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, 226 insertions, 0 deletions

diff --git a/drivers/base/regmap/regmap-spmi.c b/drivers/base/regmap/regmap-spmi.c
new file mode 100644
index 000000000..347bfe954
--- /dev/null
+++ b/drivers/base/regmap/regmap-spmi.c
@@ -0,0 +1,226 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Register map access API - SPMI support
+//
+// Copyright (c) 2012-2013, The Linux Foundation. All rights reserved.
+//
+// Based on regmap-i2c.c:
+// Copyright 2011 Wolfson Microelectronics plc
+// Author: Mark Brown <broonie@opensource.wolfsonmicro.com>
+
+#include <linux/regmap.h>
+#include <linux/spmi.h>
+#include <linux/module.h>
+#include <linux/init.h>
+
+static int regmap_spmi_base_read(void *context,
+				 const void *reg, size_t reg_size,
+				 void *val, size_t val_size)
+{
+	u8 addr = *(u8 *)reg;
+	int err = 0;
+
+	BUG_ON(reg_size != 1);
+
+	while (val_size-- && !err)
+		err = spmi_register_read(context, addr++, val++);
+
+	return err;
+}
+
+static int regmap_spmi_base_gather_write(void *context,
+					 const void *reg, size_t reg_size,
+					 const void *val, size_t val_size)
+{
+	const u8 *data = val;
+	u8 addr = *(u8 *)reg;
+	int err = 0;
+
+	BUG_ON(reg_size != 1);
+
+	/*
+	 * SPMI defines a more bandwidth-efficient 'Register 0 Write' sequence,
+	 * use it when possible.
+	 */
+	if (addr == 0 && val_size) {
+		err = spmi_register_zero_write(context, *data);
+		if (err)
+			goto err_out;
+
+		data++;
+		addr++;
+		val_size--;
+	}
+
+	while (val_size) {
+		err = spmi_register_write(context, addr, *data);
+		if (err)
+			goto err_out;
+
+		data++;
+		addr++;
+		val_size--;
+	}
+
+err_out:
+	return err;
+}
+
+static int regmap_spmi_base_write(void *context, const void *data,
+				  size_t count)
+{
+	BUG_ON(count < 1);
+	return regmap_spmi_base_gather_write(context, data, 1, data + 1,
+					     count - 1);
+}
+
+static const struct regmap_bus regmap_spmi_base = {
+	.read				= regmap_spmi_base_read,
+	.write				= regmap_spmi_base_write,
+	.gather_write			= regmap_spmi_base_gather_write,
+	.reg_format_endian_default	= REGMAP_ENDIAN_NATIVE,
+	.val_format_endian_default	= REGMAP_ENDIAN_NATIVE,
+};
+
+struct regmap *__regmap_init_spmi_base(struct spmi_device *sdev,
+				       const struct regmap_config *config,
+				       struct lock_class_key *lock_key,
+				       const char *lock_name)
+{
+	return __regmap_init(&sdev->dev, &regmap_spmi_base, sdev, config,
+			     lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__regmap_init_spmi_base);
+
+struct regmap *__devm_regmap_init_spmi_base(struct spmi_device *sdev,
+					    const struct regmap_config *config,
+					    struct lock_class_key *lock_key,
+					    const char *lock_name)
+{
+	return __devm_regmap_init(&sdev->dev, &regmap_spmi_base, sdev, config,
+				  lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__devm_regmap_init_spmi_base);
+
+static int regmap_spmi_ext_read(void *context,
+				const void *reg, size_t reg_size,
+				void *val, size_t val_size)
+{
+	int err = 0;
+	size_t len;
+	u16 addr;
+
+	BUG_ON(reg_size != 2);
+
+	addr = *(u16 *)reg;
+
+	/*
+	 * Split accesses into two to take advantage of the more
+	 * bandwidth-efficient 'Extended Register Read' command when possible
+	 */
+	while (addr <= 0xFF && val_size) {
+		len = min_t(size_t, val_size, 16);
+
+		err = spmi_ext_register_read(context, addr, val, len);
+		if (err)
+			goto err_out;
+
+		addr += len;
+		val += len;
+		val_size -= len;
+	}
+
+	while (val_size) {
+		len = min_t(size_t, val_size, 8);
+
+		err = spmi_ext_register_readl(context, addr, val, len);
+		if (err)
+			goto err_out;
+
+		addr += len;
+		val += len;
+		val_size -= len;
+	}
+
+err_out:
+	return err;
+}
+
+static int regmap_spmi_ext_gather_write(void *context,
+					const void *reg, size_t reg_size,
+					const void *val, size_t val_size)
+{
+	int err = 0;
+	size_t len;
+	u16 addr;
+
+	BUG_ON(reg_size != 2);
+
+	addr = *(u16 *)reg;
+
+	while (addr <= 0xFF && val_size) {
+		len = min_t(size_t, val_size, 16);
+
+		err = spmi_ext_register_write(context, addr, val, len);
+		if (err)
+			goto err_out;
+
+		addr += len;
+		val += len;
+		val_size -= len;
+	}
+
+	while (val_size) {
+		len = min_t(size_t, val_size, 8);
+
+		err = spmi_ext_register_writel(context, addr, val, len);
+		if (err)
+			goto err_out;
+
+		addr += len;
+		val += len;
+		val_size -= len;
+	}
+
+err_out:
+	return err;
+}
+
+static int regmap_spmi_ext_write(void *context, const void *data,
+				 size_t count)
+{
+	BUG_ON(count < 2);
+	return regmap_spmi_ext_gather_write(context, data, 2, data + 2,
+					    count - 2);
+}
+
+static const struct regmap_bus regmap_spmi_ext = {
+	.read				= regmap_spmi_ext_read,
+	.write				= regmap_spmi_ext_write,
+	.gather_write			= regmap_spmi_ext_gather_write,
+	.reg_format_endian_default	= REGMAP_ENDIAN_NATIVE,
+	.val_format_endian_default	= REGMAP_ENDIAN_NATIVE,
+};
+
+struct regmap *__regmap_init_spmi_ext(struct spmi_device *sdev,
+				      const struct regmap_config *config,
+				      struct lock_class_key *lock_key,
+				      const char *lock_name)
+{
+	return __regmap_init(&sdev->dev, &regmap_spmi_ext, sdev, config,
+			     lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__regmap_init_spmi_ext);
+
+struct regmap *__devm_regmap_init_spmi_ext(struct spmi_device *sdev,
+					   const struct regmap_config *config,
+					   struct lock_class_key *lock_key,
+					   const char *lock_name)
+{
+	return __devm_regmap_init(&sdev->dev, &regmap_spmi_ext, sdev, config,
+				  lock_key, lock_name);
+}
+EXPORT_SYMBOL_GPL(__devm_regmap_init_spmi_ext);
+
+MODULE_DESCRIPTION("Register map access API - SPMI support");
+MODULE_LICENSE("GPL");