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, 289 insertions, 0 deletions

diff --git a/fs/udf/misc.c b/fs/udf/misc.c
new file mode 100644
index 000000000..6928e378f
--- /dev/null
+++ b/fs/udf/misc.c
@@ -0,0 +1,289 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * misc.c
+ *
+ * PURPOSE
+ *	Miscellaneous routines for the OSTA-UDF(tm) filesystem.
+ *
+ * COPYRIGHT
+ *  (C) 1998 Dave Boynton
+ *  (C) 1998-2004 Ben Fennema
+ *  (C) 1999-2000 Stelias Computing Inc
+ *
+ * HISTORY
+ *
+ *  04/19/99 blf  partial support for reading/writing specific EA's
+ */
+
+#include "udfdecl.h"
+
+#include <linux/fs.h>
+#include <linux/string.h>
+#include <linux/crc-itu-t.h>
+
+#include "udf_i.h"
+#include "udf_sb.h"
+
+struct genericFormat *udf_add_extendedattr(struct inode *inode, uint32_t size,
+					   uint32_t type, uint8_t loc)
+{
+	uint8_t *ea = NULL, *ad = NULL;
+	int offset;
+	uint16_t crclen;
+	struct udf_inode_info *iinfo = UDF_I(inode);
+
+	ea = iinfo->i_data;
+	if (iinfo->i_lenEAttr) {
+		ad = iinfo->i_data + iinfo->i_lenEAttr;
+	} else {
+		ad = ea;
+		size += sizeof(struct extendedAttrHeaderDesc);
+	}
+
+	offset = inode->i_sb->s_blocksize - udf_file_entry_alloc_offset(inode) -
+		iinfo->i_lenAlloc;
+
+	/* TODO - Check for FreeEASpace */
+
+	if (loc & 0x01 && offset >= size) {
+		struct extendedAttrHeaderDesc *eahd;
+		eahd = (struct extendedAttrHeaderDesc *)ea;
+
+		if (iinfo->i_lenAlloc)
+			memmove(&ad[size], ad, iinfo->i_lenAlloc);
+
+		if (iinfo->i_lenEAttr) {
+			/* check checksum/crc */
+			if (eahd->descTag.tagIdent !=
+					cpu_to_le16(TAG_IDENT_EAHD) ||
+			    le32_to_cpu(eahd->descTag.tagLocation) !=
+					iinfo->i_location.logicalBlockNum)
+				return NULL;
+		} else {
+			struct udf_sb_info *sbi = UDF_SB(inode->i_sb);
+
+			size -= sizeof(struct extendedAttrHeaderDesc);
+			iinfo->i_lenEAttr +=
+				sizeof(struct extendedAttrHeaderDesc);
+			eahd->descTag.tagIdent = cpu_to_le16(TAG_IDENT_EAHD);
+			if (sbi->s_udfrev >= 0x0200)
+				eahd->descTag.descVersion = cpu_to_le16(3);
+			else
+				eahd->descTag.descVersion = cpu_to_le16(2);
+			eahd->descTag.tagSerialNum =
+					cpu_to_le16(sbi->s_serial_number);
+			eahd->descTag.tagLocation = cpu_to_le32(
+					iinfo->i_location.logicalBlockNum);
+			eahd->impAttrLocation = cpu_to_le32(0xFFFFFFFF);
+			eahd->appAttrLocation = cpu_to_le32(0xFFFFFFFF);
+		}
+
+		offset = iinfo->i_lenEAttr;
+		if (type < 2048) {
+			if (le32_to_cpu(eahd->appAttrLocation) <
+					iinfo->i_lenEAttr) {
+				uint32_t aal =
+					le32_to_cpu(eahd->appAttrLocation);
+				memmove(&ea[offset - aal + size],
+					&ea[aal], offset - aal);
+				offset -= aal;
+				eahd->appAttrLocation =
+						cpu_to_le32(aal + size);
+			}
+			if (le32_to_cpu(eahd->impAttrLocation) <
+					iinfo->i_lenEAttr) {
+				uint32_t ial =
+					le32_to_cpu(eahd->impAttrLocation);
+				memmove(&ea[offset - ial + size],
+					&ea[ial], offset - ial);
+				offset -= ial;
+				eahd->impAttrLocation =
+						cpu_to_le32(ial + size);
+			}
+		} else if (type < 65536) {
+			if (le32_to_cpu(eahd->appAttrLocation) <
+					iinfo->i_lenEAttr) {
+				uint32_t aal =
+					le32_to_cpu(eahd->appAttrLocation);
+				memmove(&ea[offset - aal + size],
+					&ea[aal], offset - aal);
+				offset -= aal;
+				eahd->appAttrLocation =
+						cpu_to_le32(aal + size);
+			}
+		}
+		/* rewrite CRC + checksum of eahd */
+		crclen = sizeof(struct extendedAttrHeaderDesc) - sizeof(struct tag);
+		eahd->descTag.descCRCLength = cpu_to_le16(crclen);
+		eahd->descTag.descCRC = cpu_to_le16(crc_itu_t(0, (char *)eahd +
+						sizeof(struct tag), crclen));
+		eahd->descTag.tagChecksum = udf_tag_checksum(&eahd->descTag);
+		iinfo->i_lenEAttr += size;
+		return (struct genericFormat *)&ea[offset];
+	}
+
+	return NULL;
+}
+
+struct genericFormat *udf_get_extendedattr(struct inode *inode, uint32_t type,
+					   uint8_t subtype)
+{
+	struct genericFormat *gaf;
+	uint8_t *ea = NULL;
+	uint32_t offset;
+	struct udf_inode_info *iinfo = UDF_I(inode);
+
+	ea = iinfo->i_data;
+
+	if (iinfo->i_lenEAttr) {
+		struct extendedAttrHeaderDesc *eahd;
+		eahd = (struct extendedAttrHeaderDesc *)ea;
+
+		/* check checksum/crc */
+		if (eahd->descTag.tagIdent !=
+				cpu_to_le16(TAG_IDENT_EAHD) ||
+		    le32_to_cpu(eahd->descTag.tagLocation) !=
+				iinfo->i_location.logicalBlockNum)
+			return NULL;
+
+		if (type < 2048)
+			offset = sizeof(struct extendedAttrHeaderDesc);
+		else if (type < 65536)
+			offset = le32_to_cpu(eahd->impAttrLocation);
+		else
+			offset = le32_to_cpu(eahd->appAttrLocation);
+
+		while (offset + sizeof(*gaf) < iinfo->i_lenEAttr) {
+			uint32_t attrLength;
+
+			gaf = (struct genericFormat *)&ea[offset];
+			attrLength = le32_to_cpu(gaf->attrLength);
+
+			/* Detect undersized elements and buffer overflows */
+			if ((attrLength < sizeof(*gaf)) ||
+			    (attrLength > (iinfo->i_lenEAttr - offset)))
+				break;
+
+			if (le32_to_cpu(gaf->attrType) == type &&
+					gaf->attrSubtype == subtype)
+				return gaf;
+			else
+				offset += attrLength;
+		}
+	}
+
+	return NULL;
+}
+
+/*
+ * udf_read_tagged
+ *
+ * PURPOSE
+ *	Read the first block of a tagged descriptor.
+ *
+ * HISTORY
+ *	July 1, 1997 - Andrew E. Mileski
+ *	Written, tested, and released.
+ */
+struct buffer_head *udf_read_tagged(struct super_block *sb, uint32_t block,
+				    uint32_t location, uint16_t *ident)
+{
+	struct tag *tag_p;
+	struct buffer_head *bh = NULL;
+	u8 checksum;
+
+	/* Read the block */
+	if (block == 0xFFFFFFFF)
+		return NULL;
+
+	bh = sb_bread(sb, block);
+	if (!bh) {
+		udf_err(sb, "read failed, block=%u, location=%u\n",
+			block, location);
+		return NULL;
+	}
+
+	tag_p = (struct tag *)(bh->b_data);
+
+	*ident = le16_to_cpu(tag_p->tagIdent);
+
+	if (location != le32_to_cpu(tag_p->tagLocation)) {
+		udf_debug("location mismatch block %u, tag %u != %u\n",
+			  block, le32_to_cpu(tag_p->tagLocation), location);
+		goto error_out;
+	}
+
+	/* Verify the tag checksum */
+	checksum = udf_tag_checksum(tag_p);
+	if (checksum != tag_p->tagChecksum) {
+		udf_err(sb, "tag checksum failed, block %u: 0x%02x != 0x%02x\n",
+			block, checksum, tag_p->tagChecksum);
+		goto error_out;
+	}
+
+	/* Verify the tag version */
+	if (tag_p->descVersion != cpu_to_le16(0x0002U) &&
+	    tag_p->descVersion != cpu_to_le16(0x0003U)) {
+		udf_err(sb, "tag version 0x%04x != 0x0002 || 0x0003, block %u\n",
+			le16_to_cpu(tag_p->descVersion), block);
+		goto error_out;
+	}
+
+	/* Verify the descriptor CRC */
+	if (le16_to_cpu(tag_p->descCRCLength) + sizeof(struct tag) > sb->s_blocksize) {
+		udf_err(sb, "block %u: CRC length %u exceeds block size\n",
+			block, le16_to_cpu(tag_p->descCRCLength));
+		goto error_out;
+	}
+	if (le16_to_cpu(tag_p->descCRC) == crc_itu_t(0,
+					bh->b_data + sizeof(struct tag),
+					le16_to_cpu(tag_p->descCRCLength)))
+		return bh;
+
+	udf_debug("Crc failure block %u: crc = %u, crclen = %u\n", block,
+		  le16_to_cpu(tag_p->descCRC),
+		  le16_to_cpu(tag_p->descCRCLength));
+error_out:
+	brelse(bh);
+	return NULL;
+}
+
+struct buffer_head *udf_read_ptagged(struct super_block *sb,
+				     struct kernel_lb_addr *loc,
+				     uint32_t offset, uint16_t *ident)
+{
+	return udf_read_tagged(sb, udf_get_lb_pblock(sb, loc, offset),
+			       loc->logicalBlockNum + offset, ident);
+}
+
+void udf_update_tag(char *data, int length)
+{
+	struct tag *tptr = (struct tag *)data;
+	length -= sizeof(struct tag);
+
+	tptr->descCRCLength = cpu_to_le16(length);
+	tptr->descCRC = cpu_to_le16(crc_itu_t(0, data + sizeof(struct tag), length));
+	tptr->tagChecksum = udf_tag_checksum(tptr);
+}
+
+void udf_new_tag(char *data, uint16_t ident, uint16_t version, uint16_t snum,
+		 uint32_t loc, int length)
+{
+	struct tag *tptr = (struct tag *)data;
+	tptr->tagIdent = cpu_to_le16(ident);
+	tptr->descVersion = cpu_to_le16(version);
+	tptr->tagSerialNum = cpu_to_le16(snum);
+	tptr->tagLocation = cpu_to_le32(loc);
+	udf_update_tag(data, length);
+}
+
+u8 udf_tag_checksum(const struct tag *t)
+{
+	u8 *data = (u8 *)t;
+	u8 checksum = 0;
+	int i;
+	for (i = 0; i < sizeof(struct tag); ++i)
+		if (i != 4) /* position of checksum */
+			checksum += data[i];
+	return checksum;
+}