Beginning to describe EFI isohybrid with Apple partition map and GPT.
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@ -17,7 +17,8 @@ EL Torito CD booting, for PC-BIOS x86, PowerPC, (old) Mac, EFI.
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MBR, for PC-BIOS x86 from (pseudo-) hard disk
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- SYSLINUX isohybrid MBR
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- GRUB2 grub-mkrescue MBR.
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>>> under construction: - SYSLINUX isohybrid for UEFI and x86 Mac
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- GRUB2 grub-mkrescue MBR
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MIPS Volume Header, for MIPS Big Endian, e.g. SGI Indigo2.
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@ -394,6 +395,257 @@ hpa about MBR templates and partition table filesystem types:
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IFS Hidden") seems safeish, some people believe 0x83 (Linux) is better.
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"
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>>> SYSLINUX isohybrid for UEFI and x86-Mac
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Sources:
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http://mjg59.dreamwidth.org/11285.html
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http://mjg59.fedorapeople.org/Fedora-LiveCD.iso
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http://opensource.apple.com/source/IOStorageFamily/IOStorageFamily-116/IOApplePartitionScheme.h (typedef struct Block0)
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http://www.informit.com/articles/article.aspx?p=376123&seqNum=3
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http://en.wikipedia.org/wiki/GUID_Partition_Table
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syslinux-4.05/utils/isohybrid.c
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>>> Motivation: What systems will use the additional data ? amd64 UEFI ?
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Newer SYSLINUX MBR templates begin by 32 bytes of machine code which are
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intentionally non-essential:
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33 ed 90 90 90 90 90 90 90 90 90 90 90 90 90 90
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90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
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They may be overwritten by other bytes which must not produce errors or
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undesirable side effects when executed as x86 machine code.
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The following 32 bytes from block 0 of an Apple Partiton Map (APM) are such
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harmless code. They stem from Fedora-LiveCD.iso by Matthew Garret:
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45 52 08 00 00 00 90 90 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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The layout of a Block0 of an APM is:
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Byte Range | Value | Meaning (all numbers are stored big endian)
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---------- | ---------- | ----------------------------------------------------
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0 - 1 | sig | Signature 0x45 = 'E' , 0x52 = 'R'
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2 - 3 | block_size | 0x0800 = 2048
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4 - 7 | block_count| 0x9090 = 37008
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8 - 9 | dev_type | obscure: "device type"
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10 - 11 | dev_id | obscure: "device id"
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12 - 15 | drv_data | obscure: "driver data"
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16 - 17 | drv_count | obscure: "driver descriptor count"
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18 - 81 | drv_map | obscure: "driver descriptor table"
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| | with 8 entries of 16 bytes each
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82 - 511 | reserved |
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---------- | ---------- | ----------------------------------------------------
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(The block_count of 0x9090 is pure fantasy. It shall only mark the disc as
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not empty.)
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For the purpose of booting, there may be two EFI boot image files in the
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ISO image. A VFAT image and a HFS+ image. The content of both is not in the
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scope of this document.
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These boot images get announced by EL Torito boot catalog entries with
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Platform Id 0xef.
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The data block ranges of the two EFI boot images get described by MBR
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partition entries 2 and 3, which thus claim blocks inside of partition 1.
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This partition nesting is acceptable to some EFI implementations only if the
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type of partition 1 is 0x00.
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The second 512-block in the ISO image is a GPT header.
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45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00
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E F I P A R T
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13 db 71 5d 00 00 00 00 01 00 00 00 00 00 00 00
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fe 4f 14 00 00 00 00 00 30 00 00 00 00 00 00 00
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de 4f 14 00 00 00 00 00 73 23 c8 79 19 e6 97 4d
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95 17 69 30 c5 38 e2 99 10 00 00 00 00 00 00 00
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80 00 00 00 80 00 00 00 5b 6b 8a 65
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Byte Range | Value | Meaning (little endian numbers, LBA unit is 512 byte)
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---------- | ---------- | ----------------------------------------------------
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0 - 7 | sig | Signature "EFI PART" (with no trailing zero)
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8 - 11 | revision | Revision = {0x00, 0x00, 0x01, 0x00} meaning "1.0"
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12 - 15 | head_size | Header size = 0x5c = 92
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16 - 19 | head_crc | CRC-32 of this header while head_crc is 0
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20 - 23 | reserved | = 0
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24 - 31 | curr_lba | Location of this header block = 0x1
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32 - 39 | back_lba | Location of header backup block = 0x144ffe = 1331198
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>>> ??? That is 437.5 2K-blocks after the image end
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>>> ??? which is at 332362 (* 4 = 1329448)
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>>> ??? 1 MiB alignment ?
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40 - 47 | first_lba | First usable LBA for partitions = 0x30 = 48
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48 - 55 | last_lba | Last usable LBA for partitions = 0x144fde = 1331166
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56 - 71 | guid | Disk GUID / UUID = {
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| | 0x73, 0x23, 0xc8, 0x79, 0x19, 0xe6, 0x97, 0x4d,
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| | 0x95, 0x17, 0x69, 0x30, 0xc5, 0x38, 0xe2, 0x99 }
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72 - 79 | part_start | Partition entries start LBA = 0x10 = 16 = byte 0x2000
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| | (This is unusual. It leaves room for the Apple
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| | partition map entries.)
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80 - 83 | entry_count| Number of partition entries = 0x80 = 128
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84 - 87 | entry_size | Size of a partition entry = 0x80 = 128
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88 - 91 | p_arr_crc | CRC-32 of the partition array
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92 - 511 | reserved | Must be 0
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---------- | ---------- | ----------------------------------------------------
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>>> CRC-32: Generating polynomial 0x104c11db7, mirrored bit order in and out,
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>>> seed 0xffffffff, result gets exored by 0xffffffff.
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>>> ??? This works as byte shifter with a bitwise mirrored table
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>>> ??? but not as simple bit shifter.
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>>> ??? Both do match if seed == 0. But not with other seeds.
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>>> ??? An algebraic miracle ?
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The ISO image has a size of 332362 blocks of 2K = 1329448 blocks of 512.
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Because the block size was announced as 2048, the first Apple partition map
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entry is located at byte 0x800.
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It describes the partition map itself:
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50 4d 00 00 00 00 00 03 00 00 00 01 00 00 00 10
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P M
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41 70 70 6c 65 00 00 00 00 00 00 00 00 00 00 00
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A p p l e
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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41 70 70 6c 65 5f 70 61 72 74 69 74 69 6f 6e 5f
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A p p l e _ p a r t i t i o n _
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6d 61 70 00 00 00 00 00 00 00 00 00 00 00 00 00
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m a p
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00 00 00 00 00 00 00 0a 00 00 00 03 00 00 00 00
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The layout of an Apple partition map entry is:
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Byte Range | Value | Meaning (all numbers are stored big endian)
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---------- | ---------- | ----------------------------------------------------
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0 - 1 | sig | Signature 0x50 = 'P' , 0x4d = 'M'
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2 - 3 | reserved |
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4 - 7 | map_entries| "number of partition entries" = 3
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8 - 11 | start_block| "physical block start of partition" = 1
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12 - 15 | block_count| "physical block count of partition" = 16
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| | (The value of 16 claims the ISO 9660 PVD as part of
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| | the partition table. This might be unhealthy.)
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16 - 47 | name | Partition name = "Apple"
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48 - 79 | type | Type string = "Apple_partition_map"
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80 - 83 | lb_start | Logical block start = 0
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84 - 87 | lb_count | Logical block count = 10
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88 - 91 | flags | Status flags = 3
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| | bit0= entry is valid
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| | bit1= entry is allocated
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| | bit4= partition is readable
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| | bit5= partition is writable
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92 - 95 | boot_block | Logical start block number of boot code = 0
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96 - 99 | boot_bytes | Number of bytes in boot code = 0
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100 - 119 | | More boot code stuff = 0
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120 - 135 | processor | "processor type" = 0
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136 - 511 | reserved |
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---------- | ---------- | ----------------------------------------------------
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The next Apple partition map entry is at byte 0x1000:
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50 4d 00 00 00 00 00 03 00 00 00 29 00 00 04 70
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45 46 49 00 00 00 00 00 00 00 00 00 00 00 00 00
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E F I
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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41 70 70 6c 65 5f 48 46 53 00 00 00 00 00 00 00
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A p p l e _ H F S
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 04 70 00 00 00 33 00 00 00 00
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3 partitions, start block is 0x29 = 41, block count is 0x0470 = 1136,
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name is "EFI", type is "Apple_HFS"
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>>> although this is a FAT image
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, logical block start = 0, lb_count = 1136,
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flags = 0x33 : valid, allocated, readable, writable.
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This points to file /isolinux/efiboot.img in the ISO image,
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>>> but misrepresents its size of 284 blocks of 2048.
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At byte 0x1800, there is map entry 3:
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50 4d 00 00 00 00 00 03 00 00 01 51 00 00 08 c0
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45 46 49 00 00 00 00 00 00 00 00 00 00 00 00 00
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E F I
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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41 70 70 6c 65 5f 48 46 53 00 00 00 00 00 00 00
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A p p l e _ H F S
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 08 c0 00 00 00 33 00 00 00 00
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3 partitions, start block is 0x0151 = 337 (LBA of /isolinux/macboot.img),
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block count = 2240
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>>> (4 times higher than ISO size of 560 blocks)
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, name is "EFI", type is "Apple_HFS",
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, logical block start = 0, lb_count = 2240,
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flags = 0x33 : valid, allocated, readable, writable.
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>>> GPT partitions marking ISO image, VFAT image within, HFS+ image within
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At byte 0x2000 begins the GPT partition array. It ends at byte 0x4000.
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a2 a0 d0 eb e5 b9 33 44 87 c0 68 b6 b7 26 99 c7
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a1 87 a1 ba 4d 2c 27 45 ae 05 cf ab a6 fa 87 c1
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00 00 00 00 00 00 00 00 28 49 14 00 00 00 00 00
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00 00 00 00 00 00 00 00 49 53 4f 48 79 62 72 69
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I S O H y b r i
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64 20 49 53 4f 00 49 53 4f 48 79 62 72 69 64 00
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d I S O I S O H y b r i d
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41 70 70 6c 00 00 00 00 00 00 00 00 00 00 00 00
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A p p l
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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A GPT partion entry looks like:
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Byte Range | Value | Meaning (numbers are stored little endian)
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---------- | ---------- | ----------------------------------------------------
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0 - 15 | type_guid | Partition type guid = random
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16 - 31 | part_guid | Unique partition GUID = random
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32 - 39 | start_lba | First LBA = 0
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40 - 47 | end_lba | Last LBA (inclusive) = 0x144828 = 1329448
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| | This is the ISO image size in blocks of 512.
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>>> But it should be 1 block less than that
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48 - 55 | flags | Attribute flags
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| | bit0= "System Partition" Do not alter.
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| | bit2= Legacy BIOS bootable (MBR partition type 0x80)
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| | bit60= read-only
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56 - 127 | name | >>> Wikipedia says UTF-16LE.
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| | >>> The name in Fedora-LiveCD.iso is 8 bit and result
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| | >>> of faulty memory operation on a text constant.
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---------- | ---------- | ----------------------------------------------------
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Next entry:
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a2 a0 d0 eb e5 b9 33 44 87 c0 68 b6 b7 26 99 c7
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c8 de c8 1f fb f0 51 40 8c 8a d2 f6 b1 46 16 dc
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a4 00 00 00 00 00 00 00 13 05 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 49 53 4f 48 79 62 72 69
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I S O H y b r i
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64 00 41 70 70 6c 65 00 41 70 70 6c 00 00 00 00
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d A p p l e A p p l
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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Start at block 0xa4 = 164 * 512 = 41 * 2048. The VFAT image file.
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Last block is 0x0513 = 1299 = 164 + 1135. This end is correct.
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>>> The name is an unintentional patchwork in an 8 bit character set.
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Next entry:
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00 53 46 48 00 00 aa 11 aa 11 00 30 65 43 ec ac
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c8 de c8 1f fb f0 51 40 8c 8a d2 f6 b1 46 16 dc
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44 05 00 00 00 00 00 00 03 0e 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 49 53 4f 48 79 62 72 69
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I S O H y b r i
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64 00 41 70 70 6c 65 00 41 70 70 6c 00 00 00 00
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d A p p l e A p p l
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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Start block is 0x0544 = 1348 * 512 = 337 * 2048. The HFS+ image file.
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Last block is 0x0e03 = 3587 = 1348 + 2239. Correct.
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>>> Frankenstein's name, again.
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The rest of the System Area is 0 up to the Primary Volume Descriptor
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at block 16.
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------------------------------------------------------------------------------
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