1710 lines
77 KiB
Plaintext
1710 lines
77 KiB
Plaintext
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Collection of Boot Sector Formats for ISO 9660 Images
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by Thomas Schmitt - scdbackup@gmx.net
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Libburnia project - bug-xorriso@gnu.org
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pkg-libburnia-devel@lists.alioth.debian.org
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This information is collected from various sources. Some is backed by
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specifications, some is just rumor which happens to work (maybe not even that).
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Content
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EL Torito CD booting, for PC-BIOS x86, PowerPC, (old) Mac, EFI.
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Boot Info Table and GRUB2 Boot Info
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Master Boot Record (MBR), for PC-BIOS x86 from (pseudo-) hard disk
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Apple Partition Map (APM), for more modern Mac
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GUID Partition Table (GPT), for EFI from (pseudo-) hard disk
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MIPS Volume Header, for MIPS Big Endian, e.g. SGI Indigo2.
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DEC Boot Block, for MIPS Little Endian , e.g. DECstation.
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SUN Disk Label and boot images, for SUN SPARC
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GRUB2 SUN SPARC Core File Address
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PowerPC Reference Platform (PReP), for IBM PowerPC
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Common Hardware Reference Platform (CHRP), for IBM PowerPC
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HP-PA via PALO header version 4
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HP-PA via PALO header version 5
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DEC Alpha SRM boot sector, for Alpha architecture
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Combinations of boot mechanisms:
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- SYSLINUX isohybrid MBR
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- SYSLINUX isohybrid for MBR, UEFI and x86-Mac
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- GRUB2 grub-mkrescue MBR
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>>> Mac and/or PowerPC bootable GRUB2 image with HFS+/FAT, APM,
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EFI GPT partition, PreP MBR partition, mountable FAT partition
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------------------------------------------------------------------------------
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EL Torito CD booting
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for PC-BIOS x86, PowerPC, (old) Mac, EFI
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Sources:
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El Torito, Bootable CD-ROM Format Specification, Version 1.0, 1995
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which refers to ECMA-119, the standard for ISO 9660 filesystems.
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libisofs/eltorito.[ch] by Vreixo Formoso.
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http://www.uefi.org/sites/default/files/resources/2_4_Errata_B.pdf
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ECMA-119 prescribes that the first 32 kB of an ISO 9660 image are System Area
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with arbitrary content. This prescription is obeyed by PC-BIOS systems only
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if the ISO 9660 image is presented on CD, DVD or BD media.
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In this case the El Torito Boot record is the starting point of booting.
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After the System Area, an ISO 9660 image usually has three distinct block
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intervals for:
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- Volume descriptors (Primary Volume Descriptor, Boot Record, Joliet, ...)
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- Directory trees, tables, boot catalog, embedded partitions and filesystems.
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- Data file content, including content of El Torito boot images.
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The Boot Record is an ECMA-119 Volume Descriptor which is located at 2 kB block
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number 17 (decimal), if present at all. Its content points to the location of
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the Boot Catalog.
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The format is described in part by ECMA-119 8.2 "Boot Record" and further
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specified by El Torito figure 7.
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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0 - 0 | 0 | Volume Descriptor Type. 0= Boot record
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1 - 5 | "CD001" | Standard Identifier
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6 - 6 | 1 | Volume Descriptor Version
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7 - 38 | el_torito | Boot System Identifier
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39 - 70 | 0 | Boot Identifier
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71 -2047 | ========== | Boot System Use
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71 - 74 | cataloglba | The 2 kB block number of the Boot Catalog
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| | as little-endian 32 bit number.
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75 -2047 | 0 | Unused
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---------- | ---------- | ----------------------------------------------------
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el_torito is the constant string "EL TORITO SPECIFICATION" padded by 9 zeros.
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cataloglba has to be provided by the file system generator.
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The Boot Catalog lists the available boot images which may be prepared for
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multiple system architectures, called "platforms".
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It consists of one or more 2 kB blocks. The content is a sequence of fixed
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format entries, 32 bytes each.
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The entries are grouped in sections, which assign the entries to a particular
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system architecture. The booting system will then choose an entry from an
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appropriate section.
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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0 - 31 | ========== | Validation Entry
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| | begins the first section, specifies an architecture
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32 - 63 | ========== | Initial/Default Entry
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| | points to a boot image for given architecture
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---------- | ---------- | ----------------------------------------------------
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Optional:
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---------- | ---------- | ----------------------------------------------------
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64 - 95 | ========== | Section Header entry
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| | begins new section, specifies an architecture
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96 - 127 | ========== | Section Entry
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| | points to a boot image for given architecture
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... | .......... | Optional more Section Entries
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... | .......... | Optional more Section Headers and their Section
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| | Entries
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---------- | ---------- | ----------------------------------------------------
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An architecture is referred by a Platform Id number.
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Defined by El Torito are:
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0 = "80x86" which is used for standard PCs with Intel x86 or compatible CPU
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1 = "PowerPC" (possibly for IBM machines with PowerPC CPU)
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2 = "Mac" (possibly for Apple computers with MC68000 or PowerPC CPU)
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UEFI 2.4 specifies in 12.3.2.1 "ISO-9660 and El Torito":
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0xef = EFI, a competitor and successor to PC-BIOS, further in use with
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Intel ia64 Itanium and newer Apple machines.
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Words and numbers are represented as little-endian.
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Validation Entry:
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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0 - 0 | 1 | Header Id
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1 - 1 | platform_id| Platform Id. One of: 0, 1, 2, 0xef. See above.
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2 - 3 | 0 | Reserved
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4 - 27 | manuf_dev | ID string identifies the manufacturer/developer
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| | (no non-zero examples known yet)
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28 - 29 | checksum | Checksum Word for the Validation Entry.
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| | The sum of all words in the entry has to be 0.
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30 - 30 | 0x55 |
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31 - 31 | 0xaa |
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---------- | ---------- | ----------------------------------------------------
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Initial/Default Entry:
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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0 - 0 | boot_indct | Boot Indicator: 0x88 = bootable, 0x00 = not bootable
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1 - 1 | boot_media | Boot Media Type (i.e. media emulated by boot image):
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| | 0= no emulation , 1= 1.2 MB diskette, 2=1.44 MB,
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| | 3= 2.88 MB , 4= hard disk
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| | (About everybody uses 0 = no emulation)
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2 - 3 | load_seg | Load Segment. (meaning unclear)
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| | "If this value is 0 the system will use the
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| | traditional segment of 7C0."
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| | libisofs default is 0
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4 - 4 | sys_type | System Type.
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| | "Must be a copy of byte 5 from the partition table
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| | found in the boot image."
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| | libisofs reads the start the boot image as MBR
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| | if boot_media == 4. This emulated MBR has a
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| | partition table from where a byte gets copied.
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| | Else this byte is 0.
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5 - 5 | 0 | Unused
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6 - 7 | sec_count | Sector Count. Sector size 512:
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| | "the number of virtual/emulated sectors the system
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| | will store at Load Segment during the initial boot
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| | procedure."
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| | libisofs stores 1 for emulated boot_media and a
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| | user defined value for boot_media == 0. Often: 4.
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8 - 11 | load_rba | Load RBA. The 2 kB block address where the boot
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| | image file content is located in the ISO 9660 image.
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12 - 31 | 0 | Unused
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---------- | ---------- | ----------------------------------------------------
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Section Header Entry:
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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0 - 0 | head_ind | Header Indicator: 0x90 = more headers follow
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| | 0x91 = final header, last section
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1 - 1 | platform_id| Platform Id. One of: 0, 1, 2, 0xef. See above.
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2 - 3 | num_entries| Number of entries to follow in this section
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4 - 31 | | ID string identifies the manufacturer/developer
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---------- | ---------- | ----------------------------------------------------
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Section Entry:
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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0 - 0 | boot_indct | Boot Indicator: 0x88 = bootable, 0x00 = not bootable
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1 - 1 | boot_media | Boot Media Type (i.e. media emulated by boot image):
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| | Bit 0 to 3 govern emulation
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| | 0= no emulation , 1= 1.2 MB diskette, 2=1.44 MB,
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| | 3= 2.88 MB , 4= hard disk
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| | (About everybody uses 0 = no emulation)
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| | Bit 4 is reserved and must be 0
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| | Bit 5 "Continuation entry follows" (meaning unclear)
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| | Might be the indicator for Extension Entries,
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| | which are not described here.
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| | Bit 6 "Image contains an ATAPI driver"
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| | Bit 7 "Image contains SCSI drivers"
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2 - 3 | load_seg | Load Segment. (meaning unclear)
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| | See above Initial/Default Entry
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| | libisofs default is 0.
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4 - 4 | sys_type | System Type.
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| | See above Initial/Default Entry
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| | 0 if not emulation == 4.
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5 - 5 | 0 | Unused
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6 - 7 | sec_count | Sector Count. Sector size 512.
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| | See above Initial/Default Entry
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| | libisofs stores 1 for emulated boot_media and a
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| | user defined value for boot_media == 0. Often: 4.
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8 - 11 | load_rba | Load RBA. The 2 kB block address where the boot
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| | image file content is located in the ISO 9660 image.
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12 - 31 | sel_crit | "Vendor unique selection criteria."
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---------- | ---------- | ----------------------------------------------------
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------------------------------------------------------------------------------
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Boot Info Table and GRUB2 Boot Info
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Sources:
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man mkisofs by Joerg Schilling
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Mail conversations with Vladimir Serbinenko.
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The boot image file content is mostly opaque to the ISO 9660 image generator.
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Nevertheless there is a tradition named "Boot Info Table" which prescribes
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to write information into byte fields of the boot image file content.
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Recent versions of GRUB2 expect a similar patching which has no name yet.
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For now let's call it "GRUB2 Boot Info"
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There are no general means known how a producer of ISO 9660 images could
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detect the need for Boot Info Table production.
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It rather needs a hint from the user who has to know whether the boot image
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expects a Boot Info Table.
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The Boot Info Table begins at byte 8 of the boot image content.
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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8 - 11 | pvd_lba | Block address of the Primary Volume Descriptor.
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| | This is the session start LBA + 16.
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12 - 15 | file_lba | Block address of the start of the boot image file
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| | content. Block size is 2048.
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16 - 19 | file_len | Number of bytes in boot image file content.
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20 - 23 | checksum | The sum of all 32-bit words of the file content
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| | from byte 64 to file end.
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24 - 63 | 0 | Reserved
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---------- | ---------- | ----------------------------------------------------
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All numbers are stored little-endian.
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GRUB2 Boot Info represents a particular block address inside the boot image.
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It may well be combined with Boot Info Table. See GRUB2 script grub-mkrescue
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use of xorrisofs options -boot-info-table and --grub2-boot-info.
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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2548 -2555 | grub2_adr | Block address of the start of the boot image file
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| | content plus 5. Block size is 512.
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| | 64 bit Little-endian.
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---------- | ---------- | ----------------------------------------------------
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------------------------------------------------------------------------------
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Master Boot Record (MBR)
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for PC-BIOS x86 from (pseudo-) hard disk
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Sources:
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http://en.wikipedia.org/wiki/Master_boot_record
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https://en.wikipedia.org/wiki/INT_13H
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Mailing list conversations with H. Peter Anvin and Vladimir Serbinenko.
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Mail conversations with Natalia Portillo.
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The candidates for MBR booting will normally use El Torito rather than MBR
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if the ISO image is presented on CD, DVD, or BD media.
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The MBR comes into effect if the image is on a media that is interpreted by
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the BIOS as some kind of hard disk. Usually real hard disks, floppy disks,
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USB sticks, memory cards.
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An important part of an MBR is the DOS style partition table. It describes up
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to four primary partitions. There are two formats used for block address:
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Cylinder/Head/Sector (C/H/S) and Logical Block Address (LBA). Both are based
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on units of 512 bytes. So MBR_LBA = ISO_LBA * 4.
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Contemporary x86 BIOS normally supports LBA addressing directly.
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If INT 0x13 AH 0x41 returns with CX bit0 set, then INT 0x13 AH 0x42 may be used
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for reading. (Sometimes even if the bit is not set to indicate the capability.)
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For C/H/S, the sector address is broken up into whole cylinders, remaining
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heads, and remaining sectors + 1. The nomenclature seems to stem from antique
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drum storage.
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There are two parameters, sectors_per_head and heads_per_cylinder which are not
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stored in the MBR. So at ISO production time it is more or less arbitrary how
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to convert a LBA into a C/H/S address and vice versa.
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At boot time the x86 BIOS decides about the two parameters. The boot loader may
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inquire these values by INT 0x13 AH 0x08 and use them to convert LBA to C/H/S
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for the read operation INT 0x13 AH 0x02. So the C/H/S values in an ISO's
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partition table are quite fictional and of few impact on boot loaders.
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More important seems to align partition ends to a consistent cylinder size,
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because some partition editors deduce their idea of disk geometry from there
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and raise protest if they deem it inconsistent.
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For maximum range of C/H/S addresses one may use sectors_per_head = 63 ,
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heads_per_cylinder = 255. But that is not divisible by 4 and imposes alignment
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problems with ISO 9660 filesystems. So (32,64) for images up to 1 GiB
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or (63,252) for larger images are better.
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Words are composed little-endian style.
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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0 - 439 | = opaque = | Code Area filled with bytes for some boot system,
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| | typically machine code.
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440 - 443 | disk_sgntr | Disc signature: An individual disk id. Some software
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| | might use it to recognize the same storage medium
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| | at different device addresses.
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| | (The Code Area might extend up to this field.)
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444 - 445 | 0 | "usually nulls"
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| | (The Code Area might extend up to this field.)
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446 - 461 | ========== | Partition Table Entry for partition 1
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446 - 446 | status | For some generic MBRs this marks the one partition
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| | from which the MBR should load and run more code.
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| | 0x80 = bootflag/active , 0x00 = noboot/inactive
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| | Some BIOSes ignore MBRs with no bootflag in any of
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| | their partition table entries.
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447 - 449 | ========== | C/H/S address of partition start
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447 - 447 | start_head | Heads part of start address.
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448 - 448 | start_c_s | Bits 0 to 5 : Sectors part of start address.
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| | Bits 6 to 7 : Bits 8 to 9 of cylinders part.
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449 - 449 | start_cyl | Lower 8 bits of cylinders part of start address
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450 - 450 | part_type | Partition type indicates the purpose or kind of
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| | filesystem in the partition.
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451 - 453 | ========== | C/H/S address of last absolute sector in partition
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451 - 451 | end_head | Heads part of end address.
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452 - 452 | end_c_s | Bits 0 to 5 : Sectors part of end address.
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| Values: 1 to 63, not 0.
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| | Bits 6 to 7 : Bits 8 to 9 of cylinders part.
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453 - 453 | end_cyl | Lower 8 bits of cylinders part of end address
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454 - 457 | start_lba | LBA of first absolute sector in partition.
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| | Block size is 512. Counting starts at 0.
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458 - 461 | num_blocks | Number of sectors in partition.
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462 - 477 | ========== | Partition Table Entry for partition 2
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| part_entr2 | 16 bytes. Format as with partition 1.
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| | All 0 means that partition is unused/undefined.
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478 - 493 | ========== | Partition Table Entry for partition 3
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| part_entr3 | 16 bytes. See above.
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494 - 509 | ========== | Partition Table Entry for partition 4
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| part_entr4 | 16 bytes. See above.
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510 - 510 | 0x55 | MBR signature
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511 - 511 | 0xaa | MBR signature
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---------- | ---------- | ----------------------------------------------------
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By tradition the MBR itself and possibly more blocks are not claimed by any
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partition. But starting the first partition at a non-zero block address causes
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on Linux a partition device file (e.g. /dev/sdb1) which cannot be used to mount
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the ISO filesystem.
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libisofs is able to produce a second set of trees and meta data which is
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suitable for being mounted at start block 16 (ISO) which is block 64 in MBR.
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See <libisofs/libisofs.h> for call iso_write_opts_set_part_offset()
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and http://libburnia-project.org/wiki/PartitionOffset for examples with
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program xorriso.
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------------------------------------------------------------------------------
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Apple Partition Map (APM)
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for Apple Macs introduced since 2000 and more computer-like than iPad
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from CD and often from (pseudo-) hard disk
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Sources:
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http://mjg59.dreamwidth.org/11285.html
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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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syslinux-4.05/utils/isohybrid.c
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Mail conversations with Vladimir Serbinenko.
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Mail conversations with Natalia Portillo of DiskImageChef,
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who quoted "Inside Macintosh" Volumes IV and V.
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APM has an adjustable block size. Because the ISO images shall always work
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on optical media, and in order to make room for the header block of an
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additional GPT, only block size 2048 is considered here.
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The role of APM in the boot process is to guide the firmware to a
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HFS+ filesystem.
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Block0 (aka Driver Descriptor Map) of an APM begins at byte 0 of the medium.
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Thus it collides with MBR and other boot sector formats. By lucky coincidence
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it is possible to compose a mock-up of a Block0 which is acceptable to firmware
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which expects APM, and is also harmless x86 machine code with no negative
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side effects. So it is possible to combine APM with an especially prepared MBR.
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Block0 is optional. But in the context of bootable hybrid ISOs it is not only
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needed to announce block size 2048, but also it is much better suited for
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staging as harmless x86 machine code than is an APM partition entry.
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Usually there is no Device Partition Map block (signature "TS"), although it
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is demanded by the book "Inside Macintosh". It would sit where GPT has its
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header block. So DPM is not described here.
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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| Number of blocks covered by APM
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| | Often some x86-harmless dummy. E.g. 0x9090 = 37008
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| | or 0xeb02ffff = 3,942,842,367
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8 - 9 | dev_type | Device type: The id of the Mac driver which is in
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| | charge of the storage device.
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10 - 11 | dev_id | Device id: Address in an i/o bus system.
|
|
12 - 15 | drv_data | Driver data: Not used.
|
|
16 - 17 | drv_count | Driver count: Count of entries in drv_map.
|
|
18 - 505 | drv_map | Driver descriptor table:
|
|
| | Up to 61 entries of 8 bytes each.
|
|
| | They contain the 32 bit 512-byte LBA of the driver's
|
|
| | storage location, its 16 bit size in 512-byte blocks,
|
|
| | and value 0x0001.
|
|
506 - 511 | reserved |
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
The SYSLINUX program isohybrid.c overwrites the first 32 bytes of this
|
|
layout by its dummy values. It uses the small block_count 0x00009090 and
|
|
sets all bytes up to 31 to 0.
|
|
The libisofs HFS+ extension by Vladimir Serbinenko overwrites only the
|
|
first 8 bytes. It uses the large block_count 0xeb02ffff.
|
|
|
|
Block0 and the following APM entries each occupy 1 block of the announced size.
|
|
|
|
The first APM entry describes the range from its own start to the end of the
|
|
last APM entry. Each of the other APM entries describes a partition.
|
|
|
|
The layout of an Apple partition map entry is:
|
|
|
|
Byte Range | Value | Meaning (all numbers are stored big endian)
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 1 | sig | Signature 0x50 = 'P' , 0x4d = 'M'
|
|
2 - 3 | reserved |
|
|
4 - 7 | map_entries| Number of partition entries.
|
|
| | All entries show the same number.
|
|
8 - 11 | start_block| "physical block start of partition"
|
|
12 - 15 | block_count| "physical block count of partition"
|
|
16 - 47 | name | Partition name
|
|
48 - 79 | type | Type string
|
|
80 - 83 | lb_start | Logical block start = 0
|
|
84 - 87 | lb_count | Logical block count (same as block_count)
|
|
88 - 91 | flags | Status flags
|
|
| | bit0= entry is valid
|
|
| | bit1= partition is allocated
|
|
| | bit2= partition is in use
|
|
| | bit3= partition contains valid boot information
|
|
| | bit4= partition is readable
|
|
| | bit5= partition is writable
|
|
| | bit7= boot code is position independent
|
|
| | bit30= automatic mount (legacy Mac)
|
|
92 - 95 | boot_block | Logical start block number of boot code = 0
|
|
96 - 99 | boot_bytes | Number of bytes in boot code = 0
|
|
100 - 119 | | More boot code stuff = 0
|
|
120 - 135 | processor | "processor type" = 0
|
|
136 - 511 | reserved |
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
For the first APM entry (byte 0x0800), the following values apply:
|
|
map_entries = number of APM entries, including itself. E.g. 4.
|
|
start_block = 1
|
|
block_count = map_entries
|
|
name = "Apple"
|
|
type = "Apple_partition_map"
|
|
flags = 3
|
|
|
|
libisofs uses APM to mark a HFS+ filesystem partition within an ISO 9660 image.
|
|
Usually the APM has 3 more entries after the first entry:
|
|
|
|
Entry 2 (byte 0x1000) describes the block interval from ISO image start to
|
|
the start of the HFS+ filesystem meta data.
|
|
start_block = 16
|
|
block_count = start_of_hfs - 16
|
|
name = "Gap0"
|
|
type = "ISO9660_data"
|
|
flags = 0x13
|
|
|
|
Entry 3 (byte 0x1800) describes the interval from the start of the HFS+ meta
|
|
data to the end of the HFS+ data at the end of its partition. This includes all
|
|
content blocks of the data files in the ISO image.
|
|
start_block = start_of_hfs
|
|
block_count = end_of_hfs - start_of_hfs
|
|
name = "HFSPLUS_Hybrid"
|
|
type = "Apple_HFS"
|
|
flags = 0x40000013
|
|
|
|
Entry 4 (byte 0x2000) describes the interval from the end of the HFS+
|
|
partition to the end of the ISO image. It is possible that this interval is
|
|
empty. In this case, no fourth APM entry will be written.
|
|
start_block = end_of_hfs
|
|
block_count = end_of_iso - end_of_hfs
|
|
name = "Gap1"
|
|
type = "ISO9660_data"
|
|
flags = 0x13
|
|
|
|
|
|
>>> Open questions:
|
|
>>> What HFS+ blessings are needed for booting ?
|
|
>>> What files need what HFS creator and type settings ?
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
GUID Partition Table (GPT)
|
|
for alternative mountability paths
|
|
and for EFI booting of some Apple Macs from (pseudo-) hard disk
|
|
|
|
Sources:
|
|
http://mjg59.dreamwidth.org/11285.html
|
|
http://mjg59.fedorapeople.org/Fedora-LiveCD.iso
|
|
http://en.wikipedia.org/wiki/GUID_Partition_Table
|
|
http://en.wikipedia.org/wiki/GUID
|
|
http://www.uefi.org/sites/default/files/resources/2_4_Errata_B.pdf
|
|
|
|
|
|
GPT is the partition map format of EFI, a successor of PC-BIOS.
|
|
Block size is always 512. GPT consists of a header block at block address 1 and
|
|
a partition table near the start of the medium. This is called the primary GPT.
|
|
There is a backup copy of header and table near the end of the medium.
|
|
|
|
GPT is particularly designed to co-exist with MBR. Officially only with a
|
|
Protective MBR which covers the whole medium (except the MBR itself) by
|
|
a single partition of type 0xee. Inofficially often with filesystem partitions
|
|
marked in both, GPT and MBR. In the latter case the booting firmware may
|
|
or may not prefer GPT over the MBR partition table.
|
|
GPT can co-exist with APM if APM block size is at least 1024. In this case,
|
|
the primary partition table will begin after the last APM entry block.
|
|
|
|
The header block format is:
|
|
Byte Range | Value | Meaning (little endian numbers, LBA unit is 512 byte)
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 7 | sig | Signature "EFI PART" (with no trailing zero)
|
|
8 - 11 | revision | Revision = {0x00, 0x00, 0x01, 0x00} meaning "1.0"
|
|
12 - 15 | head_size | Header size = 0x5c = 92
|
|
16 - 19 | head_crc | CRC-32 of this header while head_crc is 0
|
|
20 - 23 | reserved | = 0
|
|
24 - 31 | curr_lba | Location of this header block = 1
|
|
32 - 39 | backup_lba | Location of header backup block. See below.
|
|
40 - 47 | first_lba | First usable LBA for partitions
|
|
48 - 55 | last_lba | Last usable LBA for partitions
|
|
56 - 71 | guid | Disk GUID, Random
|
|
72 - 79 | part_start | Partition entries start
|
|
| | Normally this is 2. But to co-exist with APM, it
|
|
| might become some other number up to 62.
|
|
80 - 83 | entry_count| Number of partition entries
|
|
84 - 87 | entry_size | Size of a partition entry = 0x80 = 128
|
|
88 - 91 | p_arr_crc | CRC-32 of the partition array
|
|
92 - 511 | reserved | Must be 0
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
The CRC-32 algorithm can be characterized as follows:
|
|
The generating polynomial has the bit representation 0x104c11db7.
|
|
The seed value for a bit shifting division algorithm is 0x46af6449. It is
|
|
chosen so that the CRC of 0 bytes of input is 0x00000000.
|
|
The least significant bits of input bytes get processed first. I.e. bit0 of
|
|
the last input byte gets mapped to x exp (7 + 32), bit7 of this byte gets
|
|
mapped to x exp (0 + 32).
|
|
The resulting division residue gets bitwise mirrored. E.g. bit0 becomes bit31,
|
|
bit1 becomes bit30, and so on. Further it gets exored with 0xffffffff.
|
|
|
|
A GUID consists of a 32-bit integer, two 16-bit integers, and an array of
|
|
8 bytes. The integers are to be stored big-endian.
|
|
A globally registered class of GUID are the partition type GUIDs:
|
|
Basic data partition: a2 a0 d0 eb , e5 b9 , 33 44 , 87 c0 68 b6 b7 26 99 c7
|
|
HFS+ partition : 00 53 46 48 , 00 00 , aa 11 , aa 11 00 30 65 43 ec ac
|
|
EFI System partition: 28 73 2a c1 , 1f f8 , d2 11 , ba 4b 00 a0 c9 3e c9 3b
|
|
Note that the wikipedia list shows the first 32-bit word and the next two
|
|
16-bit words in little-endian interpretation.
|
|
|
|
The partition table is an array of entries. Each has a size of 128 bytes.
|
|
A partition table entry looks like:
|
|
|
|
Byte Range | Value | Meaning (numbers are stored little endian)
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 15 | type_guid | Partition type GUID
|
|
16 - 31 | part_guid | Unique partition GUID, Random
|
|
32 - 39 | start_lba | First LBA
|
|
40 - 47 | end_lba | Last LBA (inclusive)
|
|
48 - 55 | flags | Attribute flags
|
|
| | bit0= "System Partition" Do not alter.
|
|
| | bit2= Legacy BIOS bootable (MBR partition type 0x80)
|
|
| | bit60= read-only
|
|
56 - 127 | name | Characters encoded as UTF-16LE. Padded by 0-bytes.
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
|
|
About header field "Location of header backup block":
|
|
|
|
Near to the end of the image, after any data blocks which might be of interest
|
|
for the filesystems covered by GPT partitions, there is a backup of partition
|
|
table and header block.
|
|
The header block is supposed to mark the end of the usable medium. But libisofs
|
|
may have the need to add more data.
|
|
The partition table is stored directly before the header block. So it will
|
|
normally not begin at a 2 KiB block start.
|
|
|
|
The content of the backup partition table is the same as the one of the
|
|
primary table.
|
|
The backup header differs from the primary header by
|
|
Byte Range | Value | Meaning (little endian numbers, LBA unit is 512 byte)
|
|
---------- | ---------- | ----------------------------------------------------
|
|
16 - 19 | head_crc | CRC-32 of this header while head_crc is 0.
|
|
| | Is recomputed after the following changes.
|
|
24 - 31 | curr_lba | Location of this header block.
|
|
| | Shows own block address.
|
|
32 - 39 | backup_lba | Location of header backup block.
|
|
| | Points to primary header block = 1
|
|
72 - 79 | part_start | Partition entries start.
|
|
| | Points to start of backup partition table.
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
|
|
An EFI System partition usually contains the same data blocks as the El Torito
|
|
boot image for EFI. It is used for booting some Macs from (pseudo-) hard disk.
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
MIPS Volume Header
|
|
for MIPS Big Endian, e.g. SGI Indigo2
|
|
|
|
Sources:
|
|
cdrkit-1.1.10/genisoimage/boot-mips.c
|
|
by Steve McIntyre <steve@einval.com>
|
|
which refers to
|
|
genisovh by Florian Lohoff <flo@rfc822.org>
|
|
and Thiemo Seufer <seufer@csv.ica.uni-stuttgart.de>
|
|
who seem to have learned parameter settings from IRIX CD media
|
|
There are traces in the web which relate this to specs by
|
|
MIPS Computer Systems, Inc. , 1985
|
|
Silicon Graphics Computer Systems, Inc. , 2000
|
|
Mail conversations with Natalia Portillo.
|
|
|
|
|
|
The first 512 bytes of the media constitute the Volume Header.
|
|
Words are composed big-endian style.
|
|
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 3 | 0x0be5a941 | Magic number
|
|
4 - 5 | 0 | Root partition number
|
|
6 - 7 | 0 | Swap partition number
|
|
8 - 23 | 0 | One of the boot_name items from the Volume Directory
|
|
| | may be put here to choose for booting the entry with
|
|
| | that name.
|
|
| | (Obviously it may be empty if only one non-zero entry
|
|
| | exists in the Volume Directory.)
|
|
| |
|
|
24 - 71 | ========== | Device Parameters
|
|
| |
|
|
24 - 24 | 0 | Spiral addressing skew (unclear what this means)
|
|
25 - 25 | 0 | Words of 0 before header
|
|
26 - 26 | 0 | Words of 0 between hdr and data
|
|
27 - 27 | 0 | Spare sectors per cylinder
|
|
28 - 29 | num_cyl_l | Number of usable cylinder, lower two bytes
|
|
| | ((iso_size + BYTES_PER_SECTOR - 1) /
|
|
| | (SECTORS_PER_TRACK * BYTES_PER_SECTOR)) & 0xffff
|
|
30 - 31 | 0 | Starting head of volume 0
|
|
32 - 33 | 1 | Number of tracks per cylinder
|
|
34 - 34 | 0 | Depth of CTQ queue (unclear what this means)
|
|
35 - 35 | num_cyl_h | Number of usable cylinders, high byte
|
|
| | ((iso_size + BYTES_PER_SECTOR - 1) /
|
|
| | (SECTORS_PER_TRACK * BYTES_PER_SECTOR)) >> 16
|
|
36 - 37 | 0 | unused
|
|
38 - 39 | 32 | SECTORS_PER_TRACK
|
|
40 - 41 | 512 | BYTES_PER_SECTOR
|
|
42 - 43 | 0 | Sector interleave (unclear what this means)
|
|
44 - 47 | 0x00000034 | Controller characteristics composed from
|
|
| | DP_RESEEK 0x00000020 /* recalibrate as last resort */
|
|
| | DP_IGNOREERRORS 0x00000010
|
|
| | /* transfer data regardless of errors */
|
|
| | DP_TRKFWD 0x00000004
|
|
| | /* forward to replacement track */
|
|
48 - 51 | 0 | Bytes/sec for kernel stats
|
|
52 - 55 | 0 | Max num retries on data error
|
|
56 - 59 | 0 | ms per word to xfer, for iostat
|
|
60 - 71 | 0 | 6 parameter words for xylogics controllers
|
|
| |
|
|
72 - 311 | ========== | Volume Directory with 15 entries of 16 bytes each
|
|
| |
|
|
72 - 87 | ========== | Volume Directory Entry 1
|
|
72 - 79 | boot_name | Boot file basename, eventually padded by 0 to length 8
|
|
80 - 83 | boot_block | ISO 9660 LBA of boot file * 4, i.e. in blocks of 512
|
|
84 - 87 | boot_bytes | File length in bytes
|
|
| |
|
|
88 - 311 | see above | Volume Directory Entries 2 to 15
|
|
| |
|
|
312 - 504 | ========== | Partition Table with 16 entries of 12 bytes each
|
|
| |
|
|
312 - 407 | 0 | Unused partition entries 1 to 8
|
|
| |
|
|
408 - 419 | ========== | Partition Table Entry 9 for Volume Header
|
|
408 - 411 | part_blks | Number of 512 byte blocks in partition
|
|
| |(iso_size + (BYTES_PER_SECTOR - 1)) / BYTES_PER_SECTOR
|
|
412 - 415 | 0 | Start block of partition
|
|
416 - 419 | 0 | PTYPE_VOLHDR = Partition is volume header
|
|
| |
|
|
420 - 431 | 0 | Unused partition entry 10
|
|
| |
|
|
432 - 443 | ========== | Partition Table Entry 11 for Volume
|
|
432 - 435 | part_blks | Number of 512 byte blocks in partition
|
|
| |(iso_size + (BYTES_PER_SECTOR - 1)) / BYTES_PER_SECTOR
|
|
436 - 439 | 0 | Start block of partition
|
|
440 - 443 | 6 | PTYPE_VOLUME = Partition is entire volume
|
|
| |
|
|
444 - 503 | 0 | Unused partition entries 12 to 16
|
|
| |
|
|
504 - 507 | head_chk | Volume header checksum
|
|
| | The two's complement of bytes 0 to 503 read as big
|
|
| | endian unsigned 32 bit: sum(words) + head_chk == 0
|
|
| |
|
|
508 - 511 | 0 | Volume header end padding
|
|
| |
|
|
up to 2048 | 0 | ISO 9660 Block end padding
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
DEC Boot Block
|
|
for MIPS Little Endian , e.g. DECstation
|
|
|
|
Sources:
|
|
cdrkit-1.1.10/genisoimage/boot-mipsel.c
|
|
by Steve McIntyre <steve@einval.com>
|
|
which refers to
|
|
delo by Florian Lohoff <flo@rfc822.org>
|
|
and Thiemo Seufer <seufer@csv.ica.uni-stuttgart.de>
|
|
cdrkit-1.1.10/include/glibc_elf.h
|
|
by Steve McIntyre
|
|
which is based on
|
|
<elf.h> from GNUC C Library by Free Software Foundation, Inc.
|
|
|
|
|
|
There seems to be only one boot file possible.
|
|
Some information needs to be read out of the ELF headers of this boot file.
|
|
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 7 | 0 | Padding
|
|
| |
|
|
8 - 11 | 0x0002757a | Magic number
|
|
| |
|
|
12 - 15 | 1 | Mode /* 0: Single extent, 1: Multi extent boot */
|
|
| |
|
|
16 - 19 | load_adr | Load address /* Load below kernel */
|
|
| | Stems from ELF header of boot file.
|
|
| | See below Elf32_Phdr field p_vaddr.
|
|
| |
|
|
20 - 23 | exec_adr | Execution address /* And exec there */
|
|
| | Stems from ELF header of boot file.
|
|
| | See below Elf32_Ehdr field e_entry.
|
|
| |
|
|
24 - 31 | ========== | Boot Map Entry 1
|
|
| |
|
|
24 - 27 | seg_size | Segment size in file. Blocks of 512 bytes.
|
|
| | Stems from ELF header of boot file.
|
|
| | (Elf32_Phdr field p_filesz + 511) / 512;
|
|
| |
|
|
28 - 31 | seg_start | Segment file offset. Blocks 512 bytes.
|
|
| | ISO 9660 LBA of boot file * 4 plus offset which
|
|
| | stems from ELF header of boot file:
|
|
| | (Elf32_Phdr field p_offset + 511) / 512;
|
|
| |
|
|
32 - 431 | ========== | Boot Map Entries 2 to 51
|
|
| 0 |
|
|
| |
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
|
|
Elf32_Ehdr gets loaded from boot file byte address 0:
|
|
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 23 | | ( Magic number, file information )
|
|
| |
|
|
24 - 27 | e_entry | /* Entry point virtual address */
|
|
| = exec_adr | Needed for exec_adr
|
|
| |
|
|
28 - 31 | e_phoff | /* Program header table file offset */
|
|
| | Byte address of Elf32_Phdr
|
|
| |
|
|
|
|
Elf32_Phdr gets loaded from boot file byte_address Elf32_Ehdr.e_phoff :
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 3 | | ( Segment type )
|
|
| |
|
|
4 - 7 | p_offset | /* Segment file offset */
|
|
|-> seg_start| Needed for seg_start
|
|
| |
|
|
8 - 11 | p_vaddr | /* Segment virtual address */
|
|
| =load_adr | Needed for load_adr
|
|
| |
|
|
12 - 15 | | (Segment physical address)
|
|
| |
|
|
16 - 19 | p_filesz | /* Segment size in file */
|
|
|-> seg_size | Needed for seg_size
|
|
| |
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
SUN Disk Label and boot images
|
|
for SUN SPARC
|
|
|
|
Sources:
|
|
cdrtools-2.01.01a77/mkisofs/sunlabel.h
|
|
cdrtools-2.01.01a77/mkisofs/mkisofs.8
|
|
by Joerg Schilling
|
|
|
|
|
|
The Disk Label is written to the first 512 bytes of the image. It can mark
|
|
8 partitions (slices ) of which the first contains the ISO image. The other
|
|
7 may contain boot images.
|
|
Words are composed big-endian style. Block size is 512.
|
|
|
|
Boot images are provided externally. mkisofs arranges them after the end of
|
|
the ISO image so that each starts at a cylinder boundary (320 kB).
|
|
|
|
There is a mechanism in mkisofs which fills unused partitions by copies of
|
|
their predecessor in the partition table:
|
|
"If the special filename ... is used, the actual and all following
|
|
boot partitions are mapped to the previous partition.
|
|
If mkisofs is called with -G image -B ... all boot partitions are
|
|
mapped to the partition that contains the ISO9660 filesystem."
|
|
|
|
Disk Label components:
|
|
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 127 | label | ASCII Label
|
|
| | "CD-ROM Disc with Sun sparc boot created by ..."
|
|
| | mkisofs option -sparc-label
|
|
| |
|
|
128 - 263 | ========== | /* vtoc inclusions from AT&T SVr4 */
|
|
| |
|
|
128 - 131 | 1 | Layout version
|
|
132 - 139 | 0 | /* volume name */
|
|
140 - 141 | 8 | Number of partitions
|
|
| |
|
|
142 - 173 | ========== | 8 partition entries of 4 bytes
|
|
| |
|
|
142 - 145 | ========== | Entry for partition 1
|
|
142 - 143 | 4 | ID tag of partition: 4 = User partition
|
|
144 - 145 | 0x10 | Permissions: 0x10 = read-only
|
|
| |
|
|
146 - 149 | ========== | Entry for partition 2
|
|
146 - 147 | id_tag2 | ID tag of partition:
|
|
| | 0 = unused
|
|
| | 2 = Root partition with boot image
|
|
148 - 149 | perm2 | Permissions:
|
|
| | 0 = unused
|
|
| | 0x10 = read-only (if used)
|
|
| |
|
|
150 - 173 | ========== | Entries for partition 3 to 8.
|
|
| | See above: Entry for partition 2
|
|
| |
|
|
174 - 175 | 0 | Padding
|
|
| |
|
|
176 - 187 | 0 | /* info for mboot */
|
|
| |
|
|
188 - 191 | 0x600ddeee | /* to verify vtoc sanity */
|
|
| |
|
|
192 - 231 | 0 | Reserved
|
|
| |
|
|
232 - 263 | 0 | 8 Timestamps of yet unknown format
|
|
| |
|
|
264 - 419 | 0 | Padding
|
|
| |
|
|
420 - 443 | ========== | Disk properties
|
|
| |
|
|
420 - 421 | 350 | Rotations per minute
|
|
422 - 423 | 2048 | Number of physical cylinders (fixely 640 MB)
|
|
424 - 425 | 0 | /* alternates per cylinder */
|
|
426 - 429 | 0 | /* obsolete */
|
|
430 - 431 | 1 | /* interleave factor */
|
|
432 - 433 | 2048 | Number of data cylinders (fixely 640 MB)
|
|
434 - 435 | 0 | /* # of alternate cylinders */
|
|
436 - 437 | 1 | Number of heads per cylinder (i.e. 1 cyl = 320 kB)
|
|
438 - 439 | 640 | Number of sectors per head (i.e. 1 head = 320 kB)
|
|
440 - 443 | 0 | /* obsolete */
|
|
| |
|
|
444 - 507 | ========== | Partition table
|
|
| |
|
|
444 - 451 | ========== | Partition table entry #1
|
|
| |
|
|
444 - 447 | start_cyl | Start cylinder
|
|
| |
|
|
448 - 451 | num_blocks | Number of 512-byte blocks in partition
|
|
| |
|
|
452 - 507 | ========== | Partition table entries #2 to #8
|
|
| ... | See above Partition table entry #1
|
|
| |
|
|
508 - 509 | 0xdabe | Magic Number
|
|
| |
|
|
510 - 511 | checksum | The result of exoring 2-byte words 0 to 254
|
|
| |
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
GRUB2 SUN SPARC Core File Address
|
|
|
|
Sources:
|
|
Mail conversations with Vladimir Serbinenko.
|
|
|
|
GRUB2 lets libisofs write after the disk label block the address and size of a
|
|
data file in the ISO image. E.g. of /boot/grub/sparc64-ieee1275/core.img.
|
|
This is combined with a SUN Disk Label which exposes only the single partition
|
|
describing the overall ISO filesystem size.
|
|
|
|
Byte Range | Value | Meaning
|
|
------------ | ---------- | --------------------------------------------------
|
|
512 - 551 | opaque | Code and data provided by GRUB2
|
|
| |
|
|
552 - 559 | offset | Start byte number of the file. 64-bit big-endian.
|
|
| |
|
|
560 - 563 | size | Number of bytes in the file. 32-bit big-endian.
|
|
| |
|
|
564 - 32767 | opaque | Code and data provided by GRUB2
|
|
| |
|
|
------------ | ---------- | --------------------------------------------------
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
PowerPC Reference Platform (PReP)
|
|
for IBM PowerPC
|
|
|
|
Sources:
|
|
Mail conversations with Vladimir Serbinenko.
|
|
|
|
|
|
PReP boots via a MBR partition containing only raw ELF and having type 0x41.
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
Common Hardware Reference Platform (CHRP)
|
|
for IBM PowerPC
|
|
|
|
Sources:
|
|
Mail conversations with Vladimir Serbinenko.
|
|
http://stuff.mit.edu/afs/sipb/contrib/doc/specs/protocol/chrp/chrp1_7a.pdf
|
|
https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/W51a7ffcf4dfd_4b40_9d82_446ebc23c550/page/PowerLinux%20Boot%20howto
|
|
|
|
CHRP is marked by an MBR partition entry of type 0x96 spanning the whole
|
|
ISO 9660 image.
|
|
|
|
The specs in chrp1_7a.pdf promise that CHRP also recognizes ISO 9660 file
|
|
systems on unpartitioned disks. (See 11.1.1. Media Layout Format)
|
|
|
|
The firmware looks up a file /ppc/bootinfo.txt which in SGML-ish tag
|
|
<boot-script> contains firmware commands.
|
|
E.g. to execute the binary /boot/grub/powerpc.elf as first stage of GRUB2:
|
|
<boot-script>boot &device;:\boot\grub\powerpc.elf</boot-script>
|
|
|
|
Vladimir Serbinenko stated:
|
|
PReP boot may be preferable. At least it can co-exist with other partitions
|
|
in the ISO image [without causing overlapping between partitions].
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
HP-PA via PALO header version 4
|
|
for HP PA-RISC
|
|
|
|
Sources:
|
|
cdrkit-1.1.10/genisoimage/boot-hppa.c
|
|
by Steve McIntyre <steve@einval.com>
|
|
who states "Heavily inspired by palo"
|
|
|
|
This format is expected by PALO versions before 1.92. Their source code defines
|
|
PALOHDRVERSION as 4. The format also serves as fallback for newer versions,
|
|
which expect header version 5, if a 0-byte is found at byte position 1024.
|
|
|
|
There are five parameters which get encoded into the first 248 bytes of the
|
|
System Area: cmdline, bootloader, 32-bit kernel, 64-bit kernel, and ramdisk.
|
|
They are all mandatory.
|
|
While cmdline is simply a string of at most 127 characters, the other four
|
|
point to data files inside the ISO image.
|
|
|
|
All numbers are recorded big endian.
|
|
|
|
Boot sector components:
|
|
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 1 | 0x8000 | Magic
|
|
| |
|
|
2 - 6 | "PALO" | Zero terminated string
|
|
| |
|
|
7 - 7 | 4 | Version
|
|
| |
|
|
8 - 11 | kern32_adr | Byte address of the "HPPA 32-bit kernel" file
|
|
| | genisoimage option -hppa-kernel-32
|
|
12 - 15 | kern32_len | Byte count of the "HPPA 32-bit kernel" file
|
|
| |
|
|
16 - 19 | ramdsk_adr | Byte address of the "HPPA ramdisk" file
|
|
| | genisoimage option -hppa-ramdisk
|
|
20 - 23 | ramdsk_len | Byte count of the "HPPA ramdisk" file
|
|
| |
|
|
24 - 151 | cmdline | "Command line"
|
|
| | genisoimage option -hppa-cmdline
|
|
| |
|
|
232 - 235 | kern64_adr | Byte address of the "HPPA 64-bit kernel" file
|
|
| | genisoimage option -hppa-kernel-64
|
|
236 - 239 | kern64_len | Byte count of the "HPPA 64-bit kernel" file
|
|
| |
|
|
240 - 243 | bootld_adr | Byte address of the "HPPA bootloader" file
|
|
| | genisoimage option -hppa-bootloader
|
|
244 - 247 | bootld_len | Byte count of the "HPPA bootloader" file
|
|
| |
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
HP-PA via PALO header version 5
|
|
for HP PA-RISC
|
|
|
|
Sources:
|
|
Public mail conversations with Helge Deller, beginning with
|
|
https://lists.debian.org/debian-hppa/2014/01/msg00016.html
|
|
http://git.kernel.org/cgit/linux/kernel/git/deller/palo.git/tree/lib/
|
|
(especially struct firstblock in common.h and struct partition in part.h)
|
|
|
|
This format is expected by PALO versions 1.92 or higher. They fall back to
|
|
header version 4 if a 0-byte is found at byte position 1024.
|
|
Their source code defines PALOHDRVERSION as 5.
|
|
|
|
There are five parameters which get encoded into the first 2048 bytes of the
|
|
System Area: cmdline, bootloader, 32-bit kernel, 64-bit kernel, and ramdisk.
|
|
They are all mandatory.
|
|
While cmdline is simply a string of at most 1023 characters, the other four
|
|
point to data files inside the ISO image.
|
|
|
|
Several fields of the firstblock shall be hardcoded to 0, on advise of
|
|
Helge Deller. Their description is shown in round brackets.
|
|
|
|
All numbers are recorded big endian.
|
|
Except flags, all 4-byte integers are signed.
|
|
|
|
Boot sector components:
|
|
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 1 | 0x8000 | Magic
|
|
| |
|
|
2 - 6 | "PALO" | Zero terminated string
|
|
| |
|
|
7 - 7 | 5 | Version
|
|
| |
|
|
8 - 11 | kern32_adr | Byte address of the 32-bit kernel file
|
|
| |
|
|
12 - 15 | kern32_len | Byte count of the 32-bit kernel file
|
|
| |
|
|
16 - 19 | ramdsk_adr | Byte address of the ramdisk file
|
|
| |
|
|
20 - 23 | ramdsk_len | Byte count of the ramdisk file
|
|
| |
|
|
24 - 141 | 0 | All 0s. Old command line of version 4.
|
|
| |
|
|
| |
|
|
220 - 223 | 0 | (Length of uncompressed 32-bit kernel)
|
|
| |
|
|
224 - 227 | 0 | (Length of uncompressed 64-bit kernel)
|
|
| |
|
|
228 - 231 | 0 | (flags)
|
|
| |
|
|
232 - 235 | kern64_adr | Byte address of the 64-bit kernel file
|
|
| |
|
|
236 - 239 | kern64_len | Byte count of the 64-bit kernel file
|
|
| |
|
|
240 - 243 | ipl_adr | Byte address of the bootloader file
|
|
| |
|
|
244 - 247 | ipl_len | Byte count of the bootloader file
|
|
| |
|
|
248 - 251 | 0 | (ipl_entry: offset to first command in bootloader)
|
|
| |
|
|
446 - 511 | 0 | (MBR partition table and signature)
|
|
| |
|
|
1024 -2047 | cmdline | Zero terminated command line of up to
|
|
| | 1023 characters
|
|
| |
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
DEC Alpha SRM boot sector
|
|
for Alpha architecture
|
|
|
|
Sources:
|
|
http://www.tldp.org/HOWTO/text/SRM-HOWTO
|
|
SRM Firmware Howto - Rich Payne, and David Huggins-Daines
|
|
cdrkit-1.1.10/genisoimage/boot-alpha.c
|
|
by Steve McIntyre
|
|
who states "Heavily inspired by isomarkboot by David Mosberger in 1996"
|
|
mail conversations with Helge Deller
|
|
|
|
The SRM firmware expects a Secondary Bootstrap Loader program, which usually
|
|
is a data file of the ISO filesystem. This loader is announced by size and
|
|
block address in the first 512 bytes of the System Area.
|
|
SRM accepts the boot sector and executes the loader if the checksum matches.
|
|
|
|
All numbers are recorded as unsigned 64 bit little endian.
|
|
|
|
Boot sector components:
|
|
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - ? | boot_string| genisoimage writes
|
|
| | "Linux/Alpha aboot for ISO filesystem."
|
|
| | with terminating zero byte.
|
|
| |
|
|
? - 479 | 0 | Unused / undefined.
|
|
| |
|
|
480 - 487 | length | Size of boot loader file in units of 512 bytes.
|
|
| |
|
|
488 - 495 | address | LBA of the boot loader file in units of 512 bytes.
|
|
| |
|
|
496 - 503 | flag | "Always 0"
|
|
| |
|
|
504 - 511 | checksum | Sum of 64 bit words 0 to 63 (bytes 0 to 503).
|
|
| |
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
Combinations of boot mechanisms
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
SYSLINUX Isohybrid MBR
|
|
|
|
Sources:
|
|
syslinux-3.72/utils/isohybrid , a perl script by H. Peter Anvin = hpa.
|
|
Mailing list conversations with hpa.
|
|
|
|
|
|
An isohybrid MBR directs the booting BIOS to an ISOLINUX boot image which
|
|
is also the target of an El Torito boot catalog entry.
|
|
For that purpose one has to take an MBR template and has to set a few bytes
|
|
to values which sufficiently describe the ISO image and the boot image file.
|
|
|
|
Words are composed little-endian style.
|
|
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 431 | = opaque = | Syslinux machine code provided by MBR template
|
|
| |
|
|
432 - 439 | hd_bootlba | Address of the ISOLINUX boot image file in the
|
|
| | ISO image. Counted in 512 byte blocks.
|
|
| |
|
|
440 - 443 | mbr_id | Random number
|
|
444 - 445 | 0 | Padding
|
|
| |
|
|
446 - 509 | ========== | Partition table
|
|
| |
|
|
446 - 461 | part_entry | Partition table entry 1 describing ISO image size
|
|
| | rounded up to the next full MiB. The partition starts
|
|
| | at LBA 0. (I.e. contrary to tradition.)
|
|
| | See above for partition table entry format.
|
|
| |
|
|
462 - 509 | 0 | Unused partition entries 2 to 4
|
|
510 - 511 | 0xaa55 | MBR signature
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
The ISO image file gets padded up to the next full MiB.
|
|
|
|
hpa about MBR templates and partition table filesystem types:
|
|
|
|
"[MBR templates] are available in the Syslinux build tree under the names:
|
|
mbr/isohdp[fp]x*.bin
|
|
The default probably should be mbr/isohdppx.bin, but it's ultimately up
|
|
to the user.
|
|
[...]
|
|
Note: the filesystem type is largely arbitrary, in theory it can be any
|
|
value other than 0x00, 0x05, 0x0f, 0x85, 0xee, or 0xef. 0x17 ("Windows
|
|
IFS Hidden") seems safeish, some people believe 0x83 (Linux) is better.
|
|
"
|
|
|
|
|
|
>>> SYSLINUX isohybrid for MBR, UEFI and x86-Mac
|
|
|
|
Sources:
|
|
http://mjg59.dreamwidth.org/11285.html
|
|
http://mjg59.fedorapeople.org/Fedora-LiveCD.iso
|
|
http://opensource.apple.com/source/IOStorageFamily/IOStorageFamily-116/IOApplePartitionScheme.h (typedef struct Block0)
|
|
http://www.informit.com/articles/article.aspx?p=376123&seqNum=3
|
|
http://en.wikipedia.org/wiki/GUID_Partition_Table
|
|
http://en.wikipedia.org/wiki/GUID
|
|
syslinux-4.05/utils/isohybrid.c
|
|
|
|
>>> Motivation: What systems will use the additional data ? amd64 UEFI ?
|
|
|
|
This is a very condensed format which exposes a lot of entry points for boot
|
|
firmware. It disobeys some of the prescriptions in the previous chapter.
|
|
|
|
Byte Range | Value | Meaning
|
|
-------------- | ---------- | -------------------------------------------------
|
|
0 - 511 | mbr | Isohybrid MBR pointing to x86 boot image file,
|
|
| | with three entries in its partition map.
|
|
| | It shares its first 32 bytes with apm_head.
|
|
0 - 31 | apm_head | Mock-up of the start of the first block of
|
|
| | an Apple Partition Map (APM).
|
|
446 - 461 | mbr_entry1 | Partition table entry 1 describing the size of
|
|
| | the ISO image plus the backup GPT, padded up to
|
|
| | the next full MiB.
|
|
462 - 477 | mbr_entry2 | Entry 2 describing the EFI VFAT boot image.
|
|
478 - 493 | mbr_entry3 | Entry 3 describing the HFS+ boot image.
|
|
| |
|
|
512 - 1023 | gpt_head | GPT header describing the GPT partition array.
|
|
1024 - 2047 | unused |
|
|
2048 - 4095 | apm_entry1 | APM entry 1 describing APM entries 1 to 3.
|
|
4096 - 6143 | apm_entry2 | APM entry 2 describing the EFI VFAT boot image.
|
|
6144 - 8195 | apm_entry3 | APM entry 3 describing the HFS+ boot image.
|
|
8192 - 8319 | gpt_entry1 | GPT partition entry 1 for the ISO image size.
|
|
8320 - 8447 | gpt_entry2 | GPT partition entry 2 for EFI VFAT boot image,
|
|
8448 - 8575 | gpt_entry3 | GPT partition entry 3 for the HFS+ boot image.
|
|
8576 - 24575 | gtp_empty | Empty GPT partition entries 4 to 128.
|
|
24576 - 32767 | unused |
|
|
32768 - 34815 | iso_pvd | ISO 9660 superblock
|
|
34816 - 36863 | el_torito | EL Torito boot block pointing to a boot catalog
|
|
| | with entries for the MBR boot image (platform id
|
|
| | 0x00), and for the two other boot images
|
|
| | (platform id 0xef)
|
|
-------------- | ---------- | -------------------------------------------------
|
|
|
|
|
|
For the purpose of booting, there may be two EFI boot image files in the
|
|
ISO image. A VFAT image and a HFS+ image. The content of both is not in the
|
|
scope of this document.
|
|
These boot images get announced by EL Torito boot catalog entries with
|
|
Platform Id 0xef.
|
|
|
|
|
|
Newer SYSLINUX MBR templates begin by 32 bytes of machine code which are
|
|
intentionally non-essential:
|
|
33 ed 90 90 90 90 90 90 90 90 90 90 90 90 90 90
|
|
90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90
|
|
They may be overwritten by other bytes which must not produce errors or
|
|
undesirable side effects when executed as x86 machine code.
|
|
The following 32 bytes from block 0 of an Apple Partition Map (APM) are such
|
|
harmless code. They stem from Fedora-LiveCD.iso by Matthew Garrett:
|
|
45 52 08 00 00 00 90 90 00 00 00 00 00 00 00 00
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
They do not depend on any properties of the ISO image or the information
|
|
that is described in the following text.
|
|
|
|
The layout of Block0 is constant:
|
|
|
|
Byte Range | Value | Meaning (all numbers are stored big endian)
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 1 | sig | Signature 0x45 = 'E' , 0x52 = 'R'
|
|
2 - 3 | block_size | 0x0800 = 2048
|
|
4 - 7 | block_count| 0x9090 = 37008
|
|
8 - 9 | dev_type | obscure: "device type" = 0
|
|
10 - 11 | dev_id | obscure: "device id" = 0
|
|
12 - 15 | drv_data | obscure: "driver data" = 0
|
|
16 - 17 | drv_count | obscure: "driver descriptor count" = 0
|
|
18 - 81 | drv_map | obscure: "driver descriptor table"
|
|
| | with 8 entries of 16 bytes each
|
|
| | first 14 bytes are 0
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
The block_count of 0x9090 is pure fantasy. It shall only mark the disc as
|
|
not empty.
|
|
|
|
The data block ranges of the two EFI boot images get described by MBR
|
|
partition entries 2 and 3, which thus claim blocks inside of partition 1.
|
|
This partition nesting is acceptable to some EFI implementations only if the
|
|
type of partition 1 is 0x00.
|
|
|
|
The MBR partition entry number 1 is
|
|
80 00 01 00 00 3f a0 89 00 00 00 00 00 50 14 00
|
|
It marks the partition as bootable, starting at block 0, with a size that
|
|
is the smallest full MiB not smaller than the ISO image size + 18 KiB.
|
|
(The 18 KiB are needed for the GPT backup.)
|
|
The ISO image has a size of 332362 blocks of 2K = 1329448 * 512 = 649.14 MiB.
|
|
The partition size is 0x145000 = 1331200 * 512 = 650 MiB.
|
|
Start C/H/S = 0/0/1, type is 0x0 ("Empty"), end C/H/S is 649/63/32.
|
|
|
|
Partition 2:
|
|
00 fe ff ff ef fe ff ff a4 00 00 00 70 04 00 00
|
|
Start block is 0xa4 = 164 * 512 = 41 * 2048. The VFAT image file.
|
|
Partition size is 0x0470 = 1136 * 512. The size of that file.
|
|
Start C/H/S = 1023/254/63, type 0xef (fdisk says: "EFI (FAT-12/16/"),
|
|
end C/H/S = 1023/254/63.
|
|
|
|
Partition 3:
|
|
00 fe ff ff 00 fe ff ff 44 05 00 00 c0 08 00 00
|
|
Start block is 0x0544 = 1348 * 512 = 337 * 2048. The HFS+ image file.
|
|
Partition size is 0x08c0 = 2240 * 512. The size of that file.
|
|
Start C/H/S = 1023/254/63, type 0x00 ("Empty"), end C/H/S = 1023/254/63.
|
|
|
|
|
|
The second 512-block in the ISO image is the GPT header.
|
|
|
|
45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00
|
|
E F I P A R T
|
|
13 db 71 5d 00 00 00 00 01 00 00 00 00 00 00 00
|
|
fe 4f 14 00 00 00 00 00 30 00 00 00 00 00 00 00
|
|
de 4f 14 00 00 00 00 00 73 23 c8 79 19 e6 97 4d
|
|
95 17 69 30 c5 38 e2 99 10 00 00 00 00 00 00 00
|
|
80 00 00 00 80 00 00 00 5b 6b 8a 65
|
|
|
|
Byte Range | Value | Meaning (little endian numbers, LBA unit is 512 byte)
|
|
---------- | ---------- | ----------------------------------------------------
|
|
12 - 15 | head_size | Header size = 0x5c = 92
|
|
24 - 31 | curr_lba | Location of this header block = 0x1
|
|
32 - 39 | backup_lba | Location of header backup block = 0x144ffe = 1331198
|
|
| | This is 1 KiB before the end of MBR partition 1
|
|
| | (but should be 512 bytes).
|
|
| | (Potential isohybrid.c bug #1:
|
|
| | Backup GPT is dislocated by 512 bytes.)
|
|
40 - 47 | first_lba | First usable LBA for partitions = 0x30 = 48
|
|
48 - 55 | last_lba | Last usable LBA for partitions = 0x144fde = 1331166
|
|
56 - 71 | guid | Disk GUID
|
|
| | Random, produced by uuid_generate(),
|
|
| | 32,16,16 byte swapped
|
|
72 - 79 | part_start | Partition entries start LBA = 0x10 = 16 = byte 0x2000
|
|
| | (This is unusual. It leaves room for the Apple
|
|
| | partition map entries.)
|
|
80 - 83 | entry_count| Number of partition entries 0x80 = 128
|
|
84 - 87 | entry_size | Size of a partition entry = 0x80 = 128
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
|
|
Because the block size was announced as 2048, the first Apple partition map
|
|
entry is located at byte 0x800 = 2048.
|
|
It describes the partition map itself:
|
|
50 4d 00 00 00 00 00 03 00 00 00 01 00 00 00 10
|
|
P M
|
|
41 70 70 6c 65 00 00 00 00 00 00 00 00 00 00 00
|
|
A p p l e
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
41 70 70 6c 65 5f 70 61 72 74 69 74 69 6f 6e 5f
|
|
A p p l e _ p a r t i t i o n _
|
|
6d 61 70 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
m a p
|
|
00 00 00 00 00 00 00 0a 00 00 00 03 00 00 00 00
|
|
|
|
|
|
Byte Range | Value | Meaning (all numbers are stored big endian)
|
|
---------- | ---------- | ----------------------------------------------------
|
|
4 - 7 | map_entries| "number of partition entries" = 3
|
|
8 - 11 | start_block| "physical block start of partition" = 1
|
|
12 - 15 | block_count| "physical block count of partition" = 16
|
|
| | (Potential isohybrid.c bug #2:
|
|
| | The value of 16 claims the ISO 9660 PVD as part of
|
|
| | the partition table. It should be 4 instead.)
|
|
16 - 47 | name | Partition name = "Apple"
|
|
48 - 79 | type | Type string = "Apple_partition_map"
|
|
80 - 83 | lb_start | Logical block start = 0
|
|
84 - 87 | lb_count | Logical block count = 10
|
|
88 - 91 | flags | Status flags = 3 (valid, allocated)
|
|
92 - 95 | boot_block | Logical start block number of boot code = 0
|
|
96 - 99 | boot_bytes | Number of bytes in boot code = 0
|
|
100 - 119 | | More boot code stuff = 0
|
|
120 - 135 | processor | "processor type" = 0
|
|
136 - 511 | reserved |
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
(Potential isohybrid.c bug #2:
|
|
Apple partition map entries bear the block count for blocks of 512 bytes
|
|
whereas Apple Block0 announces blocks of 2048 bytes.)
|
|
|
|
The next Apple partition map entry is at byte 0x1000 = 4096:
|
|
|
|
50 4d 00 00 00 00 00 03 00 00 00 29 00 00 04 70
|
|
45 46 49 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
E F I
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
41 70 70 6c 65 5f 48 46 53 00 00 00 00 00 00 00
|
|
A p p l e _ H F S
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
00 00 00 00 00 00 04 70 00 00 00 33 00 00 00 00
|
|
|
|
3 partitions, start block is 0x29 = 41,
|
|
block count is 0x0470 = 1136 (should be 284), name is "EFI",
|
|
type is "Apple_HFS" (although this is a FAT image),
|
|
logical block start = 0, lb_count = 1136 (should be 284),
|
|
flags = 0x33 : valid, allocated, readable, writable.
|
|
This points to file /isolinux/efiboot.img in the ISO image.
|
|
(Potential isohybrid.c bug #2:
|
|
Apple partition map entries bear the block count for blocks of 512 bytes
|
|
whereas Apple Block0 announces blocks of 2048 bytes.)
|
|
|
|
At byte 0x1800 = 6144, there is Apple partition map entry 3:
|
|
|
|
50 4d 00 00 00 00 00 03 00 00 01 51 00 00 08 c0
|
|
45 46 49 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
E F I
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
41 70 70 6c 65 5f 48 46 53 00 00 00 00 00 00 00
|
|
A p p l e _ H F S
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
00 00 00 00 00 00 08 c0 00 00 00 33 00 00 00 00
|
|
|
|
3 partitions, start block is 0x0151 = 337 (LBA of /isolinux/macboot.img),
|
|
block count = 0x08c0 = 2240 (should be 560), name is "EFI",
|
|
type is "Apple_HFS", logical block start = 0, lb_count = 2240 (should be 560),
|
|
flags = 0x33 : valid, allocated, readable, writable.
|
|
(Potential isohybrid.c bug #2:
|
|
Apple partition map entries bear the block count for blocks of 512 bytes
|
|
whereas Apple Block0 announces blocks of 2048 bytes.)
|
|
|
|
At byte 0x2000 = 8192 begins the GPT partition array.
|
|
It ends at byte 0x4000 = 16384.
|
|
|
|
a2 a0 d0 eb e5 b9 33 44 87 c0 68 b6 b7 26 99 c7
|
|
a1 87 a1 ba 4d 2c 27 45 ae 05 cf ab a6 fa 87 c1
|
|
00 00 00 00 00 00 00 00 28 49 14 00 00 00 00 00
|
|
00 00 00 00 00 00 00 00 49 53 4f 48 79 62 72 69
|
|
I S O H y b r i
|
|
64 20 49 53 4f 00 49 53 4f 48 79 62 72 69 64 00
|
|
d I S O I S O H y b r i d
|
|
41 70 70 6c 00 00 00 00 00 00 00 00 00 00 00 00
|
|
A p p l
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
|
|
Byte Range | Value | Meaning (numbers are stored little endian)
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 15 | type_guid | Partition type GUID = Basic data partition
|
|
| | Wikipedia: "EBD0A0A2-B9E5-4433-87C0-68B6B72699C7"
|
|
| | (Note: The first three words are shown byte swapped)
|
|
16 - 31 | part_guid | Unique partition GUID
|
|
| | Random, produced by uuid_generate()
|
|
| | 32,16,16 byte swapped
|
|
32 - 39 | start_lba | First LBA = 0
|
|
40 - 47 | end_lba | Last LBA (inclusive) = 0x144828 = 1329448
|
|
| | This is the ISO image size in blocks of 512.
|
|
| | (Potential isohybrid.c bug #3:
|
|
| | The end_lba in the first GPT entry should be 1 less
|
|
| | than the count of 512 byte blocks of the ISO image.)
|
|
48 - 55 | flags | Attribute flags = 0
|
|
56 - 127 | name | Wikipedia says UTF-16LE.
|
|
| | (Potential isohybrid.c bug #4:
|
|
| | The name in Fedora-LiveCD.iso is 8 bit and result
|
|
| | of faulty memory operation on a text constant.)
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
Next entry is at 0x2800 = 10240:
|
|
|
|
a2 a0 d0 eb e5 b9 33 44 87 c0 68 b6 b7 26 99 c7
|
|
c8 de c8 1f fb f0 51 40 8c 8a d2 f6 b1 46 16 dc
|
|
a4 00 00 00 00 00 00 00 13 05 00 00 00 00 00 00
|
|
00 00 00 00 00 00 00 00 49 53 4f 48 79 62 72 69
|
|
I S O H y b r i
|
|
64 00 41 70 70 6c 65 00 41 70 70 6c 00 00 00 00
|
|
d A p p l e A p p l
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
|
|
Partition type GUID : "EBD0A0A2-B9E5-4433-87C0-68B6B72699C7" = Basic data
|
|
Start at block 0xa4 = 164 * 512 = 41 * 2048. The VFAT image file.
|
|
Last block is 0x0513 = 1299 = 164 + 1135. This end is correct.
|
|
(Potential isohybrid.c bug #4:
|
|
Wrong character set and incidential bytes in GPT partition name.)
|
|
(Potential isohybrid.c bug #5:
|
|
The EFI System Partition should have type GUID :
|
|
"C12A7328-F81F-11D2-BA4B-00A0C93EC93B")
|
|
|
|
Next entry at byte 0x02100 = 8448:
|
|
|
|
00 53 46 48 00 00 aa 11 aa 11 00 30 65 43 ec ac
|
|
c8 de c8 1f fb f0 51 40 8c 8a d2 f6 b1 46 16 dc
|
|
44 05 00 00 00 00 00 00 03 0e 00 00 00 00 00 00
|
|
00 00 00 00 00 00 00 00 49 53 4f 48 79 62 72 69
|
|
I S O H y b r i
|
|
64 00 41 70 70 6c 65 00 41 70 70 6c 00 00 00 00
|
|
d A p p l e A p p l
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
|
|
Partition type GUID : "48465300-0000-11AA-AA11-00306543ECAC" = HFS+
|
|
Start block is 0x0544 = 1348 * 512 = 337 * 2048. The HFS+ image file.
|
|
Last block is 0x0e03 = 3587 = 1348 + 2239. Correct.
|
|
(Potential isohybrid.c bug #4:
|
|
Wrong character set and incidential bytes in GPT partition name.)
|
|
|
|
The rest of the System Area is 0 up to the Primary Volume Descriptor
|
|
at block 16.
|
|
|
|
|
|
The ISO image file gets padded up to full MiB with sufficient room for the GPT
|
|
backup which is stored near the very end of the image file. There is need for
|
|
at least 16.5 KiB, which effectively occupy 18 KiB.
|
|
|
|
The backup partition array is stored 17 KiB before the end of MBR partition 1,
|
|
which is also the end of the image file.
|
|
(Potential isohybrid.c bug #1:
|
|
Wikipedia suggests "LBA -33" counted from end. This would be 16.5 KiB before
|
|
end.)
|
|
|
|
The GPT header is stored 1 KiB before the end of MBR partition 1.
|
|
(Potential isohybrid.c bug #1:
|
|
Wikipedia suggests "LBA -1" counted from end. This would be 512 bytes.)
|
|
|
|
45 46 49 20 50 41 52 54 00 00 01 00 5c 00 00 00
|
|
E F I P A R T
|
|
f6 61 10 1c 00 00 00 00 fe 4f 14 00 00 00 00 00
|
|
01 00 00 00 00 00 00 00 30 00 00 00 00 00 00 00
|
|
de 4f 14 00 00 00 00 00 73 23 c8 79 19 e6 97 4d
|
|
95 17 69 30 c5 38 e2 99 de 4f 14 00 00 00 00 00
|
|
80 00 00 00 80 00 00 00 5b 6b 8a 65
|
|
|
|
It differs by its own CRC and by some of its parameters:
|
|
Own address is 0x144ffe. The backup lba is 0x01 = Primary GPT header.
|
|
Partition entries start is 0x144fde
|
|
(Potential isohybrid.c bug #1:
|
|
This overlaps with the last usable LBA. The backup GPT must move up by
|
|
512 bytes.)
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
GRUB2 grub-mkrescue MBR
|
|
|
|
Sources:
|
|
Mailing list conversations with Vladimir Serbinenko.
|
|
|
|
|
|
The MBR file that is used with older versions of GRUB2 script grub-mkrescue
|
|
needs only a partition table entry which describes the image size.
|
|
Newer versions get patched by the block address of the content of the first
|
|
El Torito boot image. See grub-mkrescue use of xorrisofs option --grub2-mbr.
|
|
|
|
Byte Range | Value | Meaning
|
|
---------- | ---------- | ----------------------------------------------------
|
|
0 - 431 | = opaque = | GRUB2 machine code provided by MBR template
|
|
| |
|
|
432 - 439 | bootimg_adr| With newer versions of grub-mkrescue:
|
|
| | Block address of the start of the boot image file
|
|
| | content plus 4. Block size is 512.
|
|
| | 64 bit Little-endian.
|
|
| |
|
|
440 - 445 | = opaque = | provided by MBR template
|
|
| |
|
|
446 - 509 | ========== | Partition table
|
|
| |
|
|
446 - 461 | part_entry | Partition table entry 1 describing ISO image size
|
|
| | Peculiar is the start offset of 1 block.
|
|
| | This prevents mounting of the partition.
|
|
| | See above for partition table entry format.
|
|
| |
|
|
462 - 509 | 0 | Unused partition entries 2 to 4
|
|
510 - 511 | 0xaa55 | MBR signature
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
Vladimir Serbinenko about the partition table entry:
|
|
"Currently we use first and not last entry. You need to:
|
|
1) Zero-fill 446-510
|
|
2) Put 0x55, 0xAA into 510-512
|
|
3) Put 0x80 (for bootable partition), 0, 2, 0 (C/H/S of the start), 0xcd
|
|
(partition type), [3 bytes of C/H/S end], 0x01, 0x00, 0x00, 0x00 (LBA
|
|
start in little endian), [LBA end in little endian] at 446-462
|
|
"
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
>>> Mac and/or PowerPC bootable GRUB2 image with HFS+/FAT, APM,
|
|
EFI GPT partition, PreP MBR partition, mountable FAT partition
|
|
|
|
>>> ? With PC-BIOS MBR x86 Code ?
|
|
|
|
This storage layout was mainly defined by Vladimir Serbinenko. It relies much
|
|
on the embedded HFS+/FAT filesystem for which he provided the code to libisofs.
|
|
|
|
Start Blocks (2 KiB):
|
|
0 System Area
|
|
16 Volume Descriptors
|
|
TREE ISO-RR tree, Joliet tree, other trees and meta data, except HFS+/FAT
|
|
EFI EFI boot image partition (optional)
|
|
PREP Prep image partition (optional)
|
|
HFAT HFS+/FAT metadata (optional)
|
|
DATA Data file content (including El Torito boot images)
|
|
HFSB HFS superblock backup (if HFS+/FAT metadata)
|
|
TAIL Further tails and paddings (optional)
|
|
GPTB GPT backup (if GPT in System Area)
|
|
END End of ISO image
|
|
|
|
System Area may contain simultaneously:
|
|
MBR (x86 boot code must leave room for 8 bytes mock-up of APM Block0)
|
|
APM
|
|
GPT
|
|
|
|
MBR Partitions:
|
|
0xee from 0 to PREP-1, protective partition, announcing presence of GPT
|
|
0x41 from PREP to HFAT-1, PreP partition
|
|
0x0c from HFAT to END-1, FAT partition, bootable bit on
|
|
0x00 Empty partition
|
|
|
|
GPT Partitions:
|
|
The primary GPT itself covers the System Area.
|
|
Basic Data from 16 to EFI-1, protects first part of ISO image
|
|
EFI System from EFI to PREP-1, offers EFI image for booting
|
|
Basic Data from PREP to HFAT-1, protects PreP partition
|
|
HFS+ from HFAT to TAIL-1, offers HFS+ for mounting
|
|
Basic Data from TAIL to GPTB-1, protects rest of ISO image (if there is)
|
|
|
|
APM Partitions:
|
|
The range from end of APM to end of System Area stays unprotected.
|
|
(The primary GPT might sit there.)
|
|
Apple_partition_map from 1 to 3 or 4, covers the APM itself
|
|
ISO9660_data from 16 to HFAT-1, covers first part of ISO image
|
|
Apple_HFS from HFAT to GPTB-1, offers HFS+ for boot and mount
|
|
ISO9660_data from GPTB to END-1, covers rest of ISO image
|
|
(might be omitted if empty)
|
|
|
|
El Torito:
|
|
Boot image for 80x86 PC-BIOS
|
|
Boot image for EFI (usually the same file as the partition EFI to PREP-1).
|
|
|
|
If optional components are not present, then their addresses coincide with
|
|
the address of the next component that is present. E.g. HFAT == DATA if no
|
|
HFS+/FAT filesystem is present.
|
|
If no FAT filesystem is present within HFS+/FAT, then the type of the last
|
|
partition is 0xcd.
|
|
If neither EFI, nor PreP, nor FAT within HFS+/FAT, are present, then there
|
|
is only one partition. It has type 0xee, if GPT is present in the System Area.
|
|
It has type 0xcd and offset 1*512, if no GPT is present.
|
|
|
|
Involved -as mkisofs options:
|
|
-hfsplus
|
|
-fat
|
|
-efi-boot-part DISKFILE
|
|
-prep-boot-part DISKFILE
|
|
|
|
|
|
>>> What boots by what ?
|
|
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|