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, 87 insertions, 0 deletions

diff --git a/fs/ntfs/time.h b/fs/ntfs/time.h
new file mode 100644
index 000000000..aeed195bd
--- /dev/null
+++ b/fs/ntfs/time.h
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * NTFS time conversion functions.
+ *
+ * Copyright (c) 2001-2005 Anton Altaparmakov
+ */
+
+#ifndef _LINUX_NTFS_TIME_H
+#define _LINUX_NTFS_TIME_H
+
+#include <linux/time.h>
+#include <asm/div64.h>		/* For do_div(). */
+
+#define NTFS_TIME_OFFSET ((s64)(369 * 365 + 89) * 24 * 3600)
+
+/*
+ * utc2ntfs - convert Linux UTC time to NTFS time
+ * @ts:		Linux UTC time to convert to NTFS time
+ *
+ * Convert the Linux UTC time @ts to its corresponding NTFS time and return
+ * that in little endian format.
+ *
+ * Linux stores time in a struct timespec64 consisting of a time64_t tv_sec
+ * and a long tv_nsec where tv_sec is the number of 1-second intervals since
+ * 1st January 1970, 00:00:00 UTC and tv_nsec is the number of 1-nano-second
+ * intervals since the value of tv_sec.
+ *
+ * NTFS uses Microsoft's standard time format which is stored in a s64 and is
+ * measured as the number of 100-nano-second intervals since 1st January 1601,
+ * 00:00:00 UTC.
+ */
+static inline __le64 utc2ntfs(const struct timespec64 ts)
+{
+	/*
+	 * Convert the seconds to 100ns intervals, add the nano-seconds
+	 * converted to 100ns intervals, and then add the NTFS time offset.
+	 */
+	return cpu_to_le64((u64)(ts.tv_sec + NTFS_TIME_OFFSET) * 10000000 +
+			ts.tv_nsec / 100);
+}
+
+/*
+ * get_current_ntfs_time - get the current time in little endian NTFS format
+ *
+ * Get the current time from the Linux kernel, convert it to its corresponding
+ * NTFS time and return that in little endian format.
+ */
+static inline __le64 get_current_ntfs_time(void)
+{
+	struct timespec64 ts;
+
+	ktime_get_coarse_real_ts64(&ts);
+	return utc2ntfs(ts);
+}
+
+/*
+ * ntfs2utc - convert NTFS time to Linux time
+ * @time:	NTFS time (little endian) to convert to Linux UTC
+ *
+ * Convert the little endian NTFS time @time to its corresponding Linux UTC
+ * time and return that in cpu format.
+ *
+ * Linux stores time in a struct timespec64 consisting of a time64_t tv_sec
+ * and a long tv_nsec where tv_sec is the number of 1-second intervals since
+ * 1st January 1970, 00:00:00 UTC and tv_nsec is the number of 1-nano-second
+ * intervals since the value of tv_sec.
+ *
+ * NTFS uses Microsoft's standard time format which is stored in a s64 and is
+ * measured as the number of 100 nano-second intervals since 1st January 1601,
+ * 00:00:00 UTC.
+ */
+static inline struct timespec64 ntfs2utc(const __le64 time)
+{
+	struct timespec64 ts;
+	s32 t32;
+
+	/* Subtract the NTFS time offset. */
+	s64 t = le64_to_cpu(time) - NTFS_TIME_OFFSET * 10000000;
+	/*
+	 * Convert the time to 1-second intervals and the remainder to
+	 * 1-nano-second intervals.
+	 */
+	ts.tv_sec = div_s64_rem(t, 10000000, &t32);
+	ts.tv_nsec = t32 * 100;
+	return ts;
+}
+#endif /* _LINUX_NTFS_TIME_H */