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, 170 insertions, 0 deletions

diff --git a/tools/perf/util/disasm.h b/tools/perf/util/disasm.h
new file mode 100644
index 000000000..25756e3f4
--- /dev/null
+++ b/tools/perf/util/disasm.h
@@ -0,0 +1,170 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef __PERF_UTIL_DISASM_H
+#define __PERF_UTIL_DISASM_H
+
+#include "map_symbol.h"
+
+#ifdef HAVE_LIBDW_SUPPORT
+#include "dwarf-aux.h"
+#endif
+
+struct annotation_options;
+struct disasm_line;
+struct ins;
+struct evsel;
+struct symbol;
+struct data_loc_info;
+struct type_state;
+struct disasm_line;
+
+struct e_machine_and_e_flags {
+	uint32_t e_flags;
+	uint16_t e_machine;
+};
+
+struct arch {
+	/** @name: name such as "x86" or "powerpc". */
+	const char		*name;
+	const struct ins	*instructions;
+	size_t			nr_instructions;
+	size_t			nr_instructions_allocated;
+	const char		*insn_suffix;
+	unsigned int		model;
+	unsigned int		family;
+	/** @id: ELF machine and flags associated with arch. */
+	struct e_machine_and_e_flags id;
+	bool			sorted_instructions;
+	struct		{
+		char comment_char;
+		char skip_functions_char;
+		char register_char;
+		char memory_ref_char;
+		char imm_char;
+	} objdump;
+	bool		(*ins_is_fused)(const struct arch *arch, const char *ins1,
+					const char *ins2);
+	const struct ins_ops  *(*associate_instruction_ops)(struct arch *arch, const char *name);
+#ifdef HAVE_LIBDW_SUPPORT
+	void		(*update_insn_state)(struct type_state *state,
+				struct data_loc_info *dloc, Dwarf_Die *cu_die,
+				struct disasm_line *dl);
+#endif
+};
+
+struct ins {
+	const char     *name;
+	const struct ins_ops *ops;
+};
+
+struct ins_operands {
+	char	*raw;
+	struct {
+		char	*raw;
+		char	*name;
+		struct symbol *sym;
+		u64	addr;
+		s64	offset;
+		bool	offset_avail;
+		bool	outside;
+		bool	multi_regs;
+		bool	mem_ref;
+	} target;
+	union {
+		struct {
+			char	*raw;
+			char	*name;
+			u64	addr;
+			bool	multi_regs;
+			bool	mem_ref;
+		} source;
+		struct {
+			struct ins	    ins;
+			struct ins_operands *ops;
+		} locked;
+		struct {
+			char	*raw_comment;
+			char	*raw_func_start;
+		} jump;
+	};
+};
+
+struct ins_ops {
+	void (*free)(struct ins_operands *ops);
+	int (*parse)(const struct arch *arch, struct ins_operands *ops, struct map_symbol *ms,
+			struct disasm_line *dl);
+	int (*scnprintf)(const struct ins *ins, char *bf, size_t size,
+			 struct ins_operands *ops, int max_ins_name);
+	bool is_jump;
+	bool is_call;
+};
+
+struct annotate_args {
+	const struct arch	  *arch;
+	struct map_symbol	  *ms;
+	struct annotation_options *options;
+	s64			  offset;
+	char			  *line;
+	int			  line_nr;
+	char			  *fileloc;
+};
+
+const struct arch *arch__find(uint16_t e_machine, uint32_t e_flags, const char *cpuid);
+bool arch__is_x86(const struct arch *arch);
+bool arch__is_powerpc(const struct arch *arch);
+
+extern const struct ins_ops call_ops;
+extern const struct ins_ops dec_ops;
+extern const struct ins_ops jump_ops;
+extern const struct ins_ops mov_ops;
+extern const struct ins_ops nop_ops;
+extern const struct ins_ops lock_ops;
+extern const struct ins_ops ret_ops;
+
+int arch__associate_ins_ops(struct arch *arch, const char *name, const struct ins_ops *ops);
+
+const struct arch *arch__new_arc(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_arm(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_arm64(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_csky(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_loongarch(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_mips(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_powerpc(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_riscv64(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_s390(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_sparc(const struct e_machine_and_e_flags *id, const char *cpuid);
+const struct arch *arch__new_x86(const struct e_machine_and_e_flags *id, const char *cpuid);
+
+const struct ins_ops *ins__find(const struct arch *arch, const char *name, struct disasm_line *dl);
+
+bool ins__is_call(const struct ins *ins);
+bool ins__is_jump(const struct ins *ins);
+bool ins__is_fused(const struct arch *arch, const char *ins1, const char *ins2);
+bool ins__is_ret(const struct ins *ins);
+bool ins__is_lock(const struct ins *ins);
+
+const struct ins_ops *check_ppc_insn(struct disasm_line *dl);
+
+struct disasm_line *disasm_line__new(struct annotate_args *args);
+void disasm_line__free(struct disasm_line *dl);
+
+int disasm_line__scnprintf(struct disasm_line *dl, char *bf, size_t size,
+			   bool raw, int max_ins_name);
+
+int ins__raw_scnprintf(const struct ins *ins, char *bf, size_t size,
+			   struct ins_operands *ops, int max_ins_name);
+int ins__scnprintf(const struct ins *ins, char *bf, size_t size,
+		   struct ins_operands *ops, int max_ins_name);
+int call__scnprintf(const struct ins *ins, char *bf, size_t size,
+		    struct ins_operands *ops, int max_ins_name);
+int jump__scnprintf(const struct ins *ins, char *bf, size_t size,
+		    struct ins_operands *ops, int max_ins_name);
+int mov__scnprintf(const struct ins *ins, char *bf, size_t size,
+		   struct ins_operands *ops, int max_ins_name);
+
+void jump__delete(struct ins_operands *ops);
+
+int symbol__disassemble(struct symbol *sym, struct annotate_args *args);
+
+char *expand_tabs(char *line, char **storage, size_t *storage_len);
+
+#endif /* __PERF_UTIL_DISASM_H */