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, 47 insertions, 0 deletions

diff --git a/fs/nilfs2/dat.h b/fs/nilfs2/dat.h
new file mode 100644
index 000000000..468c82d26
--- /dev/null
+++ b/fs/nilfs2/dat.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * NILFS disk address translation.
+ *
+ * Copyright (C) 2006-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * Written by Koji Sato.
+ */
+
+#ifndef _NILFS_DAT_H
+#define _NILFS_DAT_H
+
+#include <linux/types.h>
+#include <linux/buffer_head.h>
+#include <linux/fs.h>
+#include <linux/nilfs2_ondisk.h>	/* nilfs_inode, nilfs_checkpoint */
+
+
+struct nilfs_palloc_req;
+
+int nilfs_dat_translate(struct inode *, __u64, sector_t *);
+
+int nilfs_dat_prepare_alloc(struct inode *, struct nilfs_palloc_req *);
+void nilfs_dat_commit_alloc(struct inode *, struct nilfs_palloc_req *);
+void nilfs_dat_abort_alloc(struct inode *, struct nilfs_palloc_req *);
+int nilfs_dat_prepare_start(struct inode *, struct nilfs_palloc_req *);
+void nilfs_dat_commit_start(struct inode *, struct nilfs_palloc_req *,
+			    sector_t);
+int nilfs_dat_prepare_end(struct inode *, struct nilfs_palloc_req *);
+void nilfs_dat_commit_end(struct inode *, struct nilfs_palloc_req *, int);
+void nilfs_dat_abort_end(struct inode *, struct nilfs_palloc_req *);
+int nilfs_dat_prepare_update(struct inode *, struct nilfs_palloc_req *,
+			     struct nilfs_palloc_req *);
+void nilfs_dat_commit_update(struct inode *, struct nilfs_palloc_req *,
+			     struct nilfs_palloc_req *, int);
+void nilfs_dat_abort_update(struct inode *, struct nilfs_palloc_req *,
+			    struct nilfs_palloc_req *);
+
+int nilfs_dat_mark_dirty(struct inode *, __u64);
+int nilfs_dat_freev(struct inode *, __u64 *, size_t);
+int nilfs_dat_move(struct inode *, __u64, sector_t);
+ssize_t nilfs_dat_get_vinfo(struct inode *, void *, unsigned int, size_t);
+
+int nilfs_dat_read(struct super_block *sb, size_t entry_size,
+		   struct nilfs_inode *raw_inode, struct inode **inodep);
+
+#endif	/* _NILFS_DAT_H */