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, 69 insertions, 0 deletions

diff --git a/tools/perf/util/srcline.h b/tools/perf/util/srcline.h
new file mode 100644
index 000000000..1018cbc88
--- /dev/null
+++ b/tools/perf/util/srcline.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef PERF_SRCLINE_H
+#define PERF_SRCLINE_H
+
+#include <linux/list.h>
+#include <linux/rbtree.h>
+#include <linux/types.h>
+
+struct dso;
+struct symbol;
+
+extern bool srcline_full_filename;
+char *get_srcline(struct dso *dso, u64 addr, struct symbol *sym,
+		  bool show_sym, bool show_addr, u64 ip);
+char *__get_srcline(struct dso *dso, u64 addr, struct symbol *sym,
+		  bool show_sym, bool show_addr, bool unwind_inlines,
+		  u64 ip);
+void zfree_srcline(char **srcline);
+char *get_srcline_split(struct dso *dso, u64 addr, unsigned *line);
+
+/* insert the srcline into the DSO, which will take ownership */
+void srcline__tree_insert(struct rb_root_cached *tree, u64 addr, char *srcline);
+/* find previously inserted srcline */
+char *srcline__tree_find(struct rb_root_cached *tree, u64 addr);
+/* delete all srclines within the tree */
+void srcline__tree_delete(struct rb_root_cached *tree);
+
+extern char *srcline__unknown;
+#define SRCLINE_UNKNOWN srcline__unknown
+
+#define MAX_INLINE_NEST 1024
+
+struct inline_list {
+	struct symbol		*symbol;
+	char			*srcline;
+	struct list_head	list;
+};
+
+struct inline_node {
+	u64			addr;
+	struct list_head	val;
+	struct rb_node		rb_node;
+};
+
+/* parse inlined frames for the given address */
+struct inline_node *dso__parse_addr_inlines(struct dso *dso, u64 addr,
+					    struct symbol *sym);
+/* free resources associated to the inline node list */
+void inline_node__delete(struct inline_node *node);
+void inline_node__clear_frames(struct inline_node *node);
+
+/* insert the inline node list into the DSO, which will take ownership */
+void inlines__tree_insert(struct rb_root_cached *tree,
+			  struct inline_node *inlines);
+/* find previously inserted inline node list */
+struct inline_node *inlines__tree_find(struct rb_root_cached *tree, u64 addr);
+/* delete all nodes within the tree of inline_node s */
+void inlines__tree_delete(struct rb_root_cached *tree);
+
+int inline_list__append(struct symbol *symbol, char *srcline, struct inline_node *node);
+int inline_list__append_tail(struct symbol *symbol, char *srcline, struct inline_node *node);
+char *srcline_from_fileline(const char *file, unsigned int line);
+struct symbol *new_inline_sym(struct dso *dso,
+			      struct symbol *base_sym,
+			      const char *funcname);
+
+int addr2line_configure(const char *var, const char *value, void *cb);
+
+#endif /* PERF_SRCLINE_H */