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, 77 insertions, 0 deletions

diff --git a/net/sunrpc/Kconfig b/net/sunrpc/Kconfig
new file mode 100644
index 000000000..e7808e571
--- /dev/null
+++ b/net/sunrpc/Kconfig
@@ -0,0 +1,77 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config SUNRPC
+	tristate
+	depends on MULTIUSER
+
+config SUNRPC_GSS
+	tristate
+	select OID_REGISTRY
+	depends on MULTIUSER
+
+config SUNRPC_BACKCHANNEL
+	bool
+	depends on SUNRPC
+
+config SUNRPC_SWAP
+	bool
+	depends on SUNRPC
+
+config RPCSEC_GSS_KRB5
+	tristate "Secure RPC: Kerberos V mechanism"
+	depends on SUNRPC && CRYPTO
+	default y
+	select SUNRPC_GSS
+	select CRYPTO_KRB5
+	help
+	  Choose Y here to enable Secure RPC using the Kerberos version 5
+	  GSS-API mechanism (RFC 1964).
+
+	  Secure RPC calls with Kerberos require an auxiliary user-space
+	  daemon which may be found in the Linux nfs-utils package
+	  available from http://linux-nfs.org/.  In addition, user-space
+	  Kerberos support should be installed.
+
+	  If unsure, say Y.
+
+config SUNRPC_DEBUG
+	bool "RPC: Enable dprintk debugging"
+	depends on SUNRPC && SYSCTL
+	select DEBUG_FS
+	help
+	  This option enables a sysctl-based debugging interface
+	  that is be used by the 'rpcdebug' utility to turn on or off
+	  logging of different aspects of the kernel RPC activity.
+
+	  Disabling this option will make your kernel slightly smaller,
+	  but makes troubleshooting NFS issues significantly harder.
+
+	  If unsure, say Y.
+
+config SUNRPC_DEBUG_TRACE
+	bool "RPC: Send dfprintk() output to the trace buffer"
+	depends on SUNRPC_DEBUG && TRACING
+	default n
+	help
+          dprintk() output can be voluminous, which can overwhelm the
+          kernel's logging facility as it must be sent to the console.
+          This option causes dprintk() output to go to the trace buffer
+          instead of the kernel log.
+
+          This will cause warnings about trace_printk() being used to be
+          logged at boot time, so say N unless you are debugging a problem
+          with sunrpc-based clients or services.
+
+config SUNRPC_XPRT_RDMA
+	tristate "RPC-over-RDMA transport"
+	depends on SUNRPC && INFINIBAND && INFINIBAND_ADDR_TRANS
+	default SUNRPC && INFINIBAND
+	select SG_POOL
+	help
+	  This option allows the NFS client and server to use RDMA
+	  transports (InfiniBand, iWARP, or RoCE).
+
+	  To compile this support as a module, choose M. The module
+	  will be called rpcrdma.ko.
+
+	  If unsure, or you know there is no RDMA capability on your
+	  hardware platform, say N.