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/jfs/acl.c b/fs/jfs/acl.c
new file mode 100644
index 000000000..16b71a23f
--- /dev/null
+++ b/fs/jfs/acl.c
@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *   Copyright (C) International Business Machines  Corp., 2002-2004
+ *   Copyright (C) Andreas Gruenbacher, 2001
+ *   Copyright (C) Linus Torvalds, 1991, 1992
+ */
+
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/fs.h>
+#include <linux/posix_acl_xattr.h>
+#include "jfs_incore.h"
+#include "jfs_txnmgr.h"
+#include "jfs_xattr.h"
+#include "jfs_acl.h"
+
+struct posix_acl *jfs_get_acl(struct inode *inode, int type, bool rcu)
+{
+	struct posix_acl *acl;
+	char *ea_name;
+	int size;
+	char *value = NULL;
+
+	if (rcu)
+		return ERR_PTR(-ECHILD);
+
+	switch(type) {
+		case ACL_TYPE_ACCESS:
+			ea_name = XATTR_NAME_POSIX_ACL_ACCESS;
+			break;
+		case ACL_TYPE_DEFAULT:
+			ea_name = XATTR_NAME_POSIX_ACL_DEFAULT;
+			break;
+		default:
+			return ERR_PTR(-EINVAL);
+	}
+
+	size = __jfs_getxattr(inode, ea_name, NULL, 0);
+
+	if (size > 0) {
+		value = kmalloc(size, GFP_KERNEL);
+		if (!value)
+			return ERR_PTR(-ENOMEM);
+		size = __jfs_getxattr(inode, ea_name, value, size);
+	}
+
+	if (size < 0) {
+		if (size == -ENODATA)
+			acl = NULL;
+		else
+			acl = ERR_PTR(size);
+	} else {
+		acl = posix_acl_from_xattr(&init_user_ns, value, size);
+	}
+	kfree(value);
+	return acl;
+}
+
+static int __jfs_set_acl(tid_t tid, struct inode *inode, int type,
+		       struct posix_acl *acl)
+{
+	char *ea_name;
+	int rc;
+	size_t size = 0;
+	char *value = NULL;
+
+	switch (type) {
+	case ACL_TYPE_ACCESS:
+		ea_name = XATTR_NAME_POSIX_ACL_ACCESS;
+		break;
+	case ACL_TYPE_DEFAULT:
+		ea_name = XATTR_NAME_POSIX_ACL_DEFAULT;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (acl) {
+		value = posix_acl_to_xattr(&init_user_ns, acl, &size, GFP_KERNEL);
+		if (!value)
+			return -ENOMEM;
+	}
+	rc = __jfs_setxattr(tid, inode, ea_name, value, size, 0);
+	kfree(value);
+
+	if (!rc)
+		set_cached_acl(inode, type, acl);
+
+	return rc;
+}
+
+int jfs_set_acl(struct mnt_idmap *idmap, struct dentry *dentry,
+		struct posix_acl *acl, int type)
+{
+	int rc;
+	tid_t tid;
+	int update_mode = 0;
+	struct inode *inode = d_inode(dentry);
+	umode_t mode = inode->i_mode;
+
+	tid = txBegin(inode->i_sb, 0);
+	mutex_lock(&JFS_IP(inode)->commit_mutex);
+	if (type == ACL_TYPE_ACCESS && acl) {
+		rc = posix_acl_update_mode(&nop_mnt_idmap, inode, &mode, &acl);
+		if (rc)
+			goto end_tx;
+		if (mode != inode->i_mode)
+			update_mode = 1;
+	}
+	rc = __jfs_set_acl(tid, inode, type, acl);
+	if (!rc) {
+		if (update_mode) {
+			inode->i_mode = mode;
+			inode_set_ctime_current(inode);
+			mark_inode_dirty(inode);
+		}
+		rc = txCommit(tid, 1, &inode, 0);
+	}
+end_tx:
+	txEnd(tid);
+	mutex_unlock(&JFS_IP(inode)->commit_mutex);
+	return rc;
+}
+
+int jfs_init_acl(tid_t tid, struct inode *inode, struct inode *dir)
+{
+	struct posix_acl *default_acl, *acl;
+	int rc = 0;
+
+	rc = posix_acl_create(dir, &inode->i_mode, &default_acl, &acl);
+	if (rc)
+		return rc;
+
+	if (default_acl) {
+		rc = __jfs_set_acl(tid, inode, ACL_TYPE_DEFAULT, default_acl);
+		posix_acl_release(default_acl);
+	} else {
+		inode->i_default_acl = NULL;
+	}
+
+	if (acl) {
+		if (!rc)
+			rc = __jfs_set_acl(tid, inode, ACL_TYPE_ACCESS, acl);
+		posix_acl_release(acl);
+	} else {
+		inode->i_acl = NULL;
+	}
+
+	JFS_IP(inode)->mode2 = (JFS_IP(inode)->mode2 & 0xffff0000) |
+			       inode->i_mode;
+
+	return rc;
+}