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, 112 insertions, 0 deletions

diff --git a/fs/ceph/cache.c b/fs/ceph/cache.c
new file mode 100644
index 000000000..f678bab18
--- /dev/null
+++ b/fs/ceph/cache.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Ceph cache definitions.
+ *
+ *  Copyright (C) 2013 by Adfin Solutions, Inc. All Rights Reserved.
+ *  Written by Milosz Tanski (milosz@adfin.com)
+ */
+
+#include <linux/ceph/ceph_debug.h>
+
+#include <linux/fs_context.h>
+#include "super.h"
+#include "cache.h"
+
+void ceph_fscache_register_inode_cookie(struct inode *inode)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	struct ceph_fs_client *fsc = ceph_inode_to_fs_client(inode);
+
+	/* No caching for filesystem? */
+	if (!fsc->fscache)
+		return;
+
+	/* Regular files only */
+	if (!S_ISREG(inode->i_mode))
+		return;
+
+	/* Only new inodes! */
+	if (!(inode_state_read_once(inode) & I_NEW))
+		return;
+
+	WARN_ON_ONCE(ci->netfs.cache);
+
+	ci->netfs.cache =
+		fscache_acquire_cookie(fsc->fscache, 0,
+				       &ci->i_vino, sizeof(ci->i_vino),
+				       &ci->i_version, sizeof(ci->i_version),
+				       i_size_read(inode));
+	if (ci->netfs.cache)
+		mapping_set_release_always(inode->i_mapping);
+}
+
+void ceph_fscache_unregister_inode_cookie(struct ceph_inode_info *ci)
+{
+	fscache_relinquish_cookie(ceph_fscache_cookie(ci), false);
+}
+
+void ceph_fscache_use_cookie(struct inode *inode, bool will_modify)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+
+	fscache_use_cookie(ceph_fscache_cookie(ci), will_modify);
+}
+
+void ceph_fscache_unuse_cookie(struct inode *inode, bool update)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+
+	if (update) {
+		loff_t i_size = i_size_read(inode);
+
+		fscache_unuse_cookie(ceph_fscache_cookie(ci),
+				     &ci->i_version, &i_size);
+	} else {
+		fscache_unuse_cookie(ceph_fscache_cookie(ci), NULL, NULL);
+	}
+}
+
+void ceph_fscache_update(struct inode *inode)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+	loff_t i_size = i_size_read(inode);
+
+	fscache_update_cookie(ceph_fscache_cookie(ci), &ci->i_version, &i_size);
+}
+
+void ceph_fscache_invalidate(struct inode *inode, bool dio_write)
+{
+	struct ceph_inode_info *ci = ceph_inode(inode);
+
+	fscache_invalidate(ceph_fscache_cookie(ci),
+			   &ci->i_version, i_size_read(inode),
+			   dio_write ? FSCACHE_INVAL_DIO_WRITE : 0);
+}
+
+int ceph_fscache_register_fs(struct ceph_fs_client* fsc, struct fs_context *fc)
+{
+	const struct ceph_fsid *fsid = &fsc->client->fsid;
+	const char *fscache_uniq = fsc->mount_options->fscache_uniq;
+	size_t uniq_len = fscache_uniq ? strlen(fscache_uniq) : 0;
+	char *name;
+	int err = 0;
+
+	name = kasprintf(GFP_KERNEL, "ceph,%pU%s%s", fsid, uniq_len ? "," : "",
+			 uniq_len ? fscache_uniq : "");
+	if (!name)
+		return -ENOMEM;
+
+	fsc->fscache = fscache_acquire_volume(name, NULL, NULL, 0);
+	if (IS_ERR_OR_NULL(fsc->fscache)) {
+		errorfc(fc, "Unable to register fscache cookie for %s", name);
+		err = fsc->fscache ? PTR_ERR(fsc->fscache) : -EOPNOTSUPP;
+		fsc->fscache = NULL;
+	}
+	kfree(name);
+	return err;
+}
+
+void ceph_fscache_unregister_fs(struct ceph_fs_client* fsc)
+{
+	fscache_relinquish_volume(fsc->fscache, NULL, false);
+}