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, 146 insertions, 0 deletions

diff --git a/net/ceph/auth_none.c b/net/ceph/auth_none.c
new file mode 100644
index 000000000..99e1f3e10
--- /dev/null
+++ b/net/ceph/auth_none.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/ceph/ceph_debug.h>
+
+#include <linux/err.h>
+#include <linux/module.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+
+#include <linux/ceph/decode.h>
+#include <linux/ceph/auth.h>
+
+#include "auth_none.h"
+
+static void reset(struct ceph_auth_client *ac)
+{
+	struct ceph_auth_none_info *xi = ac->private;
+
+	xi->starting = true;
+}
+
+static void destroy(struct ceph_auth_client *ac)
+{
+	kfree(ac->private);
+	ac->private = NULL;
+}
+
+static int is_authenticated(struct ceph_auth_client *ac)
+{
+	struct ceph_auth_none_info *xi = ac->private;
+
+	return !xi->starting;
+}
+
+static int should_authenticate(struct ceph_auth_client *ac)
+{
+	struct ceph_auth_none_info *xi = ac->private;
+
+	return xi->starting;
+}
+
+static int ceph_auth_none_build_authorizer(struct ceph_auth_client *ac,
+					   struct ceph_none_authorizer *au)
+{
+	void *p = au->buf;
+	void *const end = p + sizeof(au->buf);
+	int ret;
+
+	ceph_encode_8_safe(&p, end, 1, e_range);
+	ret = ceph_auth_entity_name_encode(ac->name, &p, end);
+	if (ret < 0)
+		return ret;
+
+	ceph_encode_64_safe(&p, end, ac->global_id, e_range);
+	au->buf_len = p - (void *)au->buf;
+	dout("%s built authorizer len %d\n", __func__, au->buf_len);
+	return 0;
+
+e_range:
+	return -ERANGE;
+}
+
+static int build_request(struct ceph_auth_client *ac, void *buf, void *end)
+{
+	return 0;
+}
+
+/*
+ * the generic auth code decode the global_id, and we carry no actual
+ * authenticate state, so nothing happens here.
+ */
+static int handle_reply(struct ceph_auth_client *ac, u64 global_id,
+			void *buf, void *end, u8 *session_key,
+			int *session_key_len, u8 *con_secret,
+			int *con_secret_len)
+{
+	struct ceph_auth_none_info *xi = ac->private;
+
+	xi->starting = false;
+	ceph_auth_set_global_id(ac, global_id);
+	return 0;
+}
+
+static void ceph_auth_none_destroy_authorizer(struct ceph_authorizer *a)
+{
+	kfree(a);
+}
+
+/*
+ * build an 'authorizer' with our entity_name and global_id.  it is
+ * identical for all services we connect to.
+ */
+static int ceph_auth_none_create_authorizer(
+	struct ceph_auth_client *ac, int peer_type,
+	struct ceph_auth_handshake *auth)
+{
+	struct ceph_none_authorizer *au;
+	int ret;
+
+	au = kmalloc_obj(*au, GFP_NOFS);
+	if (!au)
+		return -ENOMEM;
+
+	au->base.destroy = ceph_auth_none_destroy_authorizer;
+
+	ret = ceph_auth_none_build_authorizer(ac, au);
+	if (ret) {
+		kfree(au);
+		return ret;
+	}
+
+	auth->authorizer = (struct ceph_authorizer *) au;
+	auth->authorizer_buf = au->buf;
+	auth->authorizer_buf_len = au->buf_len;
+	auth->authorizer_reply_buf = NULL;
+	auth->authorizer_reply_buf_len = 0;
+
+	return 0;
+}
+
+static const struct ceph_auth_client_ops ceph_auth_none_ops = {
+	.reset = reset,
+	.destroy = destroy,
+	.is_authenticated = is_authenticated,
+	.should_authenticate = should_authenticate,
+	.build_request = build_request,
+	.handle_reply = handle_reply,
+	.create_authorizer = ceph_auth_none_create_authorizer,
+};
+
+int ceph_auth_none_init(struct ceph_auth_client *ac)
+{
+	struct ceph_auth_none_info *xi;
+
+	dout("ceph_auth_none_init %p\n", ac);
+	xi = kzalloc_obj(*xi, GFP_NOFS);
+	if (!xi)
+		return -ENOMEM;
+
+	xi->starting = true;
+
+	ac->protocol = CEPH_AUTH_NONE;
+	ac->private = xi;
+	ac->ops = &ceph_auth_none_ops;
+	return 0;
+}