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, 120 insertions, 0 deletions

diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
new file mode 100644
index 000000000..e55b686fe
--- /dev/null
+++ b/fs/btrfs/acl.c
@@ -0,0 +1,120 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2007 Red Hat.  All rights reserved.
+ */
+
+#include <linux/fs.h>
+#include <linux/string.h>
+#include <linux/xattr.h>
+#include <linux/posix_acl_xattr.h>
+#include <linux/posix_acl.h>
+#include <linux/sched.h>
+#include <linux/sched/mm.h>
+#include <linux/slab.h>
+#include "ctree.h"
+#include "xattr.h"
+#include "acl.h"
+#include "misc.h"
+
+struct posix_acl *btrfs_get_acl(struct inode *inode, int type, bool rcu)
+{
+	int size;
+	const char *name;
+	char AUTO_KFREE(value);
+	struct posix_acl *acl;
+
+	if (rcu)
+		return ERR_PTR(-ECHILD);
+
+	switch (type) {
+	case ACL_TYPE_ACCESS:
+		name = XATTR_NAME_POSIX_ACL_ACCESS;
+		break;
+	case ACL_TYPE_DEFAULT:
+		name = XATTR_NAME_POSIX_ACL_DEFAULT;
+		break;
+	default:
+		return ERR_PTR(-EINVAL);
+	}
+
+	size = btrfs_getxattr(inode, name, NULL, 0);
+	if (size > 0) {
+		value = kzalloc(size, GFP_KERNEL);
+		if (!value)
+			return ERR_PTR(-ENOMEM);
+		size = btrfs_getxattr(inode, name, value, size);
+	}
+	if (size > 0)
+		acl = posix_acl_from_xattr(&init_user_ns, value, size);
+	else if (size == -ENODATA || size == 0)
+		acl = NULL;
+	else
+		acl = ERR_PTR(size);
+
+	return acl;
+}
+
+int __btrfs_set_acl(struct btrfs_trans_handle *trans, struct inode *inode,
+		    struct posix_acl *acl, int type)
+{
+	int ret;
+	size_t size = 0;
+	const char *name;
+	char AUTO_KFREE(value);
+
+	switch (type) {
+	case ACL_TYPE_ACCESS:
+		name = XATTR_NAME_POSIX_ACL_ACCESS;
+		break;
+	case ACL_TYPE_DEFAULT:
+		if (!S_ISDIR(inode->i_mode))
+			return acl ? -EINVAL : 0;
+		name = XATTR_NAME_POSIX_ACL_DEFAULT;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (acl) {
+		unsigned int nofs_flag;
+
+		/*
+		 * We're holding a transaction handle, so use a NOFS memory
+		 * allocation context to avoid deadlock if reclaim happens.
+		 */
+		nofs_flag = memalloc_nofs_save();
+		value = posix_acl_to_xattr(&init_user_ns, acl, &size, GFP_KERNEL);
+		memalloc_nofs_restore(nofs_flag);
+		if (!value)
+			return -ENOMEM;
+	}
+
+	if (trans)
+		ret = btrfs_setxattr(trans, inode, name, value, size, 0);
+	else
+		ret = btrfs_setxattr_trans(inode, name, value, size, 0);
+	if (ret < 0)
+		return ret;
+
+	set_cached_acl(inode, type, acl);
+	return 0;
+}
+
+int btrfs_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
+		  struct posix_acl *acl, int type)
+{
+	int ret;
+	struct inode *inode = d_inode(dentry);
+	umode_t old_mode = inode->i_mode;
+
+	if (type == ACL_TYPE_ACCESS && acl) {
+		ret = posix_acl_update_mode(idmap, inode,
+					    &inode->i_mode, &acl);
+		if (ret)
+			return ret;
+	}
+	ret = __btrfs_set_acl(NULL, inode, acl, type);
+	if (ret)
+		inode->i_mode = old_mode;
+	return ret;
+}