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, 66 insertions, 0 deletions

diff --git a/include/uapi/rdma/rvt-abi.h b/include/uapi/rdma/rvt-abi.h
new file mode 100644
index 000000000..7c05a02d2
--- /dev/null
+++ b/include/uapi/rdma/rvt-abi.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause) */
+
+/*
+ * This file contains defines, structures, etc. that are used
+ * to communicate between kernel and user code.
+ */
+
+#ifndef RVT_ABI_USER_H
+#define RVT_ABI_USER_H
+
+#include <linux/types.h>
+#include <rdma/ib_user_verbs.h>
+#ifndef RDMA_ATOMIC_UAPI
+#define RDMA_ATOMIC_UAPI(_type, _name) struct{ _type val; } _name
+#endif
+
+struct rvt_wqe_sge {
+	__aligned_u64 addr;
+	__u32 length;
+	__u32 lkey;
+};
+
+/*
+ * This structure is used to contain the head pointer, tail pointer,
+ * and completion queue entries as a single memory allocation so
+ * it can be mmap'ed into user space.
+ */
+struct rvt_cq_wc {
+	/* index of next entry to fill */
+	RDMA_ATOMIC_UAPI(__u32, head);
+	/* index of next ib_poll_cq() entry */
+	RDMA_ATOMIC_UAPI(__u32, tail);
+
+	/* these are actually size ibcq.cqe + 1 */
+	struct ib_uverbs_wc uqueue[];
+};
+
+/*
+ * Receive work request queue entry.
+ * The size of the sg_list is determined when the QP (or SRQ) is created
+ * and stored in qp->r_rq.max_sge (or srq->rq.max_sge).
+ */
+struct rvt_rwqe {
+	__u64 wr_id;
+	__u8 num_sge;
+	__u8 padding[7];
+	struct rvt_wqe_sge sg_list[];
+};
+
+/*
+ * This structure is used to contain the head pointer, tail pointer,
+ * and receive work queue entries as a single memory allocation so
+ * it can be mmap'ed into user space.
+ * Note that the wq array elements are variable size so you can't
+ * just index into the array to get the N'th element;
+ * use get_rwqe_ptr() for user space and rvt_get_rwqe_ptr()
+ * for kernel space.
+ */
+struct rvt_rwq {
+	/* new work requests posted to the head */
+	RDMA_ATOMIC_UAPI(__u32, head);
+	/* receives pull requests from here. */
+	RDMA_ATOMIC_UAPI(__u32, tail);
+	struct rvt_rwqe wq[];
+};
+#endif /* RVT_ABI_USER_H */