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, 30 insertions, 0 deletions

diff --git a/net/rds/info.h b/net/rds/info.h
new file mode 100644
index 000000000..1aab62ab6
--- /dev/null
+++ b/net/rds/info.h
@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _RDS_INFO_H
+#define _RDS_INFO_H
+
+struct rds_info_lengths {
+	unsigned int	nr;
+	unsigned int	each;
+};
+
+struct rds_info_iterator;
+
+/*
+ * These functions must fill in the fields of @lens to reflect the size
+ * of the available info source.  If the snapshot fits in @len then it
+ * should be copied using @iter.  The caller will deduce if it was copied
+ * or not by comparing the lengths.
+ */
+typedef void (*rds_info_func)(struct socket *sock, unsigned int len,
+			      struct rds_info_iterator *iter,
+			      struct rds_info_lengths *lens);
+
+void rds_info_register_func(int optname, rds_info_func func);
+void rds_info_deregister_func(int optname, rds_info_func func);
+int rds_info_getsockopt(struct socket *sock, int optname, sockopt_t *opt);
+void rds_info_copy(struct rds_info_iterator *iter, void *data,
+		   unsigned long bytes);
+void rds_info_iter_unmap(struct rds_info_iterator *iter);
+
+
+#endif