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, 113 insertions, 0 deletions

diff --git a/fs/udf/ialloc.c b/fs/udf/ialloc.c
new file mode 100644
index 000000000..5f1f969f4
--- /dev/null
+++ b/fs/udf/ialloc.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ialloc.c
+ *
+ * PURPOSE
+ *	Inode allocation handling routines for the OSTA-UDF(tm) filesystem.
+ *
+ * COPYRIGHT
+ *  (C) 1998-2001 Ben Fennema
+ *
+ * HISTORY
+ *
+ *  02/24/99 blf  Created.
+ *
+ */
+
+#include "udfdecl.h"
+#include <linux/fs.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+
+#include "udf_i.h"
+#include "udf_sb.h"
+
+void udf_free_inode(struct inode *inode)
+{
+	udf_free_blocks(inode->i_sb, NULL, &UDF_I(inode)->i_location, 0, 1);
+}
+
+struct inode *udf_new_inode(struct inode *dir, umode_t mode)
+{
+	struct super_block *sb = dir->i_sb;
+	struct udf_sb_info *sbi = UDF_SB(sb);
+	struct inode *inode;
+	udf_pblk_t block;
+	uint32_t start = UDF_I(dir)->i_location.logicalBlockNum;
+	struct udf_inode_info *iinfo;
+	struct udf_inode_info *dinfo = UDF_I(dir);
+	int err;
+
+	inode = new_inode(sb);
+
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	iinfo = UDF_I(inode);
+	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_EXTENDED_FE)) {
+		iinfo->i_efe = 1;
+		if (UDF_VERS_USE_EXTENDED_FE > sbi->s_udfrev)
+			sbi->s_udfrev = UDF_VERS_USE_EXTENDED_FE;
+		iinfo->i_data = kzalloc(inode->i_sb->s_blocksize -
+					sizeof(struct extendedFileEntry),
+					GFP_KERNEL);
+	} else {
+		iinfo->i_efe = 0;
+		iinfo->i_data = kzalloc(inode->i_sb->s_blocksize -
+					sizeof(struct fileEntry),
+					GFP_KERNEL);
+	}
+	if (!iinfo->i_data) {
+		make_bad_inode(inode);
+		iput(inode);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	err = -ENOSPC;
+	block = udf_new_block(dir->i_sb, NULL,
+			      dinfo->i_location.partitionReferenceNum,
+			      start, &err);
+	if (err) {
+		make_bad_inode(inode);
+		iput(inode);
+		return ERR_PTR(err);
+	}
+
+	iinfo->i_unique = lvid_get_unique_id(sb);
+	inode->i_generation = iinfo->i_unique;
+
+	inode_init_owner(&nop_mnt_idmap, inode, dir, mode);
+	if (UDF_QUERY_FLAG(sb, UDF_FLAG_UID_SET))
+		inode->i_uid = sbi->s_uid;
+	if (UDF_QUERY_FLAG(sb, UDF_FLAG_GID_SET))
+		inode->i_gid = sbi->s_gid;
+
+	iinfo->i_location.logicalBlockNum = block;
+	iinfo->i_location.partitionReferenceNum =
+				dinfo->i_location.partitionReferenceNum;
+	inode->i_ino = udf_get_lb_pblock(sb, &iinfo->i_location, 0);
+	inode->i_blocks = 0;
+	iinfo->i_lenEAttr = 0;
+	iinfo->i_lenAlloc = 0;
+	iinfo->i_use = 0;
+	iinfo->i_checkpoint = 1;
+	iinfo->i_extraPerms = FE_PERM_U_CHATTR;
+	udf_update_extra_perms(inode, mode);
+
+	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_AD_IN_ICB))
+		iinfo->i_alloc_type = ICBTAG_FLAG_AD_IN_ICB;
+	else if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_SHORT_AD))
+		iinfo->i_alloc_type = ICBTAG_FLAG_AD_SHORT;
+	else
+		iinfo->i_alloc_type = ICBTAG_FLAG_AD_LONG;
+	simple_inode_init_ts(inode);
+	iinfo->i_crtime = inode_get_mtime(inode);
+	if (unlikely(insert_inode_locked(inode) < 0)) {
+		make_bad_inode(inode);
+		iput(inode);
+		return ERR_PTR(-EIO);
+	}
+	mark_inode_dirty(inode);
+
+	return inode;
+}