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, 402 insertions, 0 deletions

diff --git a/fs/coda/inode.c b/fs/coda/inode.c
new file mode 100644
index 000000000..40b43866e
--- /dev/null
+++ b/fs/coda/inode.c
@@ -0,0 +1,402 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Super block/filesystem wide operations
+ *
+ * Copyright (C) 1996 Peter J. Braam <braam@maths.ox.ac.uk> and 
+ * Michael Callahan <callahan@maths.ox.ac.uk> 
+ * 
+ * Rewritten for Linux 2.1.  Peter Braam <braam@cs.cmu.edu>
+ * Copyright (C) Carnegie Mellon University
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/stat.h>
+#include <linux/errno.h>
+#include <linux/unistd.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+#include <linux/file.h>
+#include <linux/vfs.h>
+#include <linux/slab.h>
+#include <linux/pid_namespace.h>
+#include <linux/uaccess.h>
+#include <linux/fs.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
+#include <linux/vmalloc.h>
+
+#include <linux/coda.h>
+#include "coda_psdev.h"
+#include "coda_linux.h"
+#include "coda_cache.h"
+
+#include "coda_int.h"
+
+/* VFS super_block ops */
+static void coda_evict_inode(struct inode *);
+static void coda_put_super(struct super_block *);
+static int coda_statfs(struct dentry *dentry, struct kstatfs *buf);
+
+static struct kmem_cache * coda_inode_cachep;
+
+static struct inode *coda_alloc_inode(struct super_block *sb)
+{
+	struct coda_inode_info *ei;
+	ei = alloc_inode_sb(sb, coda_inode_cachep, GFP_KERNEL);
+	if (!ei)
+		return NULL;
+	memset(&ei->c_fid, 0, sizeof(struct CodaFid));
+	ei->c_flags = 0;
+	ei->c_uid = GLOBAL_ROOT_UID;
+	ei->c_cached_perm = 0;
+	spin_lock_init(&ei->c_lock);
+	return &ei->vfs_inode;
+}
+
+static void coda_free_inode(struct inode *inode)
+{
+	kmem_cache_free(coda_inode_cachep, ITOC(inode));
+}
+
+static void init_once(void *foo)
+{
+	struct coda_inode_info *ei = (struct coda_inode_info *) foo;
+
+	inode_init_once(&ei->vfs_inode);
+}
+
+int __init coda_init_inodecache(void)
+{
+	coda_inode_cachep = kmem_cache_create("coda_inode_cache",
+				sizeof(struct coda_inode_info), 0,
+				SLAB_RECLAIM_ACCOUNT | SLAB_ACCOUNT,
+				init_once);
+	if (coda_inode_cachep == NULL)
+		return -ENOMEM;
+	return 0;
+}
+
+void coda_destroy_inodecache(void)
+{
+	/*
+	 * Make sure all delayed rcu free inodes are flushed before we
+	 * destroy cache.
+	 */
+	rcu_barrier();
+	kmem_cache_destroy(coda_inode_cachep);
+}
+
+static int coda_reconfigure(struct fs_context *fc)
+{
+	sync_filesystem(fc->root->d_sb);
+	fc->sb_flags |= SB_NOATIME;
+	return 0;
+}
+
+/* exported operations */
+static const struct super_operations coda_super_operations =
+{
+	.alloc_inode	= coda_alloc_inode,
+	.free_inode	= coda_free_inode,
+	.evict_inode	= coda_evict_inode,
+	.put_super	= coda_put_super,
+	.statfs		= coda_statfs,
+};
+
+struct coda_fs_context {
+	int	idx;
+};
+
+enum {
+	Opt_fd,
+};
+
+static const struct fs_parameter_spec coda_param_specs[] = {
+	fsparam_fd	("fd",	Opt_fd),
+	{}
+};
+
+static int coda_set_idx(struct fs_context *fc, struct file *file)
+{
+	struct coda_fs_context *ctx = fc->fs_private;
+	struct inode *inode;
+	int idx;
+
+	inode = file_inode(file);
+	if (!S_ISCHR(inode->i_mode) || imajor(inode) != CODA_PSDEV_MAJOR) {
+		return invalf(fc, "coda: Not coda psdev");
+	}
+	idx = iminor(inode);
+	if (idx < 0 || idx >= MAX_CODADEVS)
+		return invalf(fc, "coda: Bad minor number");
+	ctx->idx = idx;
+	return 0;
+}
+
+static int coda_parse_fd(struct fs_context *fc, struct fs_parameter *param,
+			 struct fs_parse_result *result)
+{
+	struct file *file;
+	int err;
+
+	if (param->type == fs_value_is_file) {
+		file = param->file;
+		param->file = NULL;
+	} else {
+		file = fget(result->uint_32);
+	}
+	if (!file)
+		return -EBADF;
+
+	err = coda_set_idx(fc, file);
+	fput(file);
+	return err;
+}
+
+static int coda_parse_param(struct fs_context *fc, struct fs_parameter *param)
+{
+	struct fs_parse_result result;
+	int opt;
+
+	opt = fs_parse(fc, coda_param_specs, param, &result);
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case Opt_fd:
+		return coda_parse_fd(fc, param, &result);
+	}
+
+	return 0;
+}
+
+/*
+ * Parse coda's binary mount data form.  We ignore any errors and go with index
+ * 0 if we get one for backward compatibility.
+ */
+static int coda_parse_monolithic(struct fs_context *fc, void *_data)
+{
+	struct file *file;
+	struct coda_mount_data *data = _data;
+
+	if (!data)
+		return invalf(fc, "coda: Bad mount data");
+
+	if (data->version != CODA_MOUNT_VERSION)
+		return invalf(fc, "coda: Bad mount version");
+
+	file = fget(data->fd);
+	if (file) {
+		coda_set_idx(fc, file);
+		fput(file);
+	}
+	return 0;
+}
+
+static int coda_fill_super(struct super_block *sb, struct fs_context *fc)
+{
+	struct coda_fs_context *ctx = fc->fs_private;
+	struct inode *root = NULL;
+	struct venus_comm *vc;
+	struct CodaFid fid;
+	int error;
+
+	infof(fc, "coda: device index: %i\n", ctx->idx);
+
+	vc = &coda_comms[ctx->idx];
+	mutex_lock(&vc->vc_mutex);
+
+	if (!vc->vc_inuse) {
+		errorf(fc, "coda: No pseudo device");
+		error = -EINVAL;
+		goto unlock_out;
+	}
+
+	if (vc->vc_sb) {
+		errorf(fc, "coda: Device already mounted");
+		error = -EBUSY;
+		goto unlock_out;
+	}
+
+	vc->vc_sb = sb;
+	mutex_unlock(&vc->vc_mutex);
+
+	sb->s_fs_info = vc;
+	sb->s_flags |= SB_NOATIME;
+	sb->s_blocksize = 4096;	/* XXXXX  what do we put here?? */
+	sb->s_blocksize_bits = 12;
+	sb->s_magic = CODA_SUPER_MAGIC;
+	sb->s_op = &coda_super_operations;
+	set_default_d_op(sb, &coda_dentry_operations);
+	sb->s_time_gran = 1;
+	sb->s_time_min = S64_MIN;
+	sb->s_time_max = S64_MAX;
+
+	error = super_setup_bdi(sb);
+	if (error)
+		goto error;
+
+	/* get root fid from Venus: this needs the root inode */
+	error = venus_rootfid(sb, &fid);
+	if ( error ) {
+		pr_warn("%s: coda_get_rootfid failed with %d\n",
+			__func__, error);
+		goto error;
+	}
+	pr_info("%s: rootfid is %s\n", __func__, coda_f2s(&fid));
+	
+	/* make root inode */
+        root = coda_cnode_make(&fid, sb);
+        if (IS_ERR(root)) {
+		error = PTR_ERR(root);
+		pr_warn("Failure of coda_cnode_make for root: error %d\n",
+			error);
+		goto error;
+	} 
+
+	pr_info("%s: rootinode is %llu dev %s\n",
+		__func__, root->i_ino, root->i_sb->s_id);
+	sb->s_root = d_make_root(root);
+	if (!sb->s_root) {
+		error = -EINVAL;
+		goto error;
+	}
+	return 0;
+
+error:
+	mutex_lock(&vc->vc_mutex);
+	vc->vc_sb = NULL;
+	sb->s_fs_info = NULL;
+unlock_out:
+	mutex_unlock(&vc->vc_mutex);
+	return error;
+}
+
+static void coda_put_super(struct super_block *sb)
+{
+	struct venus_comm *vcp = coda_vcp(sb);
+	mutex_lock(&vcp->vc_mutex);
+	vcp->vc_sb = NULL;
+	sb->s_fs_info = NULL;
+	mutex_unlock(&vcp->vc_mutex);
+	mutex_destroy(&vcp->vc_mutex);
+
+	pr_info("Bye bye.\n");
+}
+
+static void coda_evict_inode(struct inode *inode)
+{
+	truncate_inode_pages_final(&inode->i_data);
+	clear_inode(inode);
+	coda_cache_clear_inode(inode);
+}
+
+int coda_getattr(struct mnt_idmap *idmap, const struct path *path,
+		 struct kstat *stat, u32 request_mask, unsigned int flags)
+{
+	int err = coda_revalidate_inode(d_inode(path->dentry));
+	if (!err)
+		generic_fillattr(&nop_mnt_idmap, request_mask,
+				 d_inode(path->dentry), stat);
+	return err;
+}
+
+int coda_setattr(struct mnt_idmap *idmap, struct dentry *de,
+		 struct iattr *iattr)
+{
+	struct inode *inode = d_inode(de);
+	struct coda_vattr vattr;
+	int error;
+
+	memset(&vattr, 0, sizeof(vattr)); 
+
+	inode_set_ctime_current(inode);
+	coda_iattr_to_vattr(iattr, &vattr);
+	vattr.va_type = C_VNON; /* cannot set type */
+
+	/* Venus is responsible for truncating the container-file!!! */
+	error = venus_setattr(inode->i_sb, coda_i2f(inode), &vattr);
+
+	if (!error) {
+	        coda_vattr_to_iattr(inode, &vattr); 
+		coda_cache_clear_inode(inode);
+	}
+	return error;
+}
+
+const struct inode_operations coda_file_inode_operations = {
+	.permission	= coda_permission,
+	.getattr	= coda_getattr,
+	.setattr	= coda_setattr,
+};
+
+static int coda_statfs(struct dentry *dentry, struct kstatfs *buf)
+{
+	int error;
+	
+	error = venus_statfs(dentry, buf);
+
+	if (error) {
+		/* fake something like AFS does */
+		buf->f_blocks = 9000000;
+		buf->f_bfree  = 9000000;
+		buf->f_bavail = 9000000;
+		buf->f_files  = 9000000;
+		buf->f_ffree  = 9000000;
+	}
+
+	/* and fill in the rest */
+	buf->f_type = CODA_SUPER_MAGIC;
+	buf->f_bsize = 4096;
+	buf->f_namelen = CODA_MAXNAMLEN;
+
+	return 0; 
+}
+
+static int coda_get_tree(struct fs_context *fc)
+{
+	if (task_active_pid_ns(current) != &init_pid_ns)
+		return -EINVAL;
+
+	return get_tree_nodev(fc, coda_fill_super);
+}
+
+static void coda_free_fc(struct fs_context *fc)
+{
+	kfree(fc->fs_private);
+}
+
+static const struct fs_context_operations coda_context_ops = {
+	.free		= coda_free_fc,
+	.parse_param	= coda_parse_param,
+	.parse_monolithic = coda_parse_monolithic,
+	.get_tree	= coda_get_tree,
+	.reconfigure	= coda_reconfigure,
+};
+
+static int coda_init_fs_context(struct fs_context *fc)
+{
+	struct coda_fs_context *ctx;
+
+	ctx = kzalloc_obj(struct coda_fs_context);
+	if (!ctx)
+		return -ENOMEM;
+
+	fc->fs_private = ctx;
+	fc->ops = &coda_context_ops;
+	return 0;
+}
+
+struct file_system_type coda_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "coda",
+	.init_fs_context = coda_init_fs_context,
+	.parameters	= coda_param_specs,
+	.kill_sb	= kill_anon_super,
+	.fs_flags	= FS_BINARY_MOUNTDATA,
+};
+MODULE_ALIAS_FS("coda");
+