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, 115 insertions, 0 deletions

diff --git a/block/partitions/efi.h b/block/partitions/efi.h
new file mode 100644
index 000000000..84b9f36b9
--- /dev/null
+++ b/block/partitions/efi.h
@@ -0,0 +1,115 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/************************************************************
+ * EFI GUID Partition Table
+ * Per Intel EFI Specification v1.02
+ * http://developer.intel.com/technology/efi/efi.htm
+ *
+ * By Matt Domsch <Matt_Domsch@dell.com>  Fri Sep 22 22:15:56 CDT 2000  
+ *   Copyright 2000,2001 Dell Inc.
+ ************************************************************/
+
+#ifndef FS_PART_EFI_H_INCLUDED
+#define FS_PART_EFI_H_INCLUDED
+
+#include <linux/types.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/major.h>
+#include <linux/string.h>
+#include <linux/efi.h>
+#include <linux/compiler.h>
+
+#define MSDOS_MBR_SIGNATURE 0xaa55
+#define EFI_PMBR_OSTYPE_EFI 0xEF
+#define EFI_PMBR_OSTYPE_EFI_GPT 0xEE
+
+#define GPT_MBR_PROTECTIVE  1
+#define GPT_MBR_HYBRID      2
+
+#define GPT_HEADER_SIGNATURE 0x5452415020494645ULL
+#define GPT_HEADER_REVISION_V1 0x00010000
+#define GPT_PRIMARY_PARTITION_TABLE_LBA 1
+
+#define PARTITION_SYSTEM_GUID \
+    EFI_GUID( 0xC12A7328, 0xF81F, 0x11d2, \
+              0xBA, 0x4B, 0x00, 0xA0, 0xC9, 0x3E, 0xC9, 0x3B) 
+#define LEGACY_MBR_PARTITION_GUID \
+    EFI_GUID( 0x024DEE41, 0x33E7, 0x11d3, \
+              0x9D, 0x69, 0x00, 0x08, 0xC7, 0x81, 0xF3, 0x9F)
+#define PARTITION_MSFT_RESERVED_GUID \
+    EFI_GUID( 0xE3C9E316, 0x0B5C, 0x4DB8, \
+              0x81, 0x7D, 0xF9, 0x2D, 0xF0, 0x02, 0x15, 0xAE)
+#define PARTITION_BASIC_DATA_GUID \
+    EFI_GUID( 0xEBD0A0A2, 0xB9E5, 0x4433, \
+              0x87, 0xC0, 0x68, 0xB6, 0xB7, 0x26, 0x99, 0xC7)
+#define PARTITION_LINUX_RAID_GUID \
+    EFI_GUID( 0xa19d880f, 0x05fc, 0x4d3b, \
+              0xa0, 0x06, 0x74, 0x3f, 0x0f, 0x84, 0x91, 0x1e)
+#define PARTITION_LINUX_SWAP_GUID \
+    EFI_GUID( 0x0657fd6d, 0xa4ab, 0x43c4, \
+              0x84, 0xe5, 0x09, 0x33, 0xc8, 0x4b, 0x4f, 0x4f)
+#define PARTITION_LINUX_LVM_GUID \
+    EFI_GUID( 0xe6d6d379, 0xf507, 0x44c2, \
+              0xa2, 0x3c, 0x23, 0x8f, 0x2a, 0x3d, 0xf9, 0x28)
+
+typedef struct _gpt_header {
+	__le64 signature;
+	__le32 revision;
+	__le32 header_size;
+	__le32 header_crc32;
+	__le32 reserved1;
+	__le64 my_lba;
+	__le64 alternate_lba;
+	__le64 first_usable_lba;
+	__le64 last_usable_lba;
+	efi_guid_t disk_guid;
+	__le64 partition_entry_lba;
+	__le32 num_partition_entries;
+	__le32 sizeof_partition_entry;
+	__le32 partition_entry_array_crc32;
+
+	/* The rest of the logical block is reserved by UEFI and must be zero.
+	 * EFI standard handles this by:
+	 *
+	 * uint8_t		reserved2[ BlockSize - 92 ];
+	 */
+} __packed gpt_header;
+
+typedef struct _gpt_entry_attributes {
+	u64 required_to_function:1;
+	u64 reserved:47;
+        u64 type_guid_specific:16;
+} __packed gpt_entry_attributes;
+
+typedef struct _gpt_entry {
+	efi_guid_t partition_type_guid;
+	efi_guid_t unique_partition_guid;
+	__le64 starting_lba;
+	__le64 ending_lba;
+	gpt_entry_attributes attributes;
+	__le16 partition_name[72/sizeof(__le16)];
+} __packed gpt_entry;
+
+typedef struct _gpt_mbr_record {
+	u8	boot_indicator; /* unused by EFI, set to 0x80 for bootable */
+	u8	start_head;     /* unused by EFI, pt start in CHS */
+	u8	start_sector;   /* unused by EFI, pt start in CHS */
+	u8	start_track;
+	u8	os_type;        /* EFI and legacy non-EFI OS types */
+	u8	end_head;       /* unused by EFI, pt end in CHS */
+	u8	end_sector;     /* unused by EFI, pt end in CHS */
+	u8	end_track;      /* unused by EFI, pt end in CHS */
+	__le32	starting_lba;   /* used by EFI - start addr of the on disk pt */
+	__le32	size_in_lba;    /* used by EFI - size of pt in LBA */
+} __packed gpt_mbr_record;
+
+
+typedef struct _legacy_mbr {
+	u8 boot_code[440];
+	__le32 unique_mbr_signature;
+	__le16 unknown;
+	gpt_mbr_record partition_record[4];
+	__le16 signature;
+} __packed legacy_mbr;
+
+#endif