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, 80 insertions, 0 deletions

diff --git a/tools/perf/util/config.h b/tools/perf/util/config.h
new file mode 100644
index 000000000..987b47cf5
--- /dev/null
+++ b/tools/perf/util/config.h
@@ -0,0 +1,80 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_CONFIG_H
+#define __PERF_CONFIG_H
+
+#include <stdbool.h>
+#include <linux/list.h>
+
+struct perf_config_item {
+	char *name;
+	char *value;
+	bool from_system_config;
+	struct list_head node;
+};
+
+struct perf_config_section {
+	char *name;
+	struct list_head items;
+	bool from_system_config;
+	struct list_head node;
+};
+
+struct perf_config_set {
+	struct list_head sections;
+};
+
+extern const char *config_exclusive_filename;
+
+typedef int (*config_fn_t)(const char *, const char *, void *);
+
+int perf_default_config(const char *, const char *, void *);
+int perf_config(config_fn_t fn, void *);
+int perf_config_scan(const char *name, const char *fmt, ...) __scanf(2, 3);
+const char *perf_config_get(const char *name);
+int perf_config_set(struct perf_config_set *set,
+		    config_fn_t fn, void *data);
+int perf_config_int(int *dest, const char *, const char *);
+int perf_config_u8(u8 *dest, const char *name, const char *value);
+int perf_config_u64(u64 *dest, const char *, const char *);
+int perf_config_bool(const char *, const char *);
+int config_error_nonbool(const char *);
+const char *perf_etc_perfconfig(void);
+const char *perf_home_perfconfig(void);
+int perf_config_system(void);
+int perf_config_global(void);
+
+struct perf_config_set *perf_config_set__new(void);
+struct perf_config_set *perf_config_set__load_file(const char *file);
+void perf_config_set__delete(struct perf_config_set *set);
+int perf_config_set__collect(struct perf_config_set *set, const char *file_name,
+			     const char *var, const char *value);
+void perf_config__exit(void);
+int perf_config__set_variable(const char *var, const char *value);
+
+/**
+ * perf_config_sections__for_each - iterate thru all the sections
+ * @list: list_head instance to iterate
+ * @section: struct perf_config_section iterator
+ */
+#define perf_config_sections__for_each_entry(list, section)	\
+        list_for_each_entry(section, list, node)
+
+/**
+ * perf_config_items__for_each - iterate thru all the items
+ * @list: list_head instance to iterate
+ * @item: struct perf_config_item iterator
+ */
+#define perf_config_items__for_each_entry(list, item)	\
+        list_for_each_entry(item, list, node)
+
+/**
+ * perf_config_set__for_each - iterate thru all the config section-item pairs
+ * @set: evlist instance to iterate
+ * @section: struct perf_config_section iterator
+ * @item: struct perf_config_item iterator
+ */
+#define perf_config_set__for_each_entry(set, section, item)			\
+	perf_config_sections__for_each_entry(&set->sections, section)		\
+	perf_config_items__for_each_entry(&section->items, item)
+
+#endif /* __PERF_CONFIG_H */