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, 37 insertions, 0 deletions

diff --git a/include/rdma/ib_sysfs.h b/include/rdma/ib_sysfs.h
new file mode 100644
index 000000000..3b77cfd74
--- /dev/null
+++ b/include/rdma/ib_sysfs.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause */
+/*
+ * Copyright (c) 2021 Mellanox Technologies Ltd.  All rights reserved.
+ */
+#ifndef DEF_RDMA_IB_SYSFS_H
+#define DEF_RDMA_IB_SYSFS_H
+
+#include <linux/sysfs.h>
+
+struct ib_device;
+
+struct ib_port_attribute {
+	struct attribute attr;
+	ssize_t (*show)(struct ib_device *ibdev, u32 port_num,
+			struct ib_port_attribute *attr, char *buf);
+	ssize_t (*store)(struct ib_device *ibdev, u32 port_num,
+			 struct ib_port_attribute *attr, const char *buf,
+			 size_t count);
+};
+
+#define IB_PORT_ATTR_RW(_name)                                                 \
+	struct ib_port_attribute ib_port_attr_##_name = __ATTR_RW(_name)
+
+#define IB_PORT_ATTR_ADMIN_RW(_name)                                           \
+	struct ib_port_attribute ib_port_attr_##_name =                        \
+		__ATTR_RW_MODE(_name, 0600)
+
+#define IB_PORT_ATTR_RO(_name)                                                 \
+	struct ib_port_attribute ib_port_attr_##_name = __ATTR_RO(_name)
+
+#define IB_PORT_ATTR_WO(_name)                                                 \
+	struct ib_port_attribute ib_port_attr_##_name = __ATTR_WO(_name)
+
+struct ib_device *ib_port_sysfs_get_ibdev_kobj(struct kobject *kobj,
+					       u32 *port_num);
+
+#endif