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, 63 insertions, 0 deletions

diff --git a/net/9p/Kconfig b/net/9p/Kconfig
new file mode 100644
index 000000000..22f8c1678
--- /dev/null
+++ b/net/9p/Kconfig
@@ -0,0 +1,63 @@
+# SPDX-License-Identifier: GPL-2.0-only
+#
+# 9P protocol configuration
+#
+
+menuconfig NET_9P
+	tristate "Plan 9 Resource Sharing Support (9P2000)"
+	select NETFS_SUPPORT
+	help
+	  If you say Y here, you will get experimental support for
+	  Plan 9 resource sharing via the 9P2000 protocol.
+
+	  See <http://v9fs.sf.net> for more information.
+
+	  If unsure, say N.
+
+if NET_9P
+
+config NET_9P_FD
+	default NET_9P
+	imply INET
+	imply UNIX
+	tristate "9P FD Transport"
+	help
+	  This builds support for transports over TCP, Unix sockets and
+	  filedescriptors.
+
+config NET_9P_VIRTIO
+	depends on VIRTIO
+	tristate "9P Virtio Transport"
+	help
+	  This builds support for a transports between
+	  guest partitions and a host partition.
+
+config NET_9P_XEN
+	depends on XEN
+	select XEN_XENBUS_FRONTEND
+	tristate "9P Xen Transport"
+	help
+	  This builds support for a transport for 9pfs between
+	  two Xen domains.
+
+config NET_9P_USBG
+	tristate "9P USB Gadget Transport"
+	depends on USB_GADGET
+	select CONFIGFS_FS
+	select USB_LIBCOMPOSITE
+	help
+	  This builds support for a transport for 9pfs over
+	  usb gadget.
+
+config NET_9P_RDMA
+	depends on INET && INFINIBAND && INFINIBAND_ADDR_TRANS
+	tristate "9P RDMA Transport (Experimental)"
+	help
+	  This builds support for an RDMA transport.
+
+config NET_9P_DEBUG
+	bool "Debug information"
+	help
+	  Say Y if you want the 9P subsystem to log debug information.
+
+endif