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, 73 insertions, 0 deletions

diff --git a/net/nfc/nci/lib.c b/net/nfc/nci/lib.c
new file mode 100644
index 000000000..473323f80
--- /dev/null
+++ b/net/nfc/nci/lib.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  The NFC Controller Interface is the communication protocol between an
+ *  NFC Controller (NFCC) and a Device Host (DH).
+ *
+ *  Copyright (C) 2011 Texas Instruments, Inc.
+ *
+ *  Written by Ilan Elias <ilane@ti.com>
+ *
+ *  Acknowledgements:
+ *  This file is based on lib.c, which was written
+ *  by Maxim Krasnyansky.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/errno.h>
+
+#include <net/nfc/nci.h>
+#include <net/nfc/nci_core.h>
+
+/* NCI status codes to Unix errno mapping */
+int nci_to_errno(__u8 code)
+{
+	switch (code) {
+	case NCI_STATUS_OK:
+		return 0;
+
+	case NCI_STATUS_REJECTED:
+		return -EBUSY;
+
+	case NCI_STATUS_RF_FRAME_CORRUPTED:
+		return -EBADMSG;
+
+	case NCI_STATUS_NOT_INITIALIZED:
+		return -EHOSTDOWN;
+
+	case NCI_STATUS_SYNTAX_ERROR:
+	case NCI_STATUS_SEMANTIC_ERROR:
+	case NCI_STATUS_INVALID_PARAM:
+	case NCI_STATUS_RF_PROTOCOL_ERROR:
+	case NCI_STATUS_NFCEE_PROTOCOL_ERROR:
+		return -EPROTO;
+
+	case NCI_STATUS_UNKNOWN_GID:
+	case NCI_STATUS_UNKNOWN_OID:
+		return -EBADRQC;
+
+	case NCI_STATUS_MESSAGE_SIZE_EXCEEDED:
+		return -EMSGSIZE;
+
+	case NCI_STATUS_DISCOVERY_ALREADY_STARTED:
+		return -EALREADY;
+
+	case NCI_STATUS_DISCOVERY_TARGET_ACTIVATION_FAILED:
+	case NCI_STATUS_NFCEE_INTERFACE_ACTIVATION_FAILED:
+		return -ECONNREFUSED;
+
+	case NCI_STATUS_RF_TRANSMISSION_ERROR:
+	case NCI_STATUS_NFCEE_TRANSMISSION_ERROR:
+		return -ECOMM;
+
+	case NCI_STATUS_RF_TIMEOUT_ERROR:
+	case NCI_STATUS_NFCEE_TIMEOUT_ERROR:
+		return -ETIMEDOUT;
+
+	case NCI_STATUS_FAILED:
+	default:
+		return -ENOSYS;
+	}
+}
+EXPORT_SYMBOL(nci_to_errno);