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, 49 insertions, 0 deletions

diff --git a/net/atm/resources.h b/net/atm/resources.h
new file mode 100644
index 000000000..4a0839e92
--- /dev/null
+++ b/net/atm/resources.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* net/atm/resources.h - ATM-related resources */
+
+/* Written 1995-1998 by Werner Almesberger, EPFL LRC/ICA */
+
+
+#ifndef NET_ATM_RESOURCES_H
+#define NET_ATM_RESOURCES_H
+
+#include <linux/atmdev.h>
+#include <linux/mutex.h>
+
+
+extern struct list_head atm_devs;
+extern struct mutex atm_dev_mutex;
+
+int atm_getnames(void __user *buf, int __user *iobuf_len);
+int atm_dev_ioctl(unsigned int cmd, void __user *buf, int __user *sioc_len,
+		  int number, int compat);
+
+#ifdef CONFIG_PROC_FS
+
+#include <linux/proc_fs.h>
+
+void *atm_dev_seq_start(struct seq_file *seq, loff_t *pos);
+void atm_dev_seq_stop(struct seq_file *seq, void *v);
+void *atm_dev_seq_next(struct seq_file *seq, void *v, loff_t *pos);
+
+
+int atm_proc_dev_register(struct atm_dev *dev);
+void atm_proc_dev_deregister(struct atm_dev *dev);
+
+#else
+
+static inline int atm_proc_dev_register(struct atm_dev *dev)
+{
+	return 0;
+}
+
+static inline void atm_proc_dev_deregister(struct atm_dev *dev)
+{
+	/* nothing */
+}
+
+#endif /* CONFIG_PROC_FS */
+
+int atm_register_sysfs(struct atm_dev *adev, struct device *parent);
+void atm_unregister_sysfs(struct atm_dev *adev);
+#endif