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, 85 insertions, 0 deletions

diff --git a/drivers/clk/sprd/div.h b/drivers/clk/sprd/div.h
new file mode 100644
index 000000000..a0bcad804
--- /dev/null
+++ b/drivers/clk/sprd/div.h
@@ -0,0 +1,85 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+//
+// Spreadtrum divider clock driver
+//
+// Copyright (C) 2017 Spreadtrum, Inc.
+// Author: Chunyan Zhang <chunyan.zhang@spreadtrum.com>
+
+#ifndef _SPRD_DIV_H_
+#define _SPRD_DIV_H_
+
+#include "common.h"
+
+/**
+ * struct sprd_div_internal - Internal divider description
+ * @shift: Bit offset of the divider in its register
+ * @width: Width of the divider field in its register
+ *
+ * That structure represents a single divider, and is meant to be
+ * embedded in other structures representing the various clock
+ * classes.
+ */
+struct sprd_div_internal {
+	s32	offset;
+	u8	shift;
+	u8	width;
+};
+
+#define _SPRD_DIV_CLK(_offset, _shift, _width)	\
+	{				\
+		.offset = _offset,	\
+		.shift	= _shift,	\
+		.width	= _width,	\
+	}
+
+struct sprd_div {
+	struct sprd_div_internal	div;
+	struct sprd_clk_common	common;
+};
+
+#define SPRD_DIV_CLK_HW_INIT_FN(_struct, _name, _parent, _reg, _offset,	\
+				_shift, _width, _flags, _fn)		\
+	struct sprd_div _struct = {					\
+		.div	= _SPRD_DIV_CLK(_offset, _shift, _width),	\
+		.common	= {						\
+			.regmap		= NULL,				\
+			.reg		= _reg,				\
+			.hw.init	= _fn(_name, _parent,		\
+					      &sprd_div_ops, _flags),	\
+		}							\
+	}
+
+#define SPRD_DIV_CLK(_struct, _name, _parent, _reg,			\
+		     _shift, _width, _flags)				\
+	SPRD_DIV_CLK_HW_INIT_FN(_struct, _name, _parent, _reg, 0x0,	\
+				_shift, _width, _flags, CLK_HW_INIT)
+
+#define SPRD_DIV_CLK_FW_NAME(_struct, _name, _parent, _reg,		\
+			_shift, _width, _flags)				\
+	SPRD_DIV_CLK_HW_INIT_FN(_struct, _name, _parent, _reg, 0x0,	\
+				_shift, _width, _flags, CLK_HW_INIT_FW_NAME)
+
+#define SPRD_DIV_CLK_HW(_struct, _name, _parent, _reg,			\
+			_shift, _width, _flags)				\
+	SPRD_DIV_CLK_HW_INIT_FN(_struct, _name, _parent, _reg, 0x0,	\
+				_shift, _width, _flags, CLK_HW_INIT_HW)
+
+static inline struct sprd_div *hw_to_sprd_div(const struct clk_hw *hw)
+{
+	struct sprd_clk_common *common = hw_to_sprd_clk_common(hw);
+
+	return container_of(common, struct sprd_div, common);
+}
+
+unsigned long sprd_div_helper_recalc_rate(struct sprd_clk_common *common,
+					  const struct sprd_div_internal *div,
+					  unsigned long parent_rate);
+
+int sprd_div_helper_set_rate(const struct sprd_clk_common *common,
+			     const struct sprd_div_internal *div,
+			     unsigned long rate,
+			     unsigned long parent_rate);
+
+extern const struct clk_ops sprd_div_ops;
+
+#endif /* _SPRD_DIV_H_ */