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, 153 insertions, 0 deletions

diff --git a/fs/hfs/attr.c b/fs/hfs/attr.c
new file mode 100644
index 000000000..f8395cdd1
--- /dev/null
+++ b/fs/hfs/attr.c
@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/hfs/attr.c
+ *
+ * (C) 2003 Ardis Technologies <roman@ardistech.com>
+ *
+ * Export hfs data via xattr
+ */
+
+
+#include <linux/fs.h>
+#include <linux/xattr.h>
+
+#include "hfs_fs.h"
+#include "btree.h"
+
+enum hfs_xattr_type {
+	HFS_TYPE,
+	HFS_CREATOR,
+};
+
+static int __hfs_setxattr(struct inode *inode, enum hfs_xattr_type type,
+			  const void *value, size_t size, int flags)
+{
+	struct hfs_find_data fd;
+	hfs_cat_rec rec;
+	struct hfs_cat_file *file;
+	int res;
+
+	if (!S_ISREG(inode->i_mode) || HFS_IS_RSRC(inode))
+		return -EOPNOTSUPP;
+
+	res = hfs_find_init(HFS_SB(inode->i_sb)->cat_tree, &fd);
+	if (res)
+		return res;
+	fd.search_key->cat = HFS_I(inode)->cat_key;
+	res = hfs_brec_find(&fd);
+	if (res)
+		goto out;
+	hfs_bnode_read(fd.bnode, &rec, fd.entryoffset,
+			sizeof(struct hfs_cat_file));
+	file = &rec.file;
+
+	switch (type) {
+	case HFS_TYPE:
+		if (size == 4)
+			memcpy(&file->UsrWds.fdType, value, 4);
+		else
+			res = -ERANGE;
+		break;
+
+	case HFS_CREATOR:
+		if (size == 4)
+			memcpy(&file->UsrWds.fdCreator, value, 4);
+		else
+			res = -ERANGE;
+		break;
+	}
+
+	if (!res)
+		hfs_bnode_write(fd.bnode, &rec, fd.entryoffset,
+				sizeof(struct hfs_cat_file));
+out:
+	hfs_find_exit(&fd);
+	return res;
+}
+
+static ssize_t __hfs_getxattr(struct inode *inode, enum hfs_xattr_type type,
+			      void *value, size_t size)
+{
+	struct hfs_find_data fd;
+	hfs_cat_rec rec;
+	struct hfs_cat_file *file;
+	ssize_t res = 0;
+
+	if (!S_ISREG(inode->i_mode) || HFS_IS_RSRC(inode))
+		return -EOPNOTSUPP;
+
+	if (size) {
+		res = hfs_find_init(HFS_SB(inode->i_sb)->cat_tree, &fd);
+		if (res)
+			return res;
+		fd.search_key->cat = HFS_I(inode)->cat_key;
+		res = hfs_brec_find(&fd);
+		if (res)
+			goto out;
+		hfs_bnode_read(fd.bnode, &rec, fd.entryoffset,
+				sizeof(struct hfs_cat_file));
+	}
+	file = &rec.file;
+
+	switch (type) {
+	case HFS_TYPE:
+		if (size >= 4) {
+			memcpy(value, &file->UsrWds.fdType, 4);
+			res = 4;
+		} else
+			res = size ? -ERANGE : 4;
+		break;
+
+	case HFS_CREATOR:
+		if (size >= 4) {
+			memcpy(value, &file->UsrWds.fdCreator, 4);
+			res = 4;
+		} else
+			res = size ? -ERANGE : 4;
+		break;
+	}
+
+out:
+	if (size)
+		hfs_find_exit(&fd);
+	return res;
+}
+
+static int hfs_xattr_get(const struct xattr_handler *handler,
+			 struct dentry *unused, struct inode *inode,
+			 const char *name, void *value, size_t size)
+{
+	return __hfs_getxattr(inode, handler->flags, value, size);
+}
+
+static int hfs_xattr_set(const struct xattr_handler *handler,
+			 struct mnt_idmap *idmap,
+			 struct dentry *unused, struct inode *inode,
+			 const char *name, const void *value, size_t size,
+			 int flags)
+{
+	if (!value)
+		return -EOPNOTSUPP;
+
+	return __hfs_setxattr(inode, handler->flags, value, size, flags);
+}
+
+static const struct xattr_handler hfs_creator_handler = {
+	.name = "hfs.creator",
+	.flags = HFS_CREATOR,
+	.get = hfs_xattr_get,
+	.set = hfs_xattr_set,
+};
+
+static const struct xattr_handler hfs_type_handler = {
+	.name = "hfs.type",
+	.flags = HFS_TYPE,
+	.get = hfs_xattr_get,
+	.set = hfs_xattr_set,
+};
+
+const struct xattr_handler * const hfs_xattr_handlers[] = {
+	&hfs_creator_handler,
+	&hfs_type_handler,
+	NULL
+};