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, 168 insertions, 0 deletions

diff --git a/drivers/clk/sprd/gate.h b/drivers/clk/sprd/gate.h
new file mode 100644
index 000000000..775519eb1
--- /dev/null
+++ b/drivers/clk/sprd/gate.h
@@ -0,0 +1,168 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+//
+// Spreadtrum gate clock driver
+//
+// Copyright (C) 2017 Spreadtrum, Inc.
+// Author: Chunyan Zhang <chunyan.zhang@spreadtrum.com>
+
+#ifndef _SPRD_GATE_H_
+#define _SPRD_GATE_H_
+
+#include "common.h"
+
+struct sprd_gate {
+	u32			enable_mask;
+	u16			flags;
+	u16			sc_offset;
+	u16			udelay;
+
+	struct sprd_clk_common	common;
+};
+
+/*
+ * sprd_gate->flags is used for:
+ * CLK_GATE_SET_TO_DISABLE	BIT(0)
+ * CLK_GATE_HIWORD_MASK		BIT(1)
+ * CLK_GATE_BIG_ENDIAN		BIT(2)
+ * so we define new flags from	BIT(3)
+ */
+#define SPRD_GATE_NON_AON BIT(3) /* not always powered on, check before read */
+
+#define SPRD_SC_GATE_CLK_HW_INIT_FN(_struct, _name, _parent, _reg,	\
+				    _sc_offset, _enable_mask, _flags,	\
+				    _gate_flags, _udelay, _ops, _fn)	\
+	struct sprd_gate _struct = {					\
+		.enable_mask	= _enable_mask,				\
+		.sc_offset	= _sc_offset,				\
+		.flags		= _gate_flags,				\
+		.udelay		= _udelay,				\
+		.common	= {						\
+			.regmap		= NULL,				\
+			.reg		= _reg,				\
+			.hw.init	= _fn(_name, _parent,		\
+					      _ops, _flags),		\
+		}							\
+	}
+
+#define SPRD_SC_GATE_CLK_OPS_UDELAY(_struct, _name, _parent, _reg,	\
+				    _sc_offset, _enable_mask, _flags,	\
+				    _gate_flags, _udelay, _ops)		\
+	SPRD_SC_GATE_CLK_HW_INIT_FN(_struct, _name, _parent, _reg,	\
+				    _sc_offset, _enable_mask, _flags,	\
+				    _gate_flags, _udelay, _ops, CLK_HW_INIT)
+
+#define SPRD_SC_GATE_CLK_OPS(_struct, _name, _parent, _reg, _sc_offset,	\
+			     _enable_mask, _flags, _gate_flags, _ops)	\
+	SPRD_SC_GATE_CLK_OPS_UDELAY(_struct, _name, _parent, _reg,	\
+				    _sc_offset, _enable_mask, _flags,	\
+				    _gate_flags, 0, _ops)
+
+#define SPRD_SC_GATE_CLK(_struct, _name, _parent, _reg, _sc_offset,	\
+			 _enable_mask, _flags, _gate_flags)		\
+	SPRD_SC_GATE_CLK_OPS(_struct, _name, _parent, _reg, _sc_offset,	\
+			     _enable_mask, _flags, _gate_flags,		\
+			     &sprd_sc_gate_ops)
+
+#define SPRD_GATE_CLK(_struct, _name, _parent, _reg,			\
+		      _enable_mask, _flags, _gate_flags)		\
+	SPRD_SC_GATE_CLK_OPS(_struct, _name, _parent, _reg, 0,		\
+			     _enable_mask, _flags, _gate_flags,		\
+			     &sprd_gate_ops)
+
+#define SPRD_PLL_SC_GATE_CLK(_struct, _name, _parent, _reg, _sc_offset,	\
+			     _enable_mask, _flags, _gate_flags,		\
+			     _udelay)					\
+	SPRD_SC_GATE_CLK_OPS_UDELAY(_struct, _name, _parent, _reg,	\
+				    _sc_offset,	_enable_mask, _flags,	\
+				    _gate_flags, _udelay,		\
+				    &sprd_pll_sc_gate_ops)
+
+
+#define SPRD_SC_GATE_CLK_HW_OPS_UDELAY(_struct, _name, _parent, _reg,	\
+				       _sc_offset, _enable_mask,	\
+				       _flags, _gate_flags,		\
+				       _udelay, _ops)			\
+	SPRD_SC_GATE_CLK_HW_INIT_FN(_struct, _name, _parent, _reg,	\
+				    _sc_offset, _enable_mask, _flags,	\
+				    _gate_flags, _udelay, _ops,		\
+				    CLK_HW_INIT_HW)
+
+#define SPRD_SC_GATE_CLK_HW_OPS(_struct, _name, _parent, _reg,		\
+				_sc_offset, _enable_mask, _flags,	\
+				_gate_flags, _ops)			\
+	SPRD_SC_GATE_CLK_HW_OPS_UDELAY(_struct, _name, _parent, _reg,	\
+				       _sc_offset, _enable_mask,	\
+				       _flags, _gate_flags, 0, _ops)
+
+#define SPRD_SC_GATE_CLK_HW(_struct, _name, _parent, _reg,		\
+			    _sc_offset, _enable_mask, _flags,		\
+			    _gate_flags)				\
+	SPRD_SC_GATE_CLK_HW_OPS(_struct, _name, _parent, _reg,		\
+				_sc_offset, _enable_mask, _flags,	\
+				_gate_flags, &sprd_sc_gate_ops)
+
+#define SPRD_GATE_CLK_HW(_struct, _name, _parent, _reg,			\
+			 _enable_mask, _flags, _gate_flags)		\
+	SPRD_SC_GATE_CLK_HW_OPS(_struct, _name, _parent, _reg, 0,	\
+				_enable_mask, _flags, _gate_flags,	\
+				&sprd_gate_ops)
+
+#define SPRD_PLL_SC_GATE_CLK_HW(_struct, _name, _parent, _reg,		\
+				_sc_offset, _enable_mask, _flags,	\
+				_gate_flags, _udelay)			\
+	SPRD_SC_GATE_CLK_HW_OPS_UDELAY(_struct, _name, _parent, _reg,	\
+				       _sc_offset, _enable_mask,	\
+				       _flags, _gate_flags, _udelay,	\
+				       &sprd_pll_sc_gate_ops)
+
+#define SPRD_SC_GATE_CLK_FW_NAME_OPS_UDELAY(_struct, _name, _parent,	\
+					    _reg, _sc_offset,		\
+					    _enable_mask, _flags,	\
+					    _gate_flags, _udelay, _ops)	\
+	SPRD_SC_GATE_CLK_HW_INIT_FN(_struct, _name, _parent, _reg,	\
+				    _sc_offset, _enable_mask, _flags,	\
+				    _gate_flags, _udelay, _ops,		\
+				    CLK_HW_INIT_FW_NAME)
+
+#define SPRD_SC_GATE_CLK_FW_NAME_OPS(_struct, _name, _parent, _reg,	\
+				     _sc_offset, _enable_mask, _flags,	\
+				     _gate_flags, _ops)			\
+	SPRD_SC_GATE_CLK_FW_NAME_OPS_UDELAY(_struct, _name, _parent,	\
+					    _reg, _sc_offset,		\
+					    _enable_mask, _flags,	\
+					    _gate_flags, 0, _ops)
+
+#define SPRD_SC_GATE_CLK_FW_NAME(_struct, _name, _parent, _reg,		\
+				 _sc_offset, _enable_mask, _flags,	\
+				 _gate_flags)				\
+	SPRD_SC_GATE_CLK_FW_NAME_OPS(_struct, _name, _parent, _reg,	\
+				     _sc_offset, _enable_mask, _flags,	\
+				     _gate_flags, &sprd_sc_gate_ops)
+
+#define SPRD_GATE_CLK_FW_NAME(_struct, _name, _parent, _reg,		\
+			      _enable_mask, _flags, _gate_flags)	\
+	SPRD_SC_GATE_CLK_FW_NAME_OPS(_struct, _name, _parent, _reg, 0,	\
+				     _enable_mask, _flags, _gate_flags,	\
+				     &sprd_gate_ops)
+
+#define SPRD_PLL_SC_GATE_CLK_FW_NAME(_struct, _name, _parent, _reg,	\
+				     _sc_offset, _enable_mask, _flags,	\
+				     _gate_flags, _udelay)		\
+	SPRD_SC_GATE_CLK_FW_NAME_OPS_UDELAY(_struct, _name, _parent,	\
+					    _reg, _sc_offset,		\
+					    _enable_mask, _flags,	\
+					    _gate_flags, _udelay,	\
+					    &sprd_pll_sc_gate_ops)
+
+static inline struct sprd_gate *hw_to_sprd_gate(const struct clk_hw *hw)
+{
+	struct sprd_clk_common *common = hw_to_sprd_clk_common(hw);
+
+	return container_of(common, struct sprd_gate, common);
+}
+
+extern const struct clk_ops sprd_gate_ops;
+extern const struct clk_ops sprd_sc_gate_ops;
+extern const struct clk_ops sprd_pll_sc_gate_ops;
+
+#endif /* _SPRD_GATE_H_ */