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, 63 insertions, 0 deletions

diff --git a/fs/ntfs/debug.h b/fs/ntfs/debug.h
new file mode 100644
index 000000000..d8831d492
--- /dev/null
+++ b/fs/ntfs/debug.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * NTFS kernel debug support.
+ *
+ * Copyright (c) 2001-2004 Anton Altaparmakov
+ */
+
+#ifndef _LINUX_NTFS_DEBUG_H
+#define _LINUX_NTFS_DEBUG_H
+
+#include <linux/fs.h>
+
+#include "runlist.h"
+
+#ifdef DEBUG
+
+extern int debug_msgs;
+
+extern __printf(4, 5)
+void __ntfs_debug(const char *file, int line, const char *function,
+		  const char *format, ...);
+/*
+ * ntfs_debug - write a debug level message to syslog
+ * @f:		a printf format string containing the message
+ * @...:	the variables to substitute into @f
+ *
+ * ntfs_debug() writes a DEBUG level message to the syslog but only if the
+ * driver was compiled with -DDEBUG. Otherwise, the call turns into a NOP.
+ */
+#define ntfs_debug(f, a...)						\
+	__ntfs_debug(__FILE__, __LINE__, __func__, f, ##a)
+
+void ntfs_debug_dump_runlist(const struct runlist_element *rl);
+
+#else	/* !DEBUG */
+
+#define ntfs_debug(fmt, ...)						\
+do {									\
+	if (0)								\
+		no_printk(fmt, ##__VA_ARGS__);				\
+} while (0)
+
+#define ntfs_debug_dump_runlist(rl)					\
+do {									\
+	if (0)								\
+		(void)rl;						\
+} while (0)
+
+#endif	/* !DEBUG */
+
+extern  __printf(3, 4)
+void __ntfs_warning(const char *function, const struct super_block *sb,
+		    const char *fmt, ...);
+#define ntfs_warning(sb, f, a...)	__ntfs_warning(__func__, sb, f, ##a)
+
+extern  __printf(3, 4)
+void __ntfs_error(const char *function, struct super_block *sb,
+		  const char *fmt, ...);
+#define ntfs_error(sb, f, a...)		__ntfs_error(__func__, sb, f, ##a)
+
+void ntfs_handle_error(struct super_block *sb);
+
+#endif /* _LINUX_NTFS_DEBUG_H */