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, 68 insertions, 0 deletions

diff --git a/block/partitions/check.h b/block/partitions/check.h
new file mode 100644
index 000000000..b0997467b
--- /dev/null
+++ b/block/partitions/check.h
@@ -0,0 +1,68 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/pagemap.h>
+#include <linux/blkdev.h>
+#include <linux/seq_buf.h>
+#include "../blk.h"
+
+/*
+ * add_gd_partition adds a partitions details to the devices partition
+ * description.
+ */
+struct parsed_partitions {
+	struct gendisk *disk;
+	char name[BDEVNAME_SIZE];
+	struct {
+		sector_t from;
+		sector_t size;
+		int flags;
+		bool has_info;
+		struct partition_meta_info info;
+	} *parts;
+	int next;
+	int limit;
+	bool access_beyond_eod;
+	struct seq_buf pp_buf;
+};
+
+typedef struct {
+	struct folio *v;
+} Sector;
+
+void *read_part_sector(struct parsed_partitions *state, sector_t n, Sector *p);
+static inline void put_dev_sector(Sector p)
+{
+	folio_put(p.v);
+}
+
+static inline void
+put_partition(struct parsed_partitions *p, int n, sector_t from, sector_t size)
+{
+	if (n < p->limit) {
+		p->parts[n].from = from;
+		p->parts[n].size = size;
+		seq_buf_printf(&p->pp_buf, " %s%d", p->name, n);
+	}
+}
+
+/* detection routines go here in alphabetical order: */
+int adfspart_check_ADFS(struct parsed_partitions *state);
+int adfspart_check_CUMANA(struct parsed_partitions *state);
+int adfspart_check_EESOX(struct parsed_partitions *state);
+int adfspart_check_ICS(struct parsed_partitions *state);
+int adfspart_check_POWERTEC(struct parsed_partitions *state);
+int aix_partition(struct parsed_partitions *state);
+int amiga_partition(struct parsed_partitions *state);
+int atari_partition(struct parsed_partitions *state);
+int cmdline_partition(struct parsed_partitions *state);
+int efi_partition(struct parsed_partitions *state);
+int ibm_partition(struct parsed_partitions *);
+int karma_partition(struct parsed_partitions *state);
+int ldm_partition(struct parsed_partitions *state);
+int mac_partition(struct parsed_partitions *state);
+int msdos_partition(struct parsed_partitions *state);
+int of_partition(struct parsed_partitions *state);
+int osf_partition(struct parsed_partitions *state);
+int sgi_partition(struct parsed_partitions *state);
+int sun_partition(struct parsed_partitions *state);
+int sysv68_partition(struct parsed_partitions *state);
+int ultrix_partition(struct parsed_partitions *state);