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, 94 insertions, 0 deletions

diff --git a/net/ceph/msgpool.c b/net/ceph/msgpool.c
new file mode 100644
index 000000000..e3ecb80cd
--- /dev/null
+++ b/net/ceph/msgpool.c
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/ceph/ceph_debug.h>
+
+#include <linux/err.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+#include <linux/vmalloc.h>
+
+#include <linux/ceph/messenger.h>
+#include <linux/ceph/msgpool.h>
+
+static void *msgpool_alloc(gfp_t gfp_mask, void *arg)
+{
+	struct ceph_msgpool *pool = arg;
+	struct ceph_msg *msg;
+
+	msg = ceph_msg_new2(pool->type, pool->front_len, pool->max_data_items,
+			    gfp_mask, true);
+	if (!msg) {
+		dout("msgpool_alloc %s failed\n", pool->name);
+	} else {
+		dout("msgpool_alloc %s %p\n", pool->name, msg);
+		msg->pool = pool;
+	}
+	return msg;
+}
+
+static void msgpool_free(void *element, void *arg)
+{
+	struct ceph_msgpool *pool = arg;
+	struct ceph_msg *msg = element;
+
+	dout("msgpool_release %s %p\n", pool->name, msg);
+	msg->pool = NULL;
+	ceph_msg_put(msg);
+}
+
+int ceph_msgpool_init(struct ceph_msgpool *pool, int type,
+		      int front_len, int max_data_items, int size,
+		      const char *name)
+{
+	dout("msgpool %s init\n", name);
+	pool->type = type;
+	pool->front_len = front_len;
+	pool->max_data_items = max_data_items;
+	pool->pool = mempool_create(size, msgpool_alloc, msgpool_free, pool);
+	if (!pool->pool)
+		return -ENOMEM;
+	pool->name = name;
+	return 0;
+}
+
+void ceph_msgpool_destroy(struct ceph_msgpool *pool)
+{
+	dout("msgpool %s destroy\n", pool->name);
+	mempool_destroy(pool->pool);
+}
+
+struct ceph_msg *ceph_msgpool_get(struct ceph_msgpool *pool, int front_len,
+				  int max_data_items)
+{
+	struct ceph_msg *msg;
+
+	if (front_len > pool->front_len ||
+	    max_data_items > pool->max_data_items) {
+		pr_warn_ratelimited("%s need %d/%d, pool %s has %d/%d\n",
+		    __func__, front_len, max_data_items, pool->name,
+		    pool->front_len, pool->max_data_items);
+		WARN_ON_ONCE(1);
+
+		/* try to alloc a fresh message */
+		return ceph_msg_new2(pool->type, front_len, max_data_items,
+				     GFP_NOFS, false);
+	}
+
+	msg = mempool_alloc(pool->pool, GFP_NOFS);
+	dout("msgpool_get %s %p\n", pool->name, msg);
+	return msg;
+}
+
+void ceph_msgpool_put(struct ceph_msgpool *pool, struct ceph_msg *msg)
+{
+	dout("msgpool_put %s %p\n", pool->name, msg);
+
+	/* reset msg front_len; user may have changed it */
+	msg->front.iov_len = pool->front_len;
+	msg->hdr.front_len = cpu_to_le32(pool->front_len);
+
+	msg->data_length = 0;
+	msg->num_data_items = 0;
+
+	kref_init(&msg->kref);  /* retake single ref */
+	mempool_free(msg, pool->pool);
+}