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, 127 insertions, 0 deletions

diff --git a/block/partitions/sun.c b/block/partitions/sun.c
new file mode 100644
index 000000000..92c645fcd
--- /dev/null
+++ b/block/partitions/sun.c
@@ -0,0 +1,127 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  fs/partitions/sun.c
+ *
+ *  Code extracted from drivers/block/genhd.c
+ *
+ *  Copyright (C) 1991-1998  Linus Torvalds
+ *  Re-organised Feb 1998 Russell King
+ */
+
+#include "check.h"
+
+#define SUN_LABEL_MAGIC          0xDABE
+#define SUN_VTOC_SANITY          0x600DDEEE
+
+enum {
+	SUN_WHOLE_DISK = 5,
+	LINUX_RAID_PARTITION = 0xfd,	/* autodetect RAID partition */
+};
+
+int sun_partition(struct parsed_partitions *state)
+{
+	int i;
+	__be16 csum;
+	int slot = 1;
+	__be16 *ush;
+	Sector sect;
+	struct sun_disklabel {
+		unsigned char info[128];   /* Informative text string */
+		struct sun_vtoc {
+		    __be32 version;     /* Layout version */
+		    char   volume[8];   /* Volume name */
+		    __be16 nparts;      /* Number of partitions */
+		    struct sun_info {           /* Partition hdrs, sec 2 */
+			__be16 id;
+			__be16 flags;
+		    } infos[8];
+		    __be16 padding;     /* Alignment padding */
+		    __be32 bootinfo[3];  /* Info needed by mboot */
+		    __be32 sanity;       /* To verify vtoc sanity */
+		    __be32 reserved[10]; /* Free space */
+		    __be32 timestamp[8]; /* Partition timestamp */
+		} vtoc;
+		__be32 write_reinstruct; /* sectors to skip, writes */
+		__be32 read_reinstruct;  /* sectors to skip, reads */
+		unsigned char spare[148]; /* Padding */
+		__be16 rspeed;     /* Disk rotational speed */
+		__be16 pcylcount;  /* Physical cylinder count */
+		__be16 sparecyl;   /* extra sects per cylinder */
+		__be16 obs1;       /* gap1 */
+		__be16 obs2;       /* gap2 */
+		__be16 ilfact;     /* Interleave factor */
+		__be16 ncyl;       /* Data cylinder count */
+		__be16 nacyl;      /* Alt. cylinder count */
+		__be16 ntrks;      /* Tracks per cylinder */
+		__be16 nsect;      /* Sectors per track */
+		__be16 obs3;       /* bhead - Label head offset */
+		__be16 obs4;       /* ppart - Physical Partition */
+		struct sun_partition {
+			__be32 start_cylinder;
+			__be32 num_sectors;
+		} partitions[8];
+		__be16 magic;      /* Magic number */
+		__be16 csum;       /* Label xor'd checksum */
+	} * label;
+	struct sun_partition *p;
+	unsigned long spc;
+	int use_vtoc;
+	int nparts;
+
+	label = read_part_sector(state, 0, &sect);
+	if (!label)
+		return -1;
+
+	p = label->partitions;
+	if (be16_to_cpu(label->magic) != SUN_LABEL_MAGIC) {
+		put_dev_sector(sect);
+		return 0;
+	}
+	/* Look at the checksum */
+	ush = ((__be16 *) (label+1)) - 1;
+	for (csum = 0; ush >= ((__be16 *) label);)
+		csum ^= *ush--;
+	if (csum) {
+		printk("Dev %s Sun disklabel: Csum bad, label corrupted\n",
+		       state->disk->disk_name);
+		put_dev_sector(sect);
+		return 0;
+	}
+
+	/* Check to see if we can use the VTOC table */
+	use_vtoc = ((be32_to_cpu(label->vtoc.sanity) == SUN_VTOC_SANITY) &&
+		    (be32_to_cpu(label->vtoc.version) == 1) &&
+		    (be16_to_cpu(label->vtoc.nparts) <= 8));
+
+	/* Use 8 partition entries if not specified in validated VTOC */
+	nparts = (use_vtoc) ? be16_to_cpu(label->vtoc.nparts) : 8;
+
+	/*
+	 * So that old Linux-Sun partitions continue to work,
+	 * alow the VTOC to be used under the additional condition ...
+	 */
+	use_vtoc = use_vtoc || !(label->vtoc.sanity ||
+				 label->vtoc.version || label->vtoc.nparts);
+	spc = be16_to_cpu(label->ntrks) * be16_to_cpu(label->nsect);
+	for (i = 0; i < nparts; i++, p++) {
+		unsigned long st_sector;
+		unsigned int num_sectors;
+
+		st_sector = be32_to_cpu(p->start_cylinder) * spc;
+		num_sectors = be32_to_cpu(p->num_sectors);
+		if (num_sectors) {
+			put_partition(state, slot, st_sector, num_sectors);
+			state->parts[slot].flags = 0;
+			if (use_vtoc) {
+				if (be16_to_cpu(label->vtoc.infos[i].id) == LINUX_RAID_PARTITION)
+					state->parts[slot].flags |= ADDPART_FLAG_RAID;
+				else if (be16_to_cpu(label->vtoc.infos[i].id) == SUN_WHOLE_DISK)
+					state->parts[slot].flags |= ADDPART_FLAG_WHOLEDISK;
+			}
+		}
+		slot++;
+	}
+	seq_buf_puts(&state->pp_buf, "\n");
+	put_dev_sector(sect);
+	return 1;
+}