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/net/rxrpc/call_state.c b/net/rxrpc/call_state.c
new file mode 100644
index 000000000..6afb54373
--- /dev/null
+++ b/net/rxrpc/call_state.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Call state changing functions.
+ *
+ * Copyright (C) 2022 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include "ar-internal.h"
+
+/*
+ * Transition a call to the complete state.
+ */
+bool rxrpc_set_call_completion(struct rxrpc_call *call,
+				 enum rxrpc_call_completion compl,
+				 u32 abort_code,
+				 int error)
+{
+	if (__rxrpc_call_state(call) == RXRPC_CALL_COMPLETE)
+		return false;
+
+	call->abort_code = abort_code;
+	call->error = error;
+	call->completion = compl;
+	/* Allow reader of completion state to operate locklessly */
+	rxrpc_set_call_state(call, RXRPC_CALL_COMPLETE);
+	trace_rxrpc_call_complete(call);
+	wake_up(&call->waitq);
+	rxrpc_notify_socket(call);
+	return true;
+}
+
+/*
+ * Record that a call successfully completed.
+ */
+bool rxrpc_call_completed(struct rxrpc_call *call)
+{
+	return rxrpc_set_call_completion(call, RXRPC_CALL_SUCCEEDED, 0, 0);
+}
+
+/*
+ * Record that a call is locally aborted.
+ */
+bool rxrpc_abort_call(struct rxrpc_call *call, rxrpc_seq_t seq,
+		      u32 abort_code, int error, enum rxrpc_abort_reason why)
+{
+	trace_rxrpc_abort(call->debug_id, why, call->cid, call->call_id, seq,
+			  abort_code, error);
+	if (!rxrpc_set_call_completion(call, RXRPC_CALL_LOCALLY_ABORTED,
+				       abort_code, error))
+		return false;
+	if (test_bit(RXRPC_CALL_EXPOSED, &call->flags))
+		rxrpc_send_abort_packet(call);
+	return true;
+}
+
+/*
+ * Record that a call errored out before even getting off the ground, thereby
+ * setting the state to allow it to be destroyed.
+ */
+void rxrpc_prefail_call(struct rxrpc_call *call, enum rxrpc_call_completion compl,
+			int error)
+{
+	call->abort_code	= RX_CALL_DEAD;
+	call->error		= error;
+	call->completion	= compl;
+	call->_state		= RXRPC_CALL_COMPLETE;
+	trace_rxrpc_call_complete(call);
+	WARN_ON_ONCE(__test_and_set_bit(RXRPC_CALL_RELEASED, &call->flags));
+}