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, 51 insertions, 0 deletions

diff --git a/net/atm/common.h b/net/atm/common.h
new file mode 100644
index 000000000..11cb51dd7
--- /dev/null
+++ b/net/atm/common.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* net/atm/common.h - ATM sockets (common part for PVC and SVC) */
+
+/* Written 1995-2000 by Werner Almesberger, EPFL LRC/ICA */
+
+
+#ifndef NET_ATM_COMMON_H
+#define NET_ATM_COMMON_H
+
+#include <linux/net.h>
+#include <linux/poll.h> /* for poll_table */
+
+
+int vcc_create(struct net *net, struct socket *sock, int protocol, int family, int kern);
+int vcc_release(struct socket *sock);
+int vcc_connect(struct socket *sock, int itf, short vpi, int vci);
+int vcc_recvmsg(struct socket *sock, struct msghdr *msg, size_t size,
+		int flags);
+int vcc_sendmsg(struct socket *sock, struct msghdr *m, size_t total_len);
+__poll_t vcc_poll(struct file *file, struct socket *sock, poll_table *wait);
+int vcc_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg);
+int vcc_compat_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg);
+int vcc_setsockopt(struct socket *sock, int level, int optname,
+		   sockptr_t optval, unsigned int optlen);
+int vcc_getsockopt(struct socket *sock, int level, int optname,
+		   sockopt_t *opt);
+void vcc_process_recv_queue(struct atm_vcc *vcc);
+
+int atmpvc_init(void);
+void atmpvc_exit(void);
+int atm_sysfs_init(void);
+void atm_sysfs_exit(void);
+
+#ifdef CONFIG_PROC_FS
+int atm_proc_init(void);
+void atm_proc_exit(void);
+#else
+static inline int atm_proc_init(void)
+{
+	return 0;
+}
+
+static inline void atm_proc_exit(void)
+{
+	/* nothing */
+}
+#endif /* CONFIG_PROC_FS */
+
+void atm_dev_release_vccs(struct atm_dev *dev);
+
+#endif