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, 89 insertions, 0 deletions

diff --git a/fs/udf/udftime.c b/fs/udf/udftime.c
new file mode 100644
index 000000000..78ecc6336
--- /dev/null
+++ b/fs/udf/udftime.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: LGPL-2.0+
+/* Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Paul Eggert (eggert@twinsun.com). */
+
+/*
+ * dgb 10/02/98: ripped this from glibc source to help convert timestamps
+ *               to unix time
+ *     10/04/98: added new table-based lookup after seeing how ugly
+ *               the gnu code is
+ * blf 09/27/99: ripped out all the old code and inserted new table from
+ *		 John Brockmeyer (without leap second corrections)
+ *		 rewrote udf_stamp_to_time and fixed timezone accounting in
+ *		 udf_time_to_stamp.
+ */
+
+/*
+ * We don't take into account leap seconds. This may be correct or incorrect.
+ * For more NIST information (especially dealing with leap seconds), see:
+ * http://www.boulder.nist.gov/timefreq/pubs/bulletin/leapsecond.htm
+ */
+
+#include "udfdecl.h"
+
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/time.h>
+
+void
+udf_disk_stamp_to_time(struct timespec64 *dest, struct timestamp src)
+{
+	u16 typeAndTimezone = le16_to_cpu(src.typeAndTimezone);
+	u16 year = le16_to_cpu(src.year);
+	uint8_t type = typeAndTimezone >> 12;
+	int16_t offset;
+
+	if (type == 1) {
+		offset = typeAndTimezone << 4;
+		/* sign extent offset */
+		offset = (offset >> 4);
+		if (offset == -2047) /* unspecified offset */
+			offset = 0;
+	} else
+		offset = 0;
+
+	dest->tv_sec = mktime64(year, src.month, src.day, src.hour, src.minute,
+			src.second);
+	dest->tv_sec -= offset * 60;
+
+	/*
+	 * Sanitize nanosecond field since reportedly some filesystems are
+	 * recorded with bogus sub-second values.
+	 */
+	if (src.centiseconds < 100 && src.hundredsOfMicroseconds < 100 &&
+	    src.microseconds < 100) {
+		dest->tv_nsec = 1000 * (src.centiseconds * 10000 +
+			src.hundredsOfMicroseconds * 100 + src.microseconds);
+	} else {
+		dest->tv_nsec = 0;
+	}
+}
+
+void
+udf_time_to_disk_stamp(struct timestamp *dest, struct timespec64 ts)
+{
+	time64_t seconds;
+	int16_t offset;
+	struct tm tm;
+
+	offset = -sys_tz.tz_minuteswest;
+
+	dest->typeAndTimezone = cpu_to_le16(0x1000 | (offset & 0x0FFF));
+
+	seconds = ts.tv_sec + offset * 60;
+	time64_to_tm(seconds, 0, &tm);
+	dest->year = cpu_to_le16(tm.tm_year + 1900);
+	dest->month = tm.tm_mon + 1;
+	dest->day = tm.tm_mday;
+	dest->hour = tm.tm_hour;
+	dest->minute = tm.tm_min;
+	dest->second = tm.tm_sec;
+	dest->centiseconds = ts.tv_nsec / 10000000;
+	dest->hundredsOfMicroseconds = (ts.tv_nsec / 1000 -
+					dest->centiseconds * 10000) / 100;
+	dest->microseconds = (ts.tv_nsec / 1000 - dest->centiseconds * 10000 -
+			      dest->hundredsOfMicroseconds * 100);
+}
+
+/* EOF */