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, 61 insertions, 0 deletions

diff --git a/include/net/wext.h b/include/net/wext.h
new file mode 100644
index 000000000..aa192a670
--- /dev/null
+++ b/include/net/wext.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __NET_WEXT_H
+#define __NET_WEXT_H
+
+#include <net/iw_handler.h>
+
+struct net;
+
+#ifdef CONFIG_WEXT_CORE
+int wext_handle_ioctl(struct net *net, unsigned int cmd,
+		      void __user *arg);
+int compat_wext_handle_ioctl(struct net *net, unsigned int cmd,
+			     unsigned long arg);
+
+struct iw_statistics *get_wireless_stats(struct net_device *dev);
+int call_commit_handler(struct net_device *dev);
+#else
+static inline int wext_handle_ioctl(struct net *net, unsigned int cmd,
+				    void __user *arg)
+{
+	return -EINVAL;
+}
+static inline int compat_wext_handle_ioctl(struct net *net, unsigned int cmd,
+					   unsigned long arg)
+{
+	return -EINVAL;
+}
+#endif
+
+#ifdef CONFIG_WEXT_PROC
+int wext_proc_init(struct net *net);
+void wext_proc_exit(struct net *net);
+#else
+static inline int wext_proc_init(struct net *net)
+{
+	return 0;
+}
+static inline void wext_proc_exit(struct net *net)
+{
+	return;
+}
+#endif
+
+#ifdef CONFIG_WEXT_PRIV
+int ioctl_private_call(struct net_device *dev, struct iwreq *iwr,
+		       unsigned int cmd, struct iw_request_info *info,
+		       iw_handler handler);
+int compat_private_call(struct net_device *dev, struct iwreq *iwr,
+			unsigned int cmd, struct iw_request_info *info,
+			iw_handler handler);
+int iw_handler_get_private(struct net_device *		dev,
+			   struct iw_request_info *	info,
+			   union iwreq_data *		wrqu,
+			   char *			extra);
+#else
+#define ioctl_private_call NULL
+#define compat_private_call NULL
+#endif
+
+
+#endif /* __NET_WEXT_H */