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, 41 insertions, 0 deletions

diff --git a/include/media/videobuf2-memops.h b/include/media/videobuf2-memops.h
new file mode 100644
index 000000000..4b5b84f93
--- /dev/null
+++ b/include/media/videobuf2-memops.h
@@ -0,0 +1,41 @@
+/*
+ * videobuf2-memops.h - generic memory handling routines for videobuf2
+ *
+ * Copyright (C) 2010 Samsung Electronics
+ *
+ * Author: Pawel Osciak <pawel@osciak.com>
+ *	   Marek Szyprowski <m.szyprowski@samsung.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation.
+ */
+
+#ifndef _MEDIA_VIDEOBUF2_MEMOPS_H
+#define _MEDIA_VIDEOBUF2_MEMOPS_H
+
+#include <media/videobuf2-v4l2.h>
+#include <linux/mm.h>
+#include <linux/refcount.h>
+
+/**
+ * struct vb2_vmarea_handler - common vma refcount tracking handler.
+ *
+ * @refcount:	pointer to &refcount_t entry in the buffer.
+ * @put:	callback to function that decreases buffer refcount.
+ * @arg:	argument for @put callback.
+ */
+struct vb2_vmarea_handler {
+	refcount_t		*refcount;
+	void			(*put)(void *arg);
+	void			*arg;
+};
+
+extern const struct vm_operations_struct vb2_common_vm_ops;
+
+struct frame_vector *vb2_create_framevec(unsigned long start,
+					 unsigned long length,
+					 bool write);
+void vb2_destroy_framevec(struct frame_vector *vec);
+
+#endif