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, 237 insertions, 0 deletions

diff --git a/fs/afs/main.c b/fs/afs/main.c
new file mode 100644
index 000000000..7a883c599
--- /dev/null
+++ b/fs/afs/main.c
@@ -0,0 +1,237 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* AFS client file system
+ *
+ * Copyright (C) 2002,5 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/init.h>
+#include <linux/completion.h>
+#include <linux/sched.h>
+#include <linux/random.h>
+#include <linux/proc_fs.h>
+#define CREATE_TRACE_POINTS
+#include "internal.h"
+
+MODULE_DESCRIPTION("AFS Client File System");
+MODULE_AUTHOR("Red Hat, Inc.");
+MODULE_LICENSE("GPL");
+
+unsigned afs_debug;
+module_param_named(debug, afs_debug, uint, S_IWUSR | S_IRUGO);
+MODULE_PARM_DESC(debug, "AFS debugging mask");
+
+static char *rootcell;
+
+module_param(rootcell, charp, 0);
+MODULE_PARM_DESC(rootcell, "root AFS cell name and VL server IP addr list");
+
+struct workqueue_struct *afs_wq;
+static struct proc_dir_entry *afs_proc_symlink;
+
+#if defined(CONFIG_ALPHA)
+const char afs_init_sysname[] = "alpha_linux26";
+#elif defined(CONFIG_X86_64)
+const char afs_init_sysname[] = "amd64_linux26";
+#elif defined(CONFIG_ARM)
+const char afs_init_sysname[] = "arm_linux26";
+#elif defined(CONFIG_ARM64)
+const char afs_init_sysname[] = "aarch64_linux26";
+#elif defined(CONFIG_X86_32)
+const char afs_init_sysname[] = "i386_linux26";
+#elif defined(CONFIG_PPC64)
+const char afs_init_sysname[] = "ppc64_linux26";
+#elif defined(CONFIG_PPC32)
+const char afs_init_sysname[] = "ppc_linux26";
+#elif defined(CONFIG_S390)
+#ifdef CONFIG_64BIT
+const char afs_init_sysname[] = "s390x_linux26";
+#else
+const char afs_init_sysname[] = "s390_linux26";
+#endif
+#elif defined(CONFIG_SPARC64)
+const char afs_init_sysname[] = "sparc64_linux26";
+#elif defined(CONFIG_SPARC32)
+const char afs_init_sysname[] = "sparc_linux26";
+#else
+const char afs_init_sysname[] = "unknown_linux26";
+#endif
+
+/*
+ * Initialise an AFS network namespace record.
+ */
+static int __net_init afs_net_init(struct net *net_ns)
+{
+	struct afs_sysnames *sysnames;
+	struct afs_net *net = afs_net(net_ns);
+	int ret;
+
+	net->net = net_ns;
+	net->live = true;
+	generate_random_uuid((unsigned char *)&net->uuid);
+
+	INIT_WORK(&net->charge_preallocation_work, afs_charge_preallocation);
+	INIT_WORK(&net->rx_oob_work, afs_process_oob_queue);
+	mutex_init(&net->socket_mutex);
+
+	net->cells = RB_ROOT;
+	idr_init(&net->cells_dyn_ino);
+	init_rwsem(&net->cells_lock);
+	mutex_init(&net->cells_alias_lock);
+	mutex_init(&net->proc_cells_lock);
+	INIT_HLIST_HEAD(&net->proc_cells);
+
+	seqlock_init(&net->fs_lock);
+	INIT_LIST_HEAD(&net->fs_probe_fast);
+	INIT_LIST_HEAD(&net->fs_probe_slow);
+	INIT_HLIST_HEAD(&net->fs_proc);
+
+	INIT_WORK(&net->fs_prober, afs_fs_probe_dispatcher);
+	timer_setup(&net->fs_probe_timer, afs_fs_probe_timer, 0);
+	atomic_set(&net->servers_outstanding, 1);
+
+	ret = -ENOMEM;
+	sysnames = kzalloc_obj(*sysnames);
+	if (!sysnames)
+		goto error_sysnames;
+	sysnames->subs[0] = (char *)&afs_init_sysname;
+	sysnames->nr = 1;
+	refcount_set(&sysnames->usage, 1);
+	net->sysnames = sysnames;
+	rwlock_init(&net->sysnames_lock);
+
+	/* Register the /proc stuff */
+	ret = afs_proc_init(net);
+	if (ret < 0)
+		goto error_proc;
+
+	/* Initialise the cell DB */
+	ret = afs_cell_init(net, rootcell);
+	if (ret < 0)
+		goto error_cell_init;
+
+	/* Create the RxRPC transport */
+	ret = afs_open_socket(net);
+	if (ret < 0)
+		goto error_open_socket;
+
+	return 0;
+
+error_open_socket:
+	net->live = false;
+	afs_fs_probe_cleanup(net);
+	afs_cell_purge(net);
+	afs_wait_for_servers(net);
+error_cell_init:
+	net->live = false;
+	afs_proc_cleanup(net);
+error_proc:
+	afs_put_sysnames(net->sysnames);
+error_sysnames:
+	idr_destroy(&net->cells_dyn_ino);
+	net->live = false;
+	return ret;
+}
+
+/*
+ * Clean up and destroy an AFS network namespace record.
+ */
+static void __net_exit afs_net_exit(struct net *net_ns)
+{
+	struct afs_net *net = afs_net(net_ns);
+
+	net->live = false;
+	afs_fs_probe_cleanup(net);
+	afs_cell_purge(net);
+	afs_wait_for_servers(net);
+	afs_close_socket(net);
+	afs_proc_cleanup(net);
+	afs_put_sysnames(net->sysnames);
+	idr_destroy(&net->cells_dyn_ino);
+	kfree_rcu(rcu_access_pointer(net->address_prefs), rcu);
+}
+
+static struct pernet_operations afs_net_ops = {
+	.init	= afs_net_init,
+	.exit	= afs_net_exit,
+	.id	= &afs_net_id,
+	.size	= sizeof(struct afs_net),
+};
+
+/*
+ * initialise the AFS client FS module
+ */
+static int __init afs_init(void)
+{
+	int ret = -ENOMEM;
+
+	printk(KERN_INFO "kAFS: Red Hat AFS client v0.1 registering.\n");
+
+	afs_wq = alloc_workqueue("afs", WQ_PERCPU, 0);
+	if (!afs_wq)
+		goto error_afs_wq;
+	afs_async_calls = alloc_workqueue("kafsd", WQ_MEM_RECLAIM | WQ_UNBOUND, 0);
+	if (!afs_async_calls)
+		goto error_async;
+	afs_lock_manager = alloc_workqueue("kafs_lockd", WQ_MEM_RECLAIM | WQ_PERCPU, 0);
+	if (!afs_lock_manager)
+		goto error_lockmgr;
+
+	ret = register_pernet_device(&afs_net_ops);
+	if (ret < 0)
+		goto error_net;
+
+	/* register the filesystems */
+	ret = afs_fs_init();
+	if (ret < 0)
+		goto error_fs;
+
+	afs_proc_symlink = proc_symlink("fs/afs", NULL, "../self/net/afs");
+	if (!afs_proc_symlink) {
+		ret = -ENOMEM;
+		goto error_proc;
+	}
+
+	return ret;
+
+error_proc:
+	afs_fs_exit();
+error_fs:
+	unregister_pernet_device(&afs_net_ops);
+error_net:
+	destroy_workqueue(afs_lock_manager);
+error_lockmgr:
+	destroy_workqueue(afs_async_calls);
+error_async:
+	destroy_workqueue(afs_wq);
+error_afs_wq:
+	rcu_barrier();
+	printk(KERN_ERR "kAFS: failed to register: %d\n", ret);
+	return ret;
+}
+
+/* XXX late_initcall is kludgy, but the only alternative seems to create
+ * a transport upon the first mount, which is worse. Or is it?
+ */
+late_initcall(afs_init);	/* must be called after net/ to create socket */
+
+/*
+ * clean up on module removal
+ */
+static void __exit afs_exit(void)
+{
+	printk(KERN_INFO "kAFS: Red Hat AFS client v0.1 unregistering.\n");
+
+	proc_remove(afs_proc_symlink);
+	afs_fs_exit();
+	unregister_pernet_device(&afs_net_ops);
+	destroy_workqueue(afs_lock_manager);
+	destroy_workqueue(afs_async_calls);
+	destroy_workqueue(afs_wq);
+	afs_clean_up_permit_cache();
+	rcu_barrier();
+}
+
+module_exit(afs_exit);