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, 179 insertions, 0 deletions

diff --git a/fs/dlm/memory.c b/fs/dlm/memory.c
new file mode 100644
index 000000000..ee55994ce
--- /dev/null
+++ b/fs/dlm/memory.c
@@ -0,0 +1,179 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/******************************************************************************
+*******************************************************************************
+**
+**  Copyright (C) Sistina Software, Inc.  1997-2003  All rights reserved.
+**  Copyright (C) 2004-2007 Red Hat, Inc.  All rights reserved.
+**
+**
+*******************************************************************************
+******************************************************************************/
+
+#include "dlm_internal.h"
+#include "midcomms.h"
+#include "lowcomms.h"
+#include "config.h"
+#include "memory.h"
+#include "ast.h"
+
+static struct kmem_cache *writequeue_cache;
+static struct kmem_cache *mhandle_cache;
+static struct kmem_cache *msg_cache;
+static struct kmem_cache *lkb_cache;
+static struct kmem_cache *rsb_cache;
+static struct kmem_cache *cb_cache;
+
+
+int __init dlm_memory_init(void)
+{
+	writequeue_cache = dlm_lowcomms_writequeue_cache_create();
+	if (!writequeue_cache)
+		goto out;
+
+	mhandle_cache = dlm_midcomms_cache_create();
+	if (!mhandle_cache)
+		goto mhandle;
+
+	lkb_cache = kmem_cache_create("dlm_lkb", sizeof(struct dlm_lkb),
+				__alignof__(struct dlm_lkb), 0, NULL);
+	if (!lkb_cache)
+		goto lkb;
+
+	msg_cache = dlm_lowcomms_msg_cache_create();
+	if (!msg_cache)
+		goto msg;
+
+	rsb_cache = kmem_cache_create("dlm_rsb", sizeof(struct dlm_rsb),
+				__alignof__(struct dlm_rsb), 0, NULL);
+	if (!rsb_cache)
+		goto rsb;
+
+	cb_cache = kmem_cache_create_usercopy("dlm_cb", sizeof(struct dlm_callback),
+				     __alignof__(struct dlm_callback), 0,
+					 offsetof(struct dlm_callback, lvbptr),
+					 sizeof_field(struct dlm_callback, lvbptr),
+				     NULL);
+	if (!cb_cache)
+		goto cb;
+
+	return 0;
+
+cb:
+	kmem_cache_destroy(rsb_cache);
+rsb:
+	kmem_cache_destroy(msg_cache);
+msg:
+	kmem_cache_destroy(lkb_cache);
+lkb:
+	kmem_cache_destroy(mhandle_cache);
+mhandle:
+	kmem_cache_destroy(writequeue_cache);
+out:
+	return -ENOMEM;
+}
+
+void dlm_memory_exit(void)
+{
+	rcu_barrier();
+
+	kmem_cache_destroy(writequeue_cache);
+	kmem_cache_destroy(mhandle_cache);
+	kmem_cache_destroy(msg_cache);
+	kmem_cache_destroy(lkb_cache);
+	kmem_cache_destroy(rsb_cache);
+	kmem_cache_destroy(cb_cache);
+}
+
+char *dlm_allocate_lvb(struct dlm_ls *ls)
+{
+	return kzalloc(ls->ls_lvblen, GFP_ATOMIC);
+}
+
+void dlm_free_lvb(char *p)
+{
+	kfree(p);
+}
+
+struct dlm_rsb *dlm_allocate_rsb(void)
+{
+	return kmem_cache_zalloc(rsb_cache, GFP_ATOMIC);
+}
+
+static void __free_rsb_rcu(struct rcu_head *rcu)
+{
+	struct dlm_rsb *r = container_of(rcu, struct dlm_rsb, rcu);
+	if (r->res_lvbptr)
+		dlm_free_lvb(r->res_lvbptr);
+	kmem_cache_free(rsb_cache, r);
+}
+
+void dlm_free_rsb(struct dlm_rsb *r)
+{
+	call_rcu(&r->rcu, __free_rsb_rcu);
+}
+
+struct dlm_lkb *dlm_allocate_lkb(void)
+{
+	return kmem_cache_zalloc(lkb_cache, GFP_ATOMIC);
+}
+
+static void __free_lkb_rcu(struct rcu_head *rcu)
+{
+	struct dlm_lkb *lkb = container_of(rcu, struct dlm_lkb, rcu);
+
+	if (test_bit(DLM_DFL_USER_BIT, &lkb->lkb_dflags)) {
+		struct dlm_user_args *ua;
+		ua = lkb->lkb_ua;
+		if (ua) {
+			kfree(ua->lksb.sb_lvbptr);
+			kfree(ua);
+		}
+	}
+
+	kmem_cache_free(lkb_cache, lkb);
+}
+
+void dlm_free_lkb(struct dlm_lkb *lkb)
+{
+	call_rcu(&lkb->rcu, __free_lkb_rcu);
+}
+
+struct dlm_mhandle *dlm_allocate_mhandle(void)
+{
+	return kmem_cache_alloc(mhandle_cache, GFP_ATOMIC);
+}
+
+void dlm_free_mhandle(struct dlm_mhandle *mhandle)
+{
+	kmem_cache_free(mhandle_cache, mhandle);
+}
+
+struct writequeue_entry *dlm_allocate_writequeue(void)
+{
+	return kmem_cache_alloc(writequeue_cache, GFP_ATOMIC);
+}
+
+void dlm_free_writequeue(struct writequeue_entry *writequeue)
+{
+	kmem_cache_free(writequeue_cache, writequeue);
+}
+
+struct dlm_msg *dlm_allocate_msg(void)
+{
+	return kmem_cache_alloc(msg_cache, GFP_ATOMIC);
+}
+
+void dlm_free_msg(struct dlm_msg *msg)
+{
+	kmem_cache_free(msg_cache, msg);
+}
+
+struct dlm_callback *dlm_allocate_cb(void)
+{
+	return kmem_cache_alloc(cb_cache, GFP_ATOMIC);
+}
+
+void dlm_free_cb(struct dlm_callback *cb)
+{
+	kmem_cache_free(cb_cache, cb);
+}