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, 91 insertions, 0 deletions

diff --git a/include/uapi/mtd/nftl-user.h b/include/uapi/mtd/nftl-user.h
new file mode 100644
index 000000000..b23bdc91c
--- /dev/null
+++ b/include/uapi/mtd/nftl-user.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * Copyright © 1999-2010 David Woodhouse <dwmw2@infradead.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+#ifndef __MTD_NFTL_USER_H__
+#define __MTD_NFTL_USER_H__
+
+#include <linux/types.h>
+
+/* Block Control Information */
+
+struct nftl_bci {
+	unsigned char ECCSig[6];
+	__u8 Status;
+	__u8 Status1;
+}__attribute__((packed));
+
+/* Unit Control Information */
+
+struct nftl_uci0 {
+	__u16 VirtUnitNum;
+	__u16 ReplUnitNum;
+	__u16 SpareVirtUnitNum;
+	__u16 SpareReplUnitNum;
+} __attribute__((packed));
+
+struct nftl_uci1 {
+	__u32 WearInfo;
+	__u16 EraseMark;
+	__u16 EraseMark1;
+} __attribute__((packed));
+
+struct nftl_uci2 {
+        __u16 FoldMark;
+        __u16 FoldMark1;
+	__u32 unused;
+} __attribute__((packed));
+
+union nftl_uci {
+	struct nftl_uci0 a;
+	struct nftl_uci1 b;
+	struct nftl_uci2 c;
+};
+
+struct nftl_oob {
+	struct nftl_bci b;
+	union nftl_uci u;
+};
+
+/* NFTL Media Header */
+
+struct NFTLMediaHeader {
+	char DataOrgID[6];
+	__u16 NumEraseUnits;
+	__u16 FirstPhysicalEUN;
+	__u32 FormattedSize;
+	unsigned char UnitSizeFactor;
+} __attribute__((packed));
+
+#define MAX_ERASE_ZONES (8192 - 512)
+
+#define ERASE_MARK 0x3c69
+#define SECTOR_FREE 0xff
+#define SECTOR_USED 0x55
+#define SECTOR_IGNORE 0x11
+#define SECTOR_DELETED 0x00
+
+#define FOLD_MARK_IN_PROGRESS 0x5555
+
+#define ZONE_GOOD 0xff
+#define ZONE_BAD_ORIGINAL 0
+#define ZONE_BAD_MARKED 7
+
+
+#endif /* __MTD_NFTL_USER_H__ */