.com>
+
+#include <linux/regmap.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+
+#include "internal.h"
+
+static int regmap_smbus_byte_reg_read(void *context, unsigned int reg,
+				      unsigned int *val)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	int ret;
+
+	if (reg > 0xff)
+		return -EINVAL;
+
+	ret = i2c_smbus_read_byte_data(i2c, reg);
+	if (ret < 0)
+		return ret;
+
+	*val = ret;
+
+	return 0;
+}
+
+static int regmap_smbus_byte_reg_write(void *context, unsigned int reg,
+				       unsigned int val)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+
+	if (val > 0xff || reg > 0xff)
+		return -EINVAL;
+
+	return i2c_smbus_write_byte_data(i2c, reg, val);
+}
+
+static const struct regmap_bus regmap_smbus_byte = {
+	.reg_write = regmap_smbus_byte_reg_write,
+	.reg_read = regmap_smbus_byte_reg_read,
+};
+
+static int regmap_smbus_word_reg_read(void *context, unsigned int reg,
+				      unsigned int *val)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	int ret;
+
+	if (reg > 0xff)
+		return -EINVAL;
+
+	ret = i2c_smbus_read_word_data(i2c, reg);
+	if (ret < 0)
+		return ret;
+
+	*val = ret;
+
+	return 0;
+}
+
+static int regmap_smbus_word_reg_write(void *context, unsigned int reg,
+				       unsigned int val)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+
+	if (val > 0xffff || reg > 0xff)
+		return -EINVAL;
+
+	return i2c_smbus_write_word_data(i2c, reg, val);
+}
+
+static const struct regmap_bus regmap_smbus_word = {
+	.reg_write = regmap_smbus_word_reg_write,
+	.reg_read = regmap_smbus_word_reg_read,
+};
+
+static int regmap_smbus_word_read_swapped(void *context, unsigned int reg,
+					  unsigned int *val)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	int ret;
+
+	if (reg > 0xff)
+		return -EINVAL;
+
+	ret = i2c_smbus_read_word_swapped(i2c, reg);
+	if (ret < 0)
+		return ret;
+
+	*val = ret;
+
+	return 0;
+}
+
+static int regmap_smbus_word_write_swapped(void *context, unsigned int reg,
+					   unsigned int val)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+
+	if (val > 0xffff || reg > 0xff)
+		return -EINVAL;
+
+	return i2c_smbus_write_word_swapped(i2c, reg, val);
+}
+
+static const struct regmap_bus regmap_smbus_word_swapped = {
+	.reg_write = regmap_smbus_word_write_swapped,
+	.reg_read = regmap_smbus_word_read_swapped,
+};
+
+static int regmap_i2c_write(void *context, const void *data, size_t count)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	int ret;
+
+	ret = i2c_master_send(i2c, data, count);
+	if (ret == count)
+		return 0;
+	else if (ret < 0)
+		return ret;
+	else
+		return -EIO;
+}
+
+static int regmap_i2c_gather_write(void *context,
+				   const void *reg, size_t reg_size,
+				   const void *val, size_t val_size)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	struct i2c_msg xfer[2];
+	int ret;
+
+	/* If the I2C controller can't do a gather tell the core, it
+	 * will substitute in a linear write for us.
+	 */
+	if (!i2c_check_functionality(i2c->adapter, I2C_FUNC_NOSTART))
+		return -ENOTSUPP;
+
+	xfer[0].addr = i2c->addr;
+	xfer[0].flags = 0;
+	xfer[0].len = reg_size;
+	xfer[0].buf = (void *)reg;
+
+	xfer[1].addr = i2c->addr;
+	xfer[1].flags = I2C_M_NOSTART;
+	xfer[1].len = val_size;
+	xfer[1].buf = (void *)val;
+
+	ret = i2c_transfer(i2c->adapter, xfer, 2);
+	if (ret == 2)
+		return 0;
+	if (ret < 0)
+		return ret;
+	else
+		return -EIO;
+}
+
+static int regmap_i2c_read(void *context,
+			   const void *reg, size_t reg_size,
+			   void *val, size_t val_size)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	struct i2c_msg xfer[2];
+	int ret;
+
+	xfer[0].addr = i2c->addr;
+	xfer[0].flags = 0;
+	xfer[0].len = reg_size;
+	xfer[0].buf = (void *)reg;
+
+	xfer[1].addr = i2c->addr;
+	xfer[1].flags = I2C_M_RD;
+	xfer[1].len = val_size;
+	xfer[1].buf = val;
+
+	ret = i2c_transfer(i2c->adapter, xfer, 2);
+	if (ret == 2)
+		return 0;
+	else if (ret < 0)
+		return ret;
+	else
+		return -EIO;
+}
+
+static const struct regmap_bus regmap_i2c = {
+	.write = regmap_i2c_write,
+	.gather_write = regmap_i2c_gather_write,
+	.read = regmap_i2c_read,
+	.reg_format_endian_default = REGMAP_ENDIAN_BIG,
+	.val_format_endian_default = REGMAP_ENDIAN_BIG,
+};
+
+static int regmap_i2c_smbus_i2c_write(void *context, const void *data,
+				      size_t count)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+
+	if (count < 1)
+		return -EINVAL;
+
+	--count;
+	return i2c_smbus_write_i2c_block_data(i2c, ((u8 *)data)[0], count,
+					      ((u8 *)data + 1));
+}
+
+static int regmap_i2c_smbus_i2c_read(void *context, const void *reg,
+				     size_t reg_size, void *val,
+				     size_t val_size)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	int ret;
+
+	if (reg_size != 1 || val_size < 1)
+		return -EINVAL;
+
+	ret = i2c_smbus_read_i2c_block_data(i2c, ((u8 *)reg)[0], val_size, val);
+	if (ret == val_size)
+		return 0;
+	else if (ret < 0)
+		return ret;
+	else
+		return -EIO;
+}
+
+static const struct regmap_bus regmap_i2c_smbus_i2c_block = {
+	.write = regmap_i2c_smbus_i2c_write,
+	.read = regmap_i2c_smbus_i2c_read,
+	.max_raw_read = I2C_SMBUS_BLOCK_MAX - 1,
+	.max_raw_write = I2C_SMBUS_BLOCK_MAX - 1,
+};
+
+static int regmap_i2c_smbus_i2c_write_reg16(void *context, const void *data,
+				      size_t count)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+
+	if (count < 2)
+		return -EINVAL;
+
+	count--;
+	return i2c_smbus_write_i2c_block_data(i2c, ((u8 *)data)[0], count,
+					      (u8 *)data + 1);
+}
+
+static int regmap_i2c_smbus_i2c_read_reg16(void *context, const void *reg,
+				     size_t reg_size, void *val,
+				     size_t val_size)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	int ret, count, len = val_size;
+
+	if (reg_size != 2)
+		return -EINVAL;
+
+	ret = i2c_smbus_write_byte_data(i2c, ((u16 *)reg)[0] & 0xff,
+					((u16 *)reg)[0] >> 8);
+	if (ret < 0)
+		return ret;
+
+	count = 0;
+	do {
+		/* Current Address Read */
+		ret = i2c_smbus_read_byte(i2c);
+		if (ret < 0)
+			break;
+
+		*((u8 *)val++) = ret;
+		count++;
+		len--;
+	} while (len > 0);
+
+	if (count == val_size)
+		return 0;
+	else if (ret < 0)
+		return ret;
+	else
+		return -EIO;
+}
+
+static const struct regmap_bus regmap_i2c_smbus_i2c_block_reg16 = {
+	.write = regmap_i2c_smbus_i2c_write_reg16,
+	.read = regmap_i2c_smbus_i2c_read_reg16,
+	.max_raw_read = I2C_SMBUS_BLOCK_MAX - 2,
+	.max_raw_write = I2C_SMBUS_BLOCK_MAX - 2,
+};
+
+/*
+ * SMBus byte/word reg16 support for adapters that have SMBUS_BYTE_DATA
+ * and SMBUS_WORD_DATA but lack I2C_FUNC_I2C and I2C_FUNC_SMBUS_I2C_BLOCK,
+ * such as the AMD PIIX4.
+ *
+ * READ:  set 16-bit EEPROM address via write_byte_data(addr_lo, addr_hi),
+ *        then sequentially read bytes via read_byte() (EEPROM auto-
+ *        increments the address pointer).  Same as the I2C-block reg16
+ *        read path above.
+ *
+ * WRITE: encode the low address byte and data into a word transaction:
+ *        write_word_data(addr_hi, (data_byte << 8) | addr_lo).
+ *        Only single-byte writes are supported (one value per transaction).
+ */
+static int regmap_smbus_word_write_reg16(void *context, const void *data,
+					 size_t count)
+{
+	struct device *dev = context;
+	struct i2c_client *i2c = to_i2c_client(dev);
+	u8 addr_hi, addr_lo, val;
+
+	/*
+	 * data layout: [addr_hi, addr_lo, val0, val1, ...].
+	 * Only single-byte value writes are supported; multi-byte would
+	 * require raw I2C (or repeated word writes with incrementing address).
+	 */
+	if (count != 3)
+		return -EINVAL;
+
+	addr_hi = ((u8 *)data)[0];
+	addr_lo = ((u8 *)data)[1];
+	val = ((u8 *)data)[2];
+
+	return i2c_smbus_write_word_data(i2c, addr_hi,
+					 ((u16)val << 8) | addr_lo);
+}
+
+static const struct regmap_bus regmap_smbus_byte_word_reg16 = {
+	.write = regmap_smbus_word_write_reg16,
+	.read = regmap_i2c_smbus_i2c_read_reg16,
+	.max_raw_read = I2C_SMBUS_BLOCK_MAX - 2,
+	.max_raw_write = 1,
+};
+
+static const struct regmap_bus *regmap_get_i2c_bus(struct i2c_client *i2c,
+					const struct regmap_config *config)
+{
+	const struct i2c_adapter_quirks *quirks;
+	const struct regmap_bus *bus = NULL;
+	struct regmap_bus *ret_bus;
+	u16 max_read = 0, max_write = 0;
+
+	if (i2c_check_functionality(i2c->adapter, I2C_FUNC_I2C))
+		bus = &regmap_i2c;
+	else if (config->val_bits == 8 && config->reg_bits == 8 &&
+		 i2c_check_functionality(i2c->adapter,
+					 I2C_FUNC_SMBUS_I2C_BLOCK))
+		bus = &regmap_i2c_smbus_i2c_block;
+	else if (config->val_bits == 8 && config->reg_bits == 16 &&
+		i2c_check_functionality(i2c->adapter,
+					I2C_FUNC_SMBUS_I2C_BLOCK))
+		bus = &regmap_i2c_smbus_i2c_block_reg16;
+	else if (config->val_bits == 8 && config->reg_bits == 16 &&
+		 i2c_check_functionality(i2c->adapter,
+					I2C_FUNC_SMBUS_BYTE_DATA |
+					I2C_FUNC_SMBUS_WORD_DATA))
+		bus = &regmap_smbus_byte_word_reg16;
+	else if (config->val_bits == 16 && config->reg_bits == 8 &&
+		 i2c_check_functionality(i2c->adapter,
+					 I2C_FUNC_SMBUS_WORD_DATA))
+		switch (regmap_get_val_endian(&i2c->dev, NULL, config)) {
+		case REGMAP_ENDIAN_LITTLE:
+			bus = &regmap_smbus_word;
+			break;
+		case REGMAP_ENDIAN_BIG:
+			bus = &regmap_smbus_word_swapped;
+			break;
+		default:		/* everything else is not supported */
+			break;
+		}
+	else if (config->val_bits == 8 && config->reg_bits == 8 &&
+		 i2c_check_functionality(i2c->adapter,
+					 I2C_FUNC_SMBUS_BYTE_DATA))
+		bus = &regmap_smbus_byte;
+
+	if (!bus)
+		return ERR_PTR(-ENOTSUPP);
+
+	quirks = i2c->adapter->quirks;
+	if (quirks) {
+		if (quirks->max_read_len &&
+		    (bus->max_raw_read == 0 || bus->max_raw_read > quirks->max_read_len))
+			max_read = quirks->max_read_len;
+
+		if (quirks->max_write_len &&
+		    (bus->max_raw_write == 0 || bus->max_raw_write > quirks->max_write_len))
+			max_write = quirks->max_write_len -
+				(config->reg_bits + config->pad_bits) / BITS_PER_BYTE;
+
+		if (max_read || max_write) {
+			ret_bus = kmemdup(bus, sizeof(*bus), GFP_KERNEL);
+			if (!ret_bus)
+				return ERR_PTR(-ENOMEM);
+			ret_bus->free_on_exit = true;
+			ret_bus->max_raw_read = max_read;
+			ret_bus->max_raw_write = max_write;
+			bus = ret_bus;
+		}
+	}
+
+	return bus;
+}
+
+struct regmap *__regmap_init_i2c(struct i2c_client *i2c,
+				 const struct regmap_config *config,
+				 struct lock_class_key *lock_key,
+				 const char *lock_name)
+{
+	const struct regmap_bus *bus = regmap_get_i2c_bus(i2c, config);
+
+	if (IS_ERR(bus))
+		return ERR_CAST(bus);
+
+	return __regmap_init(&i2c->dev, bus, &i2c->dev, config,
+			     lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__regmap_init_i2c);
+
+struct regmap *__devm_regmap_init_i2c(struct i2c_client *i2c,
+				      const struct regmap_config *config,
+				      struct lock_class_key *lock_key,
+				      const char *lock_name)
+{
+	const struct regmap_bus *bus = regmap_get_i2c_bus(i2c, config);
+
+	if (IS_ERR(bus))
+		return ERR_CAST(bus);
+
+	return __devm_regmap_init(&i2c->dev, bus, &i2c->dev, config,
+				  lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__devm_regmap_init_i2c);
+
+MODULE_DESCRIPTION("Register map access API - I2C support");
+MODULE_LICENSE("GPL");