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, 111 insertions, 0 deletions

diff --git a/block/partitions/of.c b/block/partitions/of.c
new file mode 100644
index 000000000..53664ea06
--- /dev/null
+++ b/block/partitions/of.c
@@ -0,0 +1,111 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/blkdev.h>
+#include <linux/major.h>
+#include <linux/of.h>
+#include <linux/string.h>
+#include "check.h"
+
+static int validate_of_partition(struct device_node *np, int slot)
+{
+	u64 offset, size;
+	int len;
+
+	const __be32 *reg = of_get_property(np, "reg", &len);
+	int a_cells = of_n_addr_cells(np);
+	int s_cells = of_n_size_cells(np);
+
+	/* Make sure reg len match the expected addr and size cells */
+	if (len / sizeof(*reg) != a_cells + s_cells)
+		return -EINVAL;
+
+	/* Validate offset conversion from bytes to sectors */
+	offset = of_read_number(reg, a_cells);
+	if (offset % SECTOR_SIZE)
+		return -EINVAL;
+
+	/* Validate size conversion from bytes to sectors */
+	size = of_read_number(reg + a_cells, s_cells);
+	if (!size || size % SECTOR_SIZE)
+		return -EINVAL;
+
+	return 0;
+}
+
+static void add_of_partition(struct parsed_partitions *state, int slot,
+			     struct device_node *np)
+{
+	struct partition_meta_info *info;
+	const char *partname;
+	int len;
+
+	const __be32 *reg = of_get_property(np, "reg", &len);
+	int a_cells = of_n_addr_cells(np);
+	int s_cells = of_n_size_cells(np);
+
+	/* Convert bytes to sector size */
+	u64 offset = of_read_number(reg, a_cells) / SECTOR_SIZE;
+	u64 size = of_read_number(reg + a_cells, s_cells) / SECTOR_SIZE;
+
+	put_partition(state, slot, offset, size);
+
+	if (of_property_read_bool(np, "read-only"))
+		state->parts[slot].flags |= ADDPART_FLAG_READONLY;
+
+	/*
+	 * Follow MTD label logic, search for label property,
+	 * fallback to node name if not found.
+	 */
+	info = &state->parts[slot].info;
+	partname = of_get_property(np, "label", &len);
+	if (!partname)
+		partname = of_get_property(np, "name", &len);
+	strscpy(info->volname, partname, sizeof(info->volname));
+
+	seq_buf_printf(&state->pp_buf, "(%s)", info->volname);
+}
+
+int of_partition(struct parsed_partitions *state)
+{
+	struct device *ddev = disk_to_dev(state->disk);
+	struct device_node *np;
+	int slot;
+
+	struct device_node *partitions_np = of_node_get(ddev->of_node);
+
+	if (!partitions_np ||
+	    !of_device_is_compatible(partitions_np, "fixed-partitions")) {
+		of_node_put(partitions_np);
+		return 0;
+	}
+
+	slot = 1;
+	/* Validate parition offset and size */
+	for_each_child_of_node(partitions_np, np) {
+		if (validate_of_partition(np, slot)) {
+			of_node_put(np);
+			of_node_put(partitions_np);
+
+			return -1;
+		}
+
+		slot++;
+	}
+
+	slot = 1;
+	for_each_child_of_node(partitions_np, np) {
+		if (slot >= state->limit) {
+			of_node_put(np);
+			break;
+		}
+
+		add_of_partition(state, slot, np);
+
+		slot++;
+	}
+
+	seq_buf_puts(&state->pp_buf, "\n");
+
+	of_node_put(partitions_np);
+	return 1;
+}