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, 134 insertions, 0 deletions

diff --git a/fs/erofs/dir.c b/fs/erofs/dir.c
new file mode 100644
index 000000000..4aa52a5f2
--- /dev/null
+++ b/fs/erofs/dir.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2017-2018 HUAWEI, Inc.
+ *             https://www.huawei.com/
+ * Copyright (C) 2022, Alibaba Cloud
+ */
+#include "internal.h"
+#include <linux/filelock.h>
+
+static int erofs_fill_dentries(struct inode *dir, struct dir_context *ctx,
+			       void *dentry_blk, struct erofs_dirent *de,
+			       unsigned int nameoff0, unsigned int maxsize)
+{
+	const struct erofs_dirent *end = dentry_blk + nameoff0;
+
+	while (de < end) {
+		unsigned char d_type = fs_ftype_to_dtype(de->file_type);
+		unsigned int nameoff = le16_to_cpu(de->nameoff);
+		const char *de_name = (char *)dentry_blk + nameoff;
+		unsigned int de_namelen;
+
+		/* non-trailing dirent in the directory block? */
+		if (de + 1 < end)
+			de_namelen = le16_to_cpu(de[1].nameoff) - nameoff;
+		else if (maxsize <= nameoff)
+			goto err_bogus;
+		else
+			de_namelen = strnlen(de_name, maxsize - nameoff);
+
+		/* a corrupted entry is found (including negative namelen) */
+		if (!in_range32(de_namelen, 1, EROFS_NAME_LEN) ||
+		    nameoff + de_namelen > maxsize)
+			goto err_bogus;
+
+		if (!dir_emit(ctx, de_name, de_namelen,
+			      erofs_nid_to_ino64(EROFS_SB(dir->i_sb),
+						 le64_to_cpu(de->nid)), d_type))
+			return 1;
+		++de;
+		ctx->pos += sizeof(struct erofs_dirent);
+	}
+	return 0;
+err_bogus:
+	erofs_err(dir->i_sb, "bogus dirent @ nid %llu", EROFS_I(dir)->nid);
+	DBG_BUGON(1);
+	return -EFSCORRUPTED;
+}
+
+static int erofs_readdir(struct file *f, struct dir_context *ctx)
+{
+	struct inode *dir = file_inode(f);
+	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
+	struct super_block *sb = dir->i_sb;
+	struct file_ra_state *ra = &f->f_ra;
+	unsigned long bsz = sb->s_blocksize;
+	unsigned int ofs = erofs_blkoff(sb, ctx->pos);
+	pgoff_t ra_pages = DIV_ROUND_UP_POW2(
+			EROFS_I_SB(dir)->dir_ra_bytes, PAGE_SIZE);
+	pgoff_t nr_pages = DIV_ROUND_UP_POW2(dir->i_size, PAGE_SIZE);
+	int err = 0;
+	bool initial = true;
+
+	buf.mapping = dir->i_mapping;
+	while (ctx->pos < dir->i_size) {
+		erofs_off_t dbstart = ctx->pos - ofs;
+		struct erofs_dirent *de;
+		unsigned int nameoff, maxsize;
+
+		if (fatal_signal_pending(current)) {
+			err = -ERESTARTSYS;
+			break;
+		}
+
+		/* readahead blocks to enhance performance for large directories */
+		if (ra_pages) {
+			pgoff_t idx = DIV_ROUND_UP_POW2(ctx->pos, PAGE_SIZE);
+			pgoff_t pages = min(nr_pages - idx, ra_pages);
+
+			if (pages > 1 && !ra_has_index(ra, idx))
+				page_cache_sync_readahead(dir->i_mapping, ra,
+							  f, idx, pages);
+		}
+
+		de = erofs_bread(&buf, dbstart, true);
+		if (IS_ERR(de)) {
+			erofs_err(sb, "failed to readdir of logical block %llu of nid %llu",
+				  erofs_blknr(sb, dbstart), EROFS_I(dir)->nid);
+			err = PTR_ERR(de);
+			break;
+		}
+
+		nameoff = le16_to_cpu(de->nameoff);
+		if (!nameoff || nameoff >= bsz || (nameoff % sizeof(*de))) {
+			erofs_err(sb, "invalid de[0].nameoff %u @ nid %llu",
+				  nameoff, EROFS_I(dir)->nid);
+			err = -EFSCORRUPTED;
+			break;
+		}
+
+		maxsize = min_t(unsigned int, dir->i_size - dbstart, bsz);
+		/* search dirents at the arbitrary position */
+		if (initial) {
+			initial = false;
+			ofs = roundup(ofs, sizeof(struct erofs_dirent));
+			ctx->pos = dbstart + ofs;
+		}
+
+		err = erofs_fill_dentries(dir, ctx, de, (void *)de + ofs,
+					  nameoff, maxsize);
+		if (err)
+			break;
+		ctx->pos = dbstart + maxsize;
+		ofs = 0;
+		cond_resched();
+	}
+	erofs_put_metabuf(&buf);
+	if (EROFS_I(dir)->dot_omitted && ctx->pos == dir->i_size) {
+		if (!dir_emit_dot(f, ctx))
+			return 0;
+		++ctx->pos;
+	}
+	return err < 0 ? err : 0;
+}
+
+const struct file_operations erofs_dir_fops = {
+	.llseek		= generic_file_llseek,
+	.read		= generic_read_dir,
+	.iterate_shared	= erofs_readdir,
+	.unlocked_ioctl = erofs_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl   = erofs_compat_ioctl,
+#endif
+	.setlease	= generic_setlease,
+};