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, 207 insertions, 0 deletions

diff --git a/fs/exfat/misc.c b/fs/exfat/misc.c
new file mode 100644
index 000000000..6f11a96a4
--- /dev/null
+++ b/fs/exfat/misc.c
@@ -0,0 +1,207 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Written 1992,1993 by Werner Almesberger
+ *  22/11/2000 - Fixed fat_date_unix2dos for dates earlier than 01/01/1980
+ *		 and date_dos2unix for date==0 by Igor Zhbanov(bsg@uniyar.ac.ru)
+ * Copyright (C) 2012-2013 Samsung Electronics Co., Ltd.
+ */
+
+#include <linux/time.h>
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include <linux/buffer_head.h>
+#include <linux/blk_types.h>
+
+#include "exfat_raw.h"
+#include "exfat_fs.h"
+
+/*
+ * exfat_fs_error reports a file system problem that might indicate fa data
+ * corruption/inconsistency. Depending on 'errors' mount option the
+ * panic() is called, or error message is printed FAT and nothing is done,
+ * or filesystem is remounted read-only (default behavior).
+ * In case the file system is remounted read-only, it can be made writable
+ * again by remounting it.
+ */
+void __exfat_fs_error(struct super_block *sb, int report, const char *fmt, ...)
+{
+	struct exfat_mount_options *opts = &EXFAT_SB(sb)->options;
+	va_list args;
+	struct va_format vaf;
+
+	if (report) {
+		va_start(args, fmt);
+		vaf.fmt = fmt;
+		vaf.va = &args;
+		exfat_err(sb, "error, %pV", &vaf);
+		va_end(args);
+	}
+
+	if (opts->errors == EXFAT_ERRORS_PANIC) {
+		panic("exFAT-fs (%s): fs panic from previous error\n",
+			sb->s_id);
+	} else if (opts->errors == EXFAT_ERRORS_RO && !sb_rdonly(sb)) {
+		sb->s_flags |= SB_RDONLY;
+		exfat_err(sb, "Filesystem has been set read-only");
+	}
+}
+
+#define SECS_PER_MIN    (60)
+#define TIMEZONE_SEC(x)	((x) * 15 * SECS_PER_MIN)
+
+static void exfat_adjust_tz(struct timespec64 *ts, u8 tz_off)
+{
+	if (tz_off <= 0x3F)
+		ts->tv_sec -= TIMEZONE_SEC(tz_off);
+	else /* 0x40 <= (tz_off & 0x7F) <=0x7F */
+		ts->tv_sec += TIMEZONE_SEC(0x80 - tz_off);
+}
+
+static inline int exfat_tz_offset(struct exfat_sb_info *sbi)
+{
+	if (sbi->options.sys_tz)
+		return -sys_tz.tz_minuteswest;
+	return sbi->options.time_offset;
+}
+
+/* Convert a EXFAT time/date pair to a UNIX date (seconds since 1 1 70). */
+void exfat_get_entry_time(struct exfat_sb_info *sbi, struct timespec64 *ts,
+		u8 tz, __le16 time, __le16 date, u8 time_cs)
+{
+	u16 t = le16_to_cpu(time);
+	u16 d = le16_to_cpu(date);
+
+	ts->tv_sec = mktime64(1980 + (d >> 9), d >> 5 & 0x000F, d & 0x001F,
+			      t >> 11, (t >> 5) & 0x003F, (t & 0x001F) << 1);
+
+
+	/* time_cs field represent 0 ~ 199cs(1990 ms) */
+	if (time_cs) {
+		ts->tv_sec += time_cs / 100;
+		ts->tv_nsec = (time_cs % 100) * 10 * NSEC_PER_MSEC;
+	} else
+		ts->tv_nsec = 0;
+
+	if (tz & EXFAT_TZ_VALID)
+		/* Adjust timezone to UTC0. */
+		exfat_adjust_tz(ts, tz & ~EXFAT_TZ_VALID);
+	else
+		ts->tv_sec -= exfat_tz_offset(sbi) * SECS_PER_MIN;
+}
+
+/* Convert linear UNIX date to a EXFAT time/date pair. */
+void exfat_set_entry_time(struct exfat_sb_info *sbi, struct timespec64 *ts,
+		u8 *tz, __le16 *time, __le16 *date, u8 *time_cs)
+{
+	struct tm tm;
+	u16 t, d;
+
+	time64_to_tm(ts->tv_sec, 0, &tm);
+	t = (tm.tm_hour << 11) | (tm.tm_min << 5) | (tm.tm_sec >> 1);
+	d = ((tm.tm_year - 80) <<  9) | ((tm.tm_mon + 1) << 5) | tm.tm_mday;
+
+	*time = cpu_to_le16(t);
+	*date = cpu_to_le16(d);
+
+	/* time_cs field represent 0 ~ 199cs(1990 ms) */
+	if (time_cs)
+		*time_cs = (tm.tm_sec & 1) * 100 +
+			ts->tv_nsec / (10 * NSEC_PER_MSEC);
+
+	/*
+	 * Record 00h value for OffsetFromUtc field and 1 value for OffsetValid
+	 * to indicate that local time and UTC are the same.
+	 */
+	*tz = EXFAT_TZ_VALID;
+}
+
+/*
+ * The timestamp for access_time has double seconds granularity.
+ * (There is no 10msIncrement field for access_time unlike create/modify_time)
+ * atime also has only a 2-second resolution.
+ */
+void exfat_truncate_atime(struct timespec64 *ts)
+{
+	ts->tv_sec = round_down(ts->tv_sec, 2);
+	ts->tv_nsec = 0;
+}
+
+void exfat_truncate_inode_atime(struct inode *inode)
+{
+	struct timespec64 atime = inode_get_atime(inode);
+
+	exfat_truncate_atime(&atime);
+	inode_set_atime_to_ts(inode, atime);
+}
+
+u16 exfat_calc_chksum16(void *data, int len, u16 chksum, int type)
+{
+	int i;
+	u8 *c = (u8 *)data;
+
+	for (i = 0; i < len; i++, c++) {
+		if (unlikely(type == CS_DIR_ENTRY && (i == 2 || i == 3)))
+			continue;
+		chksum = ((chksum << 15) | (chksum >> 1)) + *c;
+	}
+	return chksum;
+}
+
+u32 exfat_calc_chksum32(void *data, int len, u32 chksum, int type)
+{
+	int i;
+	u8 *c = (u8 *)data;
+
+	for (i = 0; i < len; i++, c++) {
+		if (unlikely(type == CS_BOOT_SECTOR &&
+			     (i == 106 || i == 107 || i == 112)))
+			continue;
+		chksum = ((chksum << 31) | (chksum >> 1)) + *c;
+	}
+	return chksum;
+}
+
+int exfat_update_bh(struct buffer_head *bh, int sync)
+{
+	int err = 0;
+
+	set_buffer_uptodate(bh);
+	mark_buffer_dirty(bh);
+
+	if (sync)
+		err = sync_dirty_buffer(bh);
+
+	return err;
+}
+
+int exfat_update_bhs(struct buffer_head **bhs, int nr_bhs, int sync)
+{
+	int i, err = 0;
+
+	for (i = 0; i < nr_bhs; i++) {
+		set_buffer_uptodate(bhs[i]);
+		mark_buffer_dirty(bhs[i]);
+		if (sync)
+			write_dirty_buffer(bhs[i], REQ_SYNC);
+	}
+
+	for (i = 0; i < nr_bhs && sync; i++) {
+		wait_on_buffer(bhs[i]);
+		if (!err && !buffer_uptodate(bhs[i]))
+			err = -EIO;
+	}
+	return err;
+}
+
+void exfat_chain_set(struct exfat_chain *ec, unsigned int dir,
+		unsigned int size, unsigned char flags)
+{
+	ec->dir = dir;
+	ec->size = size;
+	ec->flags = flags;
+}
+
+void exfat_chain_dup(struct exfat_chain *dup, struct exfat_chain *ec)
+{
+	return exfat_chain_set(dup, ec->dir, ec->size, ec->flags);
+}