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, 443 insertions, 0 deletions

diff --git a/fs/jffs2/super.c b/fs/jffs2/super.c
new file mode 100644
index 000000000..81396a092
--- /dev/null
+++ b/fs/jffs2/super.c
@@ -0,0 +1,443 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2001-2007 Red Hat, Inc.
+ *
+ * Created by David Woodhouse <dwmw2@infradead.org>
+ *
+ * For licensing information, see the file 'LICENCE' in this directory.
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/init.h>
+#include <linux/list.h>
+#include <linux/fs.h>
+#include <linux/err.h>
+#include <linux/mount.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/jffs2.h>
+#include <linux/pagemap.h>
+#include <linux/mtd/super.h>
+#include <linux/ctype.h>
+#include <linux/namei.h>
+#include <linux/seq_file.h>
+#include <linux/exportfs.h>
+#include "compr.h"
+#include "nodelist.h"
+
+static void jffs2_put_super(struct super_block *);
+
+static struct kmem_cache *jffs2_inode_cachep;
+
+static struct inode *jffs2_alloc_inode(struct super_block *sb)
+{
+	struct jffs2_inode_info *f;
+
+	f = alloc_inode_sb(sb, jffs2_inode_cachep, GFP_KERNEL);
+	if (!f)
+		return NULL;
+	return &f->vfs_inode;
+}
+
+static void jffs2_free_inode(struct inode *inode)
+{
+	struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);
+
+	kfree(f->target);
+	kmem_cache_free(jffs2_inode_cachep, f);
+}
+
+static void jffs2_i_init_once(void *foo)
+{
+	struct jffs2_inode_info *f = foo;
+
+	mutex_init(&f->sem);
+	f->target = NULL;
+	inode_init_once(&f->vfs_inode);
+}
+
+static const char *jffs2_compr_name(unsigned int compr)
+{
+	switch (compr) {
+	case JFFS2_COMPR_MODE_NONE:
+		return "none";
+#ifdef CONFIG_JFFS2_LZO
+	case JFFS2_COMPR_MODE_FORCELZO:
+		return "lzo";
+#endif
+#ifdef CONFIG_JFFS2_ZLIB
+	case JFFS2_COMPR_MODE_FORCEZLIB:
+		return "zlib";
+#endif
+	default:
+		/* should never happen; programmer error */
+		WARN_ON(1);
+		return "";
+	}
+}
+
+static int jffs2_show_options(struct seq_file *s, struct dentry *root)
+{
+	struct jffs2_sb_info *c = JFFS2_SB_INFO(root->d_sb);
+	struct jffs2_mount_opts *opts = &c->mount_opts;
+
+	if (opts->override_compr)
+		seq_printf(s, ",compr=%s", jffs2_compr_name(opts->compr));
+	if (opts->set_rp_size)
+		seq_printf(s, ",rp_size=%u", opts->rp_size / 1024);
+
+	return 0;
+}
+
+static int jffs2_sync_fs(struct super_block *sb, int wait)
+{
+	struct jffs2_sb_info *c = JFFS2_SB_INFO(sb);
+
+#ifdef CONFIG_JFFS2_FS_WRITEBUFFER
+	if (jffs2_is_writebuffered(c))
+		cancel_delayed_work_sync(&c->wbuf_dwork);
+#endif
+
+	mutex_lock(&c->alloc_sem);
+	jffs2_flush_wbuf_pad(c);
+	mutex_unlock(&c->alloc_sem);
+	return 0;
+}
+
+static struct inode *jffs2_nfs_get_inode(struct super_block *sb, uint64_t ino,
+					 uint32_t generation)
+{
+	/* We don't care about i_generation. We'll destroy the flash
+	   before we start re-using inode numbers anyway. And even
+	   if that wasn't true, we'd have other problems...*/
+	return jffs2_iget(sb, ino);
+}
+
+static struct dentry *jffs2_fh_to_dentry(struct super_block *sb, struct fid *fid,
+					 int fh_len, int fh_type)
+{
+        return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
+                                    jffs2_nfs_get_inode);
+}
+
+static struct dentry *jffs2_fh_to_parent(struct super_block *sb, struct fid *fid,
+					 int fh_len, int fh_type)
+{
+        return generic_fh_to_parent(sb, fid, fh_len, fh_type,
+                                    jffs2_nfs_get_inode);
+}
+
+static struct dentry *jffs2_get_parent(struct dentry *child)
+{
+	struct jffs2_inode_info *f;
+	uint32_t pino;
+
+	BUG_ON(!d_is_dir(child));
+
+	f = JFFS2_INODE_INFO(d_inode(child));
+
+	pino = f->inocache->pino_nlink;
+
+	JFFS2_DEBUG("Parent of directory ino #%u is #%u\n",
+		    f->inocache->ino, pino);
+
+	return d_obtain_alias(jffs2_iget(child->d_sb, pino));
+}
+
+static const struct export_operations jffs2_export_ops = {
+	.encode_fh = generic_encode_ino32_fh,
+	.get_parent = jffs2_get_parent,
+	.fh_to_dentry = jffs2_fh_to_dentry,
+	.fh_to_parent = jffs2_fh_to_parent,
+};
+
+/*
+ * JFFS2 mount options.
+ *
+ * Opt_source: The source device
+ * Opt_override_compr: override default compressor
+ * Opt_rp_size: size of reserved pool in KiB
+ */
+enum {
+	Opt_override_compr,
+	Opt_rp_size,
+};
+
+static const struct constant_table jffs2_param_compr[] = {
+	{"none",	JFFS2_COMPR_MODE_NONE },
+#ifdef CONFIG_JFFS2_LZO
+	{"lzo",		JFFS2_COMPR_MODE_FORCELZO },
+#endif
+#ifdef CONFIG_JFFS2_ZLIB
+	{"zlib",	JFFS2_COMPR_MODE_FORCEZLIB },
+#endif
+	{}
+};
+
+static const struct fs_parameter_spec jffs2_fs_parameters[] = {
+	fsparam_enum	("compr",	Opt_override_compr, jffs2_param_compr),
+	fsparam_u32	("rp_size",	Opt_rp_size),
+	{}
+};
+
+static int jffs2_parse_param(struct fs_context *fc, struct fs_parameter *param)
+{
+	struct fs_parse_result result;
+	struct jffs2_sb_info *c = fc->s_fs_info;
+	int opt;
+
+	opt = fs_parse(fc, jffs2_fs_parameters, param, &result);
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case Opt_override_compr:
+		c->mount_opts.compr = result.uint_32;
+		c->mount_opts.override_compr = true;
+		break;
+	case Opt_rp_size:
+		if (result.uint_32 > UINT_MAX / 1024)
+			return invalf(fc, "jffs2: rp_size unrepresentable");
+		c->mount_opts.rp_size = result.uint_32 * 1024;
+		c->mount_opts.set_rp_size = true;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static inline void jffs2_update_mount_opts(struct fs_context *fc)
+{
+	struct jffs2_sb_info *new_c = fc->s_fs_info;
+	struct jffs2_sb_info *c = JFFS2_SB_INFO(fc->root->d_sb);
+
+	mutex_lock(&c->alloc_sem);
+	if (new_c->mount_opts.override_compr) {
+		c->mount_opts.override_compr = new_c->mount_opts.override_compr;
+		c->mount_opts.compr = new_c->mount_opts.compr;
+	}
+	if (new_c->mount_opts.set_rp_size) {
+		c->mount_opts.set_rp_size = new_c->mount_opts.set_rp_size;
+		c->mount_opts.rp_size = new_c->mount_opts.rp_size;
+	}
+	mutex_unlock(&c->alloc_sem);
+}
+
+static int jffs2_reconfigure(struct fs_context *fc)
+{
+	struct super_block *sb = fc->root->d_sb;
+
+	sync_filesystem(sb);
+	jffs2_update_mount_opts(fc);
+
+	return jffs2_do_remount_fs(sb, fc);
+}
+
+static const struct super_operations jffs2_super_operations =
+{
+	.alloc_inode =	jffs2_alloc_inode,
+	.free_inode =	jffs2_free_inode,
+	.put_super =	jffs2_put_super,
+	.statfs =	jffs2_statfs,
+	.evict_inode =	jffs2_evict_inode,
+	.dirty_inode =	jffs2_dirty_inode,
+	.show_options =	jffs2_show_options,
+	.sync_fs =	jffs2_sync_fs,
+};
+
+/*
+ * fill in the superblock
+ */
+static int jffs2_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+	struct jffs2_sb_info *c = sb->s_fs_info;
+
+	jffs2_dbg(1, "jffs2_get_sb_mtd():"
+		  " New superblock for device %d (\"%s\")\n",
+		  sb->s_mtd->index, sb->s_mtd->name);
+
+	c->mtd = sb->s_mtd;
+	c->os_priv = sb;
+
+	if (c->mount_opts.rp_size > c->mtd->size)
+		return invalf(fc, "jffs2: Too large reserve pool specified, max is %llu KB",
+			      c->mtd->size / 1024);
+
+	/* Initialize JFFS2 superblock locks, the further initialization will
+	 * be done later */
+	mutex_init(&c->alloc_sem);
+	mutex_init(&c->erase_free_sem);
+	init_waitqueue_head(&c->erase_wait);
+	init_waitqueue_head(&c->inocache_wq);
+	spin_lock_init(&c->erase_completion_lock);
+	spin_lock_init(&c->inocache_lock);
+
+	sb->s_op = &jffs2_super_operations;
+	sb->s_export_op = &jffs2_export_ops;
+	sb->s_flags = sb->s_flags | SB_NOATIME;
+	sb->s_xattr = jffs2_xattr_handlers;
+#ifdef CONFIG_JFFS2_FS_POSIX_ACL
+	sb->s_flags |= SB_POSIXACL;
+#endif
+	return jffs2_do_fill_super(sb, fc);
+}
+
+static int jffs2_get_tree(struct fs_context *fc)
+{
+	return get_tree_mtd(fc, jffs2_fill_super);
+}
+
+static void jffs2_free_fc(struct fs_context *fc)
+{
+	kfree(fc->s_fs_info);
+}
+
+static const struct fs_context_operations jffs2_context_ops = {
+	.free		= jffs2_free_fc,
+	.parse_param	= jffs2_parse_param,
+	.get_tree	= jffs2_get_tree,
+	.reconfigure	= jffs2_reconfigure,
+};
+
+static int jffs2_init_fs_context(struct fs_context *fc)
+{
+	struct jffs2_sb_info *ctx;
+
+	ctx = kzalloc_obj(struct jffs2_sb_info);
+	if (!ctx)
+		return -ENOMEM;
+
+	fc->s_fs_info = ctx;
+	fc->ops = &jffs2_context_ops;
+	return 0;
+}
+
+static void jffs2_put_super (struct super_block *sb)
+{
+	struct jffs2_sb_info *c = JFFS2_SB_INFO(sb);
+
+	jffs2_dbg(2, "%s()\n", __func__);
+
+	mutex_lock(&c->alloc_sem);
+	jffs2_flush_wbuf_pad(c);
+	mutex_unlock(&c->alloc_sem);
+
+	jffs2_sum_exit(c);
+
+	jffs2_free_ino_caches(c);
+	jffs2_free_raw_node_refs(c);
+	kvfree(c->blocks);
+	jffs2_flash_cleanup(c);
+	kfree(c->inocache_list);
+	jffs2_clear_xattr_subsystem(c);
+	mtd_sync(c->mtd);
+	jffs2_dbg(1, "%s(): returning\n", __func__);
+}
+
+static void jffs2_kill_sb(struct super_block *sb)
+{
+	struct jffs2_sb_info *c = JFFS2_SB_INFO(sb);
+	if (c && !sb_rdonly(sb))
+		jffs2_stop_garbage_collect_thread(c);
+	kill_mtd_super(sb);
+	kfree(c);
+}
+
+static struct file_system_type jffs2_fs_type = {
+	.owner =	THIS_MODULE,
+	.name =		"jffs2",
+	.init_fs_context = jffs2_init_fs_context,
+	.parameters =	jffs2_fs_parameters,
+	.kill_sb =	jffs2_kill_sb,
+};
+MODULE_ALIAS_FS("jffs2");
+
+static int __init init_jffs2_fs(void)
+{
+	int ret;
+
+	/* Paranoia checks for on-medium structures. If we ask GCC
+	   to pack them with __attribute__((packed)) then it _also_
+	   assumes that they're not aligned -- so it emits crappy
+	   code on some architectures. Ideally we want an attribute
+	   which means just 'no padding', without the alignment
+	   thing. But GCC doesn't have that -- we have to just
+	   hope the structs are the right sizes, instead. */
+	BUILD_BUG_ON(sizeof(struct jffs2_unknown_node) != 12);
+	BUILD_BUG_ON(sizeof(struct jffs2_raw_dirent) != 40);
+	BUILD_BUG_ON(sizeof(struct jffs2_raw_inode) != 68);
+	BUILD_BUG_ON(sizeof(struct jffs2_raw_summary) != 32);
+
+	pr_info("version 2.2."
+#ifdef CONFIG_JFFS2_FS_WRITEBUFFER
+	       " (NAND)"
+#endif
+#ifdef CONFIG_JFFS2_SUMMARY
+	       " (SUMMARY) "
+#endif
+	       " © 2001-2006 Red Hat, Inc.\n");
+
+	jffs2_inode_cachep = kmem_cache_create("jffs2_i",
+					     sizeof(struct jffs2_inode_info),
+					     0, (SLAB_RECLAIM_ACCOUNT|
+						SLAB_ACCOUNT),
+					     jffs2_i_init_once);
+	if (!jffs2_inode_cachep) {
+		pr_err("error: Failed to initialise inode cache\n");
+		return -ENOMEM;
+	}
+	ret = jffs2_compressors_init();
+	if (ret) {
+		pr_err("error: Failed to initialise compressors\n");
+		goto out;
+	}
+	ret = jffs2_create_slab_caches();
+	if (ret) {
+		pr_err("error: Failed to initialise slab caches\n");
+		goto out_compressors;
+	}
+	ret = register_filesystem(&jffs2_fs_type);
+	if (ret) {
+		pr_err("error: Failed to register filesystem\n");
+		goto out_slab;
+	}
+	return 0;
+
+ out_slab:
+	jffs2_destroy_slab_caches();
+ out_compressors:
+	jffs2_compressors_exit();
+ out:
+	kmem_cache_destroy(jffs2_inode_cachep);
+	return ret;
+}
+
+static void __exit exit_jffs2_fs(void)
+{
+	unregister_filesystem(&jffs2_fs_type);
+	jffs2_destroy_slab_caches();
+	jffs2_compressors_exit();
+
+	/*
+	 * Make sure all delayed rcu free inodes are flushed before we
+	 * destroy cache.
+	 */
+	rcu_barrier();
+	kmem_cache_destroy(jffs2_inode_cachep);
+}
+
+module_init(init_jffs2_fs);
+module_exit(exit_jffs2_fs);
+
+MODULE_DESCRIPTION("The Journalling Flash File System, v2");
+MODULE_AUTHOR("Red Hat, Inc.");
+MODULE_LICENSE("GPL"); // Actually dual-licensed, but it doesn't matter for
+		       // the sake of this tag. It's Free Software.