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, 54 insertions, 0 deletions

diff --git a/drivers/mfd/madera.h b/drivers/mfd/madera.h
new file mode 100644
index 000000000..900205678
--- /dev/null
+++ b/drivers/mfd/madera.h
@@ -0,0 +1,54 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * MFD internals for Cirrus Logic Madera codecs
+ *
+ * Copyright 2015-2018 Cirrus Logic
+ */
+
+#ifndef MADERA_MFD_H
+#define MADERA_MFD_H
+
+#include <linux/of.h>
+#include <linux/pm.h>
+
+struct madera;
+
+extern const struct dev_pm_ops madera_pm_ops;
+extern const struct of_device_id madera_of_match[];
+
+int madera_dev_init(struct madera *madera);
+int madera_dev_exit(struct madera *madera);
+
+const char *madera_name_from_type(enum madera_type type);
+
+extern const struct regmap_config cs47l15_16bit_spi_regmap;
+extern const struct regmap_config cs47l15_32bit_spi_regmap;
+extern const struct regmap_config cs47l15_16bit_i2c_regmap;
+extern const struct regmap_config cs47l15_32bit_i2c_regmap;
+int cs47l15_patch(struct madera *madera);
+
+extern const struct regmap_config cs47l35_16bit_spi_regmap;
+extern const struct regmap_config cs47l35_32bit_spi_regmap;
+extern const struct regmap_config cs47l35_16bit_i2c_regmap;
+extern const struct regmap_config cs47l35_32bit_i2c_regmap;
+int cs47l35_patch(struct madera *madera);
+
+extern const struct regmap_config cs47l85_16bit_spi_regmap;
+extern const struct regmap_config cs47l85_32bit_spi_regmap;
+extern const struct regmap_config cs47l85_16bit_i2c_regmap;
+extern const struct regmap_config cs47l85_32bit_i2c_regmap;
+int cs47l85_patch(struct madera *madera);
+
+extern const struct regmap_config cs47l90_16bit_spi_regmap;
+extern const struct regmap_config cs47l90_32bit_spi_regmap;
+extern const struct regmap_config cs47l90_16bit_i2c_regmap;
+extern const struct regmap_config cs47l90_32bit_i2c_regmap;
+int cs47l90_patch(struct madera *madera);
+
+extern const struct regmap_config cs47l92_16bit_spi_regmap;
+extern const struct regmap_config cs47l92_32bit_spi_regmap;
+extern const struct regmap_config cs47l92_16bit_i2c_regmap;
+extern const struct regmap_config cs47l92_32bit_i2c_regmap;
+int cs47l92_patch(struct madera *madera);
+
+#endif