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, 52 insertions, 0 deletions

diff --git a/tools/perf/util/dsos.h b/tools/perf/util/dsos.h
new file mode 100644
index 000000000..a26774950
--- /dev/null
+++ b/tools/perf/util/dsos.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __PERF_DSOS
+#define __PERF_DSOS
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <linux/list.h>
+#include <linux/rbtree.h>
+#include "rwsem.h"
+
+struct dso;
+struct dso_id;
+struct kmod_path;
+struct machine;
+
+/*
+ * Collection of DSOs as an array for iteration speed, but sorted for O(n)
+ * lookup.
+ */
+struct dsos {
+	struct rw_semaphore lock;
+	struct dso **dsos;
+	unsigned int cnt;
+	unsigned int allocated;
+	bool sorted;
+};
+
+void dsos__init(struct dsos *dsos);
+void dsos__exit(struct dsos *dsos);
+
+int __dsos__add(struct dsos *dsos, struct dso *dso);
+int dsos__add(struct dsos *dsos, struct dso *dso);
+struct dso *dsos__find(struct dsos *dsos, const char *name, bool cmp_short);
+
+struct dso *dsos__findnew_id(struct dsos *dsos, const char *name, const struct dso_id *id);
+ 
+bool dsos__read_build_ids(struct dsos *dsos, bool with_hits);
+
+size_t dsos__fprintf_buildid(struct dsos *dsos, FILE *fp,
+			       bool (skip)(struct dso *dso, int parm), int parm);
+size_t dsos__fprintf(struct dsos *dsos, FILE *fp);
+
+int dsos__hit_all(struct dsos *dsos);
+
+struct dso *dsos__findnew_module_dso(struct dsos *dsos, struct machine *machine,
+				     struct kmod_path *m, const char *filename);
+
+struct dso *dsos__find_kernel_dso(struct dsos *dsos);
+
+int dsos__for_each_dso(struct dsos *dsos, int (*cb)(struct dso *dso, void *data), void *data);
+
+#endif /* __PERF_DSOS */