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, 92 insertions, 0 deletions

diff --git a/block/partitions/sysv68.c b/block/partitions/sysv68.c
new file mode 100644
index 000000000..470e0f9de
--- /dev/null
+++ b/block/partitions/sysv68.c
@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  fs/partitions/sysv68.c
+ *
+ *  Copyright (C) 2007 Philippe De Muyter <phdm@macqel.be>
+ */
+
+#include "check.h"
+
+/*
+ *	Volume ID structure: on first 256-bytes sector of disk
+ */
+
+struct volumeid {
+	u8	vid_unused[248];
+	u8	vid_mac[8];	/* ASCII string "MOTOROLA" */
+};
+
+/*
+ *	config block: second 256-bytes sector on disk
+ */
+
+struct dkconfig {
+	u8	ios_unused0[128];
+	__be32	ios_slcblk;	/* Slice table block number */
+	__be16	ios_slccnt;	/* Number of entries in slice table */
+	u8	ios_unused1[122];
+};
+
+/*
+ *	combined volumeid and dkconfig block
+ */
+
+struct dkblk0 {
+	struct volumeid dk_vid;
+	struct dkconfig dk_ios;
+};
+
+/*
+ *	Slice Table Structure
+ */
+
+struct slice {
+	__be32	nblocks;		/* slice size (in blocks) */
+	__be32	blkoff;			/* block offset of slice */
+};
+
+
+int sysv68_partition(struct parsed_partitions *state)
+{
+	int i, slices;
+	int slot = 1;
+	Sector sect;
+	unsigned char *data;
+	struct dkblk0 *b;
+	struct slice *slice;
+
+	data = read_part_sector(state, 0, &sect);
+	if (!data)
+		return -1;
+
+	b = (struct dkblk0 *)data;
+	if (memcmp(b->dk_vid.vid_mac, "MOTOROLA", sizeof(b->dk_vid.vid_mac))) {
+		put_dev_sector(sect);
+		return 0;
+	}
+	slices = be16_to_cpu(b->dk_ios.ios_slccnt);
+	i = be32_to_cpu(b->dk_ios.ios_slcblk);
+	put_dev_sector(sect);
+
+	data = read_part_sector(state, i, &sect);
+	if (!data)
+		return -1;
+
+	slices -= 1; /* last slice is the whole disk */
+	seq_buf_printf(&state->pp_buf, "sysV68: %s(s%u)", state->name, slices);
+	slice = (struct slice *)data;
+	for (i = 0; i < slices; i++, slice++) {
+		if (slot == state->limit)
+			break;
+		if (be32_to_cpu(slice->nblocks)) {
+			put_partition(state, slot,
+				be32_to_cpu(slice->blkoff),
+				be32_to_cpu(slice->nblocks));
+			seq_buf_printf(&state->pp_buf, "(s%u)", i);
+		}
+		slot++;
+	}
+	seq_buf_puts(&state->pp_buf, "\n");
+	put_dev_sector(sect);
+	return 1;
+}