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, 336 insertions, 0 deletions

diff --git a/fs/jffs2/file.c b/fs/jffs2/file.c
new file mode 100644
index 000000000..1e18d3a79
--- /dev/null
+++ b/fs/jffs2/file.c
@@ -0,0 +1,336 @@
+/*
+ * JFFS2 -- Journalling Flash File System, Version 2.
+ *
+ * Copyright © 2001-2007 Red Hat, Inc.
+ * Copyright © 2004-2010 David Woodhouse <dwmw2@infradead.org>
+ *
+ * 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/fs.h>
+#include <linux/filelock.h>
+#include <linux/time.h>
+#include <linux/pagemap.h>
+#include <linux/highmem.h>
+#include <linux/crc32.h>
+#include <linux/jffs2.h>
+#include "nodelist.h"
+
+static int jffs2_write_end(const struct kiocb *iocb,
+			   struct address_space *mapping,
+			   loff_t pos, unsigned len, unsigned copied,
+			   struct folio *folio, void *fsdata);
+static int jffs2_write_begin(const struct kiocb *iocb,
+			     struct address_space *mapping,
+			     loff_t pos, unsigned len,
+			     struct folio **foliop, void **fsdata);
+static int jffs2_read_folio(struct file *filp, struct folio *folio);
+
+int jffs2_fsync(struct file *filp, loff_t start, loff_t end, int datasync)
+{
+	struct inode *inode = filp->f_mapping->host;
+	struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);
+	int ret;
+
+	ret = file_write_and_wait_range(filp, start, end);
+	if (ret)
+		return ret;
+
+	inode_lock(inode);
+	/* Trigger GC to flush any pending writes for this inode */
+	jffs2_flush_wbuf_gc(c, inode->i_ino);
+	inode_unlock(inode);
+
+	return 0;
+}
+
+const struct file_operations jffs2_file_operations =
+{
+	.llseek =	generic_file_llseek,
+	.open =		generic_file_open,
+ 	.read_iter =	generic_file_read_iter,
+ 	.write_iter =	generic_file_write_iter,
+	.unlocked_ioctl=jffs2_ioctl,
+	.mmap_prepare =	generic_file_readonly_mmap_prepare,
+	.fsync =	jffs2_fsync,
+	.splice_read =	filemap_splice_read,
+	.splice_write = iter_file_splice_write,
+	.setlease =	generic_setlease,
+};
+
+/* jffs2_file_inode_operations */
+
+const struct inode_operations jffs2_file_inode_operations =
+{
+	.get_inode_acl =	jffs2_get_acl,
+	.set_acl =	jffs2_set_acl,
+	.setattr =	jffs2_setattr,
+	.listxattr =	jffs2_listxattr,
+};
+
+const struct address_space_operations jffs2_file_address_operations =
+{
+	.read_folio =	jffs2_read_folio,
+	.write_begin =	jffs2_write_begin,
+	.write_end =	jffs2_write_end,
+};
+
+static int jffs2_do_readpage_nolock(struct inode *inode, struct folio *folio)
+{
+	struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);
+	struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);
+	unsigned char *kaddr;
+	int ret;
+
+	jffs2_dbg(2, "%s(): ino #%llu, page at offset 0x%lx\n",
+		  __func__, inode->i_ino, folio->index << PAGE_SHIFT);
+
+	BUG_ON(!folio_test_locked(folio));
+
+	kaddr = kmap_local_folio(folio, 0);
+	ret = jffs2_read_inode_range(c, f, kaddr, folio->index << PAGE_SHIFT,
+				     PAGE_SIZE);
+	kunmap_local(kaddr);
+
+	if (!ret)
+		folio_mark_uptodate(folio);
+
+	flush_dcache_folio(folio);
+
+	jffs2_dbg(2, "readpage finished\n");
+	return ret;
+}
+
+int __jffs2_read_folio(struct file *file, struct folio *folio)
+{
+	int ret = jffs2_do_readpage_nolock(folio->mapping->host, folio);
+	folio_unlock(folio);
+	return ret;
+}
+
+static int jffs2_read_folio(struct file *file, struct folio *folio)
+{
+	struct jffs2_inode_info *f = JFFS2_INODE_INFO(folio->mapping->host);
+	int ret;
+
+	mutex_lock(&f->sem);
+	ret = __jffs2_read_folio(file, folio);
+	mutex_unlock(&f->sem);
+	return ret;
+}
+
+static int jffs2_write_begin(const struct kiocb *iocb,
+			     struct address_space *mapping,
+			     loff_t pos, unsigned len,
+			     struct folio **foliop, void **fsdata)
+{
+	struct folio *folio;
+	struct inode *inode = mapping->host;
+	struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);
+	struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);
+	pgoff_t index = pos >> PAGE_SHIFT;
+	int ret = 0;
+
+	jffs2_dbg(1, "%s()\n", __func__);
+
+	if (pos > inode->i_size) {
+		/* Make new hole frag from old EOF to new position */
+		struct jffs2_raw_inode ri;
+		struct jffs2_full_dnode *fn;
+		uint32_t alloc_len;
+
+		jffs2_dbg(1, "Writing new hole frag 0x%x-0x%x between current EOF and new position\n",
+			  (unsigned int)inode->i_size, (uint32_t)pos);
+
+		ret = jffs2_reserve_space(c, sizeof(ri), &alloc_len,
+					  ALLOC_NORMAL, JFFS2_SUMMARY_INODE_SIZE);
+		if (ret)
+			goto out_err;
+
+		mutex_lock(&f->sem);
+		memset(&ri, 0, sizeof(ri));
+
+		ri.magic = cpu_to_je16(JFFS2_MAGIC_BITMASK);
+		ri.nodetype = cpu_to_je16(JFFS2_NODETYPE_INODE);
+		ri.totlen = cpu_to_je32(sizeof(ri));
+		ri.hdr_crc = cpu_to_je32(crc32(0, &ri, sizeof(struct jffs2_unknown_node)-4));
+
+		ri.ino = cpu_to_je32(f->inocache->ino);
+		ri.version = cpu_to_je32(++f->highest_version);
+		ri.mode = cpu_to_jemode(inode->i_mode);
+		ri.uid = cpu_to_je16(i_uid_read(inode));
+		ri.gid = cpu_to_je16(i_gid_read(inode));
+		ri.isize = cpu_to_je32((uint32_t)pos);
+		ri.atime = ri.ctime = ri.mtime = cpu_to_je32(JFFS2_NOW());
+		ri.offset = cpu_to_je32(inode->i_size);
+		ri.dsize = cpu_to_je32((uint32_t)pos - inode->i_size);
+		ri.csize = cpu_to_je32(0);
+		ri.compr = JFFS2_COMPR_ZERO;
+		ri.node_crc = cpu_to_je32(crc32(0, &ri, sizeof(ri)-8));
+		ri.data_crc = cpu_to_je32(0);
+
+		fn = jffs2_write_dnode(c, f, &ri, NULL, 0, ALLOC_NORMAL);
+
+		if (IS_ERR(fn)) {
+			ret = PTR_ERR(fn);
+			jffs2_complete_reservation(c);
+			mutex_unlock(&f->sem);
+			goto out_err;
+		}
+		ret = jffs2_add_full_dnode_to_inode(c, f, fn);
+		if (f->metadata) {
+			jffs2_mark_node_obsolete(c, f->metadata->raw);
+			jffs2_free_full_dnode(f->metadata);
+			f->metadata = NULL;
+		}
+		if (ret) {
+			jffs2_dbg(1, "Eep. add_full_dnode_to_inode() failed in write_begin, returned %d\n",
+				  ret);
+			jffs2_mark_node_obsolete(c, fn->raw);
+			jffs2_free_full_dnode(fn);
+			jffs2_complete_reservation(c);
+			mutex_unlock(&f->sem);
+			goto out_err;
+		}
+		jffs2_complete_reservation(c);
+		inode->i_size = pos;
+		mutex_unlock(&f->sem);
+	}
+
+	/*
+	 * While getting a page and reading data in, lock c->alloc_sem until
+	 * the page is Uptodate. Otherwise GC task may attempt to read the same
+	 * page in read_cache_page(), which causes a deadlock.
+	 */
+	mutex_lock(&c->alloc_sem);
+	folio = __filemap_get_folio(mapping, index, FGP_WRITEBEGIN,
+			mapping_gfp_mask(mapping));
+	if (IS_ERR(folio)) {
+		ret = PTR_ERR(folio);
+		goto release_sem;
+	}
+	*foliop = folio;
+
+	/*
+	 * Read in the folio if it wasn't already present. Cannot optimize away
+	 * the whole folio write case until jffs2_write_end can handle the
+	 * case of a short-copy.
+	 */
+	if (!folio_test_uptodate(folio)) {
+		mutex_lock(&f->sem);
+		ret = jffs2_do_readpage_nolock(inode, folio);
+		mutex_unlock(&f->sem);
+		if (ret) {
+			folio_unlock(folio);
+			folio_put(folio);
+			goto release_sem;
+		}
+	}
+	jffs2_dbg(1, "end write_begin(). folio->flags %lx\n", folio->flags.f);
+
+release_sem:
+	mutex_unlock(&c->alloc_sem);
+out_err:
+	return ret;
+}
+
+static int jffs2_write_end(const struct kiocb *iocb,
+			   struct address_space *mapping,
+			   loff_t pos, unsigned len, unsigned copied,
+			   struct folio *folio, void *fsdata)
+{
+	/* Actually commit the write from the page cache page we're looking at.
+	 * For now, we write the full page out each time. It sucks, but it's simple
+	 */
+	struct inode *inode = mapping->host;
+	struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);
+	struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);
+	struct jffs2_raw_inode *ri;
+	unsigned start = pos & (PAGE_SIZE - 1);
+	unsigned end = start + copied;
+	unsigned aligned_start = start & ~3;
+	int ret = 0;
+	uint32_t writtenlen = 0;
+	void *buf;
+
+	jffs2_dbg(1, "%s(): ino #%llu, page at 0x%llx, range %d-%d, flags %lx\n",
+		  __func__, inode->i_ino, folio_pos(folio),
+		  start, end, folio->flags.f);
+
+	/* We need to avoid deadlock with page_cache_read() in
+	   jffs2_garbage_collect_pass(). So the folio must be
+	   up to date to prevent page_cache_read() from trying
+	   to re-lock it. */
+	BUG_ON(!folio_test_uptodate(folio));
+
+	if (end == PAGE_SIZE) {
+		/* When writing out the end of a page, write out the
+		   _whole_ page. This helps to reduce the number of
+		   nodes in files which have many short writes, like
+		   syslog files. */
+		aligned_start = 0;
+	}
+
+	ri = jffs2_alloc_raw_inode();
+
+	if (!ri) {
+		jffs2_dbg(1, "%s(): Allocation of raw inode failed\n",
+			  __func__);
+		folio_unlock(folio);
+		folio_put(folio);
+		return -ENOMEM;
+	}
+
+	/* Set the fields that the generic jffs2_write_inode_range() code can't find */
+	ri->ino = cpu_to_je32(inode->i_ino);
+	ri->mode = cpu_to_jemode(inode->i_mode);
+	ri->uid = cpu_to_je16(i_uid_read(inode));
+	ri->gid = cpu_to_je16(i_gid_read(inode));
+	ri->isize = cpu_to_je32((uint32_t)inode->i_size);
+	ri->atime = ri->ctime = ri->mtime = cpu_to_je32(JFFS2_NOW());
+
+	buf = kmap_local_folio(folio, aligned_start);
+	ret = jffs2_write_inode_range(c, f, ri, buf,
+				      folio_pos(folio) + aligned_start,
+				      end - aligned_start, &writtenlen);
+	kunmap_local(buf);
+
+	if (ret)
+		mapping_set_error(mapping, ret);
+
+	/* Adjust writtenlen for the padding we did, so we don't confuse our caller */
+	writtenlen -= min(writtenlen, (start - aligned_start));
+
+	if (writtenlen) {
+		if (inode->i_size < pos + writtenlen) {
+			inode->i_size = pos + writtenlen;
+			inode->i_blocks = (inode->i_size + 511) >> 9;
+
+			inode_set_mtime_to_ts(inode,
+					      inode_set_ctime_to_ts(inode, ITIME(je32_to_cpu(ri->ctime))));
+		}
+	}
+
+	jffs2_free_raw_inode(ri);
+
+	if (start+writtenlen < end) {
+		/* generic_file_write has written more to the page cache than we've
+		   actually written to the medium. Mark the page !Uptodate so that
+		   it gets reread */
+		jffs2_dbg(1, "%s(): Not all bytes written. Marking page !uptodate\n",
+			__func__);
+		folio_clear_uptodate(folio);
+	}
+
+	jffs2_dbg(1, "%s() returning %d\n",
+		  __func__, writtenlen > 0 ? writtenlen : ret);
+	folio_unlock(folio);
+	folio_put(folio);
+	return writtenlen > 0 ? writtenlen : ret;
+}