663 lines
29 KiB
Plaintext
663 lines
29 KiB
Plaintext
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Collection of Boot Sector Formats for ISO 9660 Images
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by Thomas Schmitt - mailto:scdbackup@gmx.net
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Libburnia project - mailto:libburn-hackers@pykix.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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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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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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------------------------------------------------------------------------------
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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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man mkisofs by Joerg Schilling.
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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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The Boot Record is a ECMA-119 Volume Descriptor which is eventually located
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at 2 kB block number 17 (decimal). Its content points to the location of the
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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 refered 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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Further in use by GRUB2 is:
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0xef = EFI, a competitor resp. successor to PC-BIOS, possibly in use with
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Intel ia64 Itanium and possibly with newer Apple machines.
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Words resp. numbers are represented are 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.
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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
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| | 0 for boot_media == 0.
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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.
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| | See above Initial/Default Entry
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| | libisofs stores 1 for emulated boot_media and
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| | 0 for boot_media == 0.
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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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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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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.
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16 - 19 | file_len | Number of bytes in boot image file content.
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20 - 23 | checksum | Little-endian: The sum of all 32-bit words of the
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| | file content from byte 64 to file end.
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24 - 63 | 0 | Reserved
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---------- | ---------- | ----------------------------------------------------
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------------------------------------------------------------------------------
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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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Mailing list conversations with H. Peter Anvin and Vladimir Serbinenko.
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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 eventual MBR comes into effect it the image is on a media that is
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interpreted by the BIOS as some kind of hard disk. Usually real hard disks,
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floppy disks, 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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For C/H/S, the sector address is broken up into whole cylinders, remaining
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heads, and remaining sectors. The nomenclature seems to stem from antique
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drum storage.
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C/H/S counting starts with 0/0/1, not 0/0/0.
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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 it is more or less arbitray how to convert a LBA into
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a C/H/S address and vice versa. For maximum range of C/H/S addresses one
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may use sectors_per_head = 63 , heads_per_cylinder = 255.
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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 of obscure
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| | usability.
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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 | Governs bootability:
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| | 0x80 = bootable/active , 0x00 non-bootable/inactive
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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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| | 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 partiton.
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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) resp. 64 (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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SYSLINUX Isohybrid MBR
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Sources:
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syslinux-3.72/utils/isohybrid , a perl script by H. Peter Anvin = hpa.
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Mailing list conversations with hpa.
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An isohybrid MBR directs the booting BIOS to an ISOLINUX boot image which
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is also the target of an El Torito boot catalog entry.
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For that purpose one has to take an MBR template and has to set a few bytes
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to values which sufficiently describe the ISO image and the boot image file.
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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 - 431 | = opaque = | Syslinux machine code provided by MBR template
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432 - 439 | hd_bootlba | Address of the ISOLINUX boot image file in the
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| | ISO image. Counted in 512 byte blocks.
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440 - 443 | mbr_id | Random number
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444 - 445 | 0 | Padding
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446 - 509 | ========== | Partition table
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446 - 461 | part_entry | Partition table entry 1 describing ISO image size
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| | starting at LBA 0. I.e. contrary to tradition.
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| | See above for partition table entry format.
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462 - 509 | 0 | Unused partition entries 2 to 4
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510 - 511 | 0xaa55 | MBR signature
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---------- | ---------- | ----------------------------------------------------
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hpa about MBR templates and partition table filesystem types:
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"[MBR templates] are available in the Syslinux build tree under the names:
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mbr/isohdp[fp]x*.bin
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The default probably should be mbr/isohdppx.bin, but it's ultimately up
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to the user.
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[...]
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Note: the filesystem type is largely arbitrary, in theory it can be any
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value other than 0x00, 0x05, 0x0f, 0x85, 0xee, or 0xef. 0x17 ("Windows
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IFS Hidden") seems safeish, some people believe 0x83 (Linux) is better.
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"
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------------------------------------------------------------------------------
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GRUB2 grub-mkrescue MBR
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Sources:
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Mailing list conversations with Vladimir Serbinenko.
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The MBR file that is used with GRUB2 script grub-mkrescue needs only a
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partition table entry which describes the image size.
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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0 - 445 | = opaque = | GRUB2 machine code provided by MBR template
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446 - 509 | ========== | Partition table
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446 - 461 | part_entry | Partition table entry 1 describing ISO image size
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| | Peculiar is the start offset of 1 block.
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| | This prevents mounting of the partition.
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| | See above for partition table entry format.
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462 - 509 | 0 | Unused partition entries 2 to 4
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510 - 511 | 0xaa55 | MBR signature
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---------- | ---------- | ----------------------------------------------------
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Vladimir Serbinenko about the partition table entry:
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"Currently we use first and not last entry. You need to:
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1) Zero-fill 446-510
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2) Put 0x55, 0xAA into 510-512
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3) Put 0x80 (for bootable partition), 0, 2, 0 (C/H/S of the start), 0xcd
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(partition type), [3 bytes of C/H/S end], 0x01, 0x00, 0x00, 0x00 (LBA
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start in little endian), [LBA end in little endian] at 446-462
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"
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------------------------------------------------------------------------------
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MIPS Volume Header
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for MIPS Big Endian, e.g. SGI Indigo2
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Sources:
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cdrkit-1.1.10/genisoimage/boot-mips.c
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by Steve McIntyre <steve@einval.com>
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which refers to
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genisovh by Florian Lohoff <flo@rfc822.org>
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and Thiemo Seufer <seufer@csv.ica.uni-stuttgart.de>
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who seem to have learned parameter settings from IRIX CD media
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There are traces in the web which relate this to specs by
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MIPS Computer Systems, Inc. , 1985
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Silicon Graphics Computer Systems, Inc. , 2000
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The first 512 bytes of the media constitute the Volume Header.
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Words are composed big-endian style.
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Byte Range | Value | Meaning
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---------- | ---------- | ----------------------------------------------------
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0 - 3 | 0x0be5a941 | Magic number
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4 - 5 | 0 | Root partition number
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6 - 7 | 0 | Swap partition number
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8 - 23 | 0 | Name of file to boot (unclear what this means)
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| |
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24 - 71 | ========== | Device Parameters
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| |
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24 - 24 | 0 | Spiral addressing skew (unclear what this means)
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25 - 25 | 0 | Words of 0 before header
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26 - 26 | 0 | Words of 0 between hdr and data
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27 - 27 | 0 | Spare sectors per cylinder
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28 - 29 | num_cyl_l | Number of usable cylinder, lower two bytes
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| | ((iso_size + BYTES_PER_SECTOR - 1) /
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| | (SECTORS_PER_TRACK * BYTES_PER_SECTOR)) & 0xffff
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30 - 31 | 0 | Starting head of volume 0
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32 - 33 | 1 | Number of tracks per cylinder
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34 - 34 | 0 | Depth of CTQ queue (unclear what this means)
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35 - 35 | num_cyl_h | Number of usable cylinders, high byte
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| | ((iso_size + BYTES_PER_SECTOR - 1) /
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| | (SECTORS_PER_TRACK * BYTES_PER_SECTOR)) >> 16
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36 - 37 | 0 | unused
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38 - 39 | 32 | SECTORS_PER_TRACK
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40 - 41 | 512 | BYTES_PER_SECTOR
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42 - 43 | 0 | Sector interleave (unclear what this means)
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44 - 47 | 0x00000034 | Controller characteristics composed from
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| | 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 lenght 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
|
|
---------- | ---------- | ----------------------------------------------------
|
|
|
|
Test image produced by
|
|
genisoimage -o /u/test/mips_boot.iso -mips-boot checksum.c jte
|
|
which reports
|
|
Found mips boot image checksum.c, using extent 636 (0x27C), #blocks 14336 (0x3800)
|
|
|
|
xorriso reports as 2048 byte LBA of the boot image dummy file
|
|
File data lba: 0 , 159 , 7 , 14330 , '/CHECKSUM.C'
|
|
|
|
First 512 bytes in hex:
|
|
0 : 0b e5 a9 41 00 00 00 00 00 00 00 00 00 00 00 00
|
|
16 : 00 00 00 00 00 00 00 00 00 00 00 00 00 51 00 00
|
|
32 : 00 01 00 00 00 00 00 20 02 00 00 00 00 00 00 34
|
|
48 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
64 : 00 00 00 00 00 00 00 00 63 68 65 63 6b 73 75 6d
|
|
80 : 00 00 02 7c 00 00 38 00 00 00 00 00 00 00 00 00
|
|
... 0 ...
|
|
400 : 00 00 00 00 00 00 00 00 00 00 0a 28 00 00 00 00
|
|
416 : 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
|
|
432 : 00 00 0a 28 00 00 00 00 00 00 00 06 00 00 00 00
|
|
... 0 ...
|
|
496 : 00 00 00 00 00 00 00 00 22 ec 2c c9 00 00 00 00
|
|
|
|
The 32 bit two's complement of bytes 0 to 503 is 0x22ec2cc9.
|
|
|
|
In decimal:
|
|
0 : 11 229 169 65 0 0 0 0 0 0 0 0 0 0 0 0
|
|
16 : 0 0 0 0 0 0 0 0 0 0 0 0 0 81 0 0
|
|
32 : 0 1 0 0 0 0 0 32 2 0 0 0 0 0 0 52
|
|
48 : 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
|
|
64 : 0 0 0 0 0 0 0 0 99 104 101 99 107 115 117 109
|
|
80 : 0 0 2 124 0 0 56 0 0 0 0 0 0 0 0 0
|
|
... 0 ...
|
|
400 : 0 0 0 0 0 0 0 0 0 0 10 40 0 0 0 0
|
|
416 : 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
|
|
432 : 0 0 10 40 0 0 0 0 0 0 0 6 0 0 0 0
|
|
... 0 ...
|
|
496 : 0 0 0 0 0 0 0 0 34 236 44 201 0 0 0 0
|
|
|
|
Cleartext part:
|
|
64 : c h e c k s u m
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
|
|
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
|
|
| | + 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
|
|
| |
|
|
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
>>> ??? HP-PA
|
|
|
|
------------------------------------------------------------------------------
|
|
|
|
>>> ??? DEC Alpha
|
|
|
|
------------------------------------------------------------------------------
|
|
|