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, 107 insertions, 0 deletions

diff --git a/fs/btrfs/tree-log.h b/fs/btrfs/tree-log.h
new file mode 100644
index 000000000..81ab5eeeb
--- /dev/null
+++ b/fs/btrfs/tree-log.h
@@ -0,0 +1,107 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2008 Oracle.  All rights reserved.
+ */
+
+#ifndef BTRFS_TREE_LOG_H
+#define BTRFS_TREE_LOG_H
+
+#include <linux/list.h>
+#include <linux/fs.h>
+#include <linux/fscrypt.h>
+#include "transaction.h"
+
+enum btrfs_log_mode {
+	/* Log everything about an inode. */
+	LOG_INODE_ALL,
+	/* Log just enough to recreate the inode during log replay. */
+	LOG_INODE_EXISTS,
+};
+
+struct inode;
+struct dentry;
+struct btrfs_ordered_extent;
+struct btrfs_root;
+struct btrfs_trans_handle;
+
+/* return value for btrfs_log_dentry_safe that means we don't need to log it at all */
+#define BTRFS_NO_LOG_SYNC 256
+
+/*
+ * We can't use the tree log for whatever reason, force a transaction commit.
+ * We use a negative value because there are functions through the logging code
+ * that need to return an error (< 0 value), false (0) or true (1). Any negative
+ * value will do, as it will cause the log to be marked for a full sync.
+ */
+#define BTRFS_LOG_FORCE_COMMIT				(-(MAX_ERRNO + 1))
+
+struct btrfs_log_ctx {
+	int log_ret;
+	int log_transid;
+	bool log_new_dentries;
+	bool logging_new_name;
+	bool logging_new_delayed_dentries;
+	/* Indicate if the inode being logged was logged before. */
+	bool logged_before;
+	struct btrfs_inode *inode;
+	struct list_head list;
+	/* Only used for fast fsyncs. */
+	struct list_head ordered_extents;
+	struct list_head conflict_inodes;
+	int num_conflict_inodes;
+	bool logging_conflict_inodes;
+	/*
+	 * Used for fsyncs that need to copy items from the subvolume tree to
+	 * the log tree (full sync flag set or copy everything flag set) to
+	 * avoid allocating a temporary extent buffer while holding a lock on
+	 * an extent buffer of the subvolume tree and under the log transaction.
+	 * Also helps to avoid allocating and freeing a temporary extent buffer
+	 * in case we need to process multiple leaves from the subvolume tree.
+	 */
+	struct extent_buffer *scratch_eb;
+};
+
+void btrfs_init_log_ctx(struct btrfs_log_ctx *ctx, struct btrfs_inode *inode);
+void btrfs_init_log_ctx_scratch_eb(struct btrfs_log_ctx *ctx);
+void btrfs_release_log_ctx_extents(struct btrfs_log_ctx *ctx);
+
+static inline void btrfs_set_log_full_commit(struct btrfs_trans_handle *trans)
+{
+	WRITE_ONCE(trans->fs_info->last_trans_log_full_commit, trans->transid);
+}
+
+static inline int btrfs_need_log_full_commit(struct btrfs_trans_handle *trans)
+{
+	return READ_ONCE(trans->fs_info->last_trans_log_full_commit) ==
+		trans->transid;
+}
+
+int btrfs_sync_log(struct btrfs_trans_handle *trans,
+		   struct btrfs_root *root, struct btrfs_log_ctx *ctx);
+void btrfs_free_log(struct btrfs_trans_handle *trans, struct btrfs_root *root);
+void btrfs_free_log_root_tree(struct btrfs_trans_handle *trans, struct btrfs_fs_info *fs_info);
+int btrfs_recover_log_trees(struct btrfs_root *tree_root);
+int btrfs_log_dentry_safe(struct btrfs_trans_handle *trans,
+			  struct dentry *dentry,
+			  struct btrfs_log_ctx *ctx);
+void btrfs_del_dir_entries_in_log(struct btrfs_trans_handle *trans,
+				  const struct fscrypt_str *name,
+				  struct btrfs_inode *dir, u64 index);
+void btrfs_del_inode_ref_in_log(struct btrfs_trans_handle *trans,
+				const struct fscrypt_str *name,
+				struct btrfs_inode *inode,
+				struct btrfs_inode *dir);
+void btrfs_end_log_trans(struct btrfs_root *root);
+void btrfs_pin_log_trans(struct btrfs_root *root);
+void btrfs_record_unlink_dir(struct btrfs_trans_handle *trans,
+			     struct btrfs_inode *dir, struct btrfs_inode *inode,
+			     bool for_rename);
+void btrfs_record_snapshot_destroy(struct btrfs_trans_handle *trans,
+				   struct btrfs_inode *dir);
+void btrfs_record_new_subvolume(const struct btrfs_trans_handle *trans,
+				struct btrfs_inode *dir);
+void btrfs_log_new_name(struct btrfs_trans_handle *trans,
+			struct dentry *old_dentry, struct btrfs_inode *old_dir,
+			u64 old_dir_index, struct dentry *parent);
+
+#endif