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Described El Torito, grub-mkrescue MBR, MIPS Little Endian booting.

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Thomas Schmitt 2010-10-14 17:26:56 +02:00
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doc/boot_sectors.txt
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@ -8,38 +8,268 @@
Libburnia project - mailto:libburn-hackers@pykix.org
This information is collected from various sources. Some is backed by
specifications, some is just rumor which happens to work.
specifications, some is just rumor which happens to work (maybe not even that).
Content
EL Torito CD booting, for PC-BIOS x86, PowerPC, (old) Mac, EFI.
MBR, for PC-BIOS x86 from (pseudo-) hard disk
- SYSLINUX Isohybrid MBR
- GRUB2 grub-mkrescue MBR.
MIPS Volume Header, for MIPS Big Endian, e.g. SGI Indigo2.
------------------------------------------------------------------------------
>>> EL Torito
EL Torito CD booting
for PC-BIOS x86, PowerPC, (old) Mac, EFI
El Torito, Bootable CD-ROM Format Specification, Version 1.0, January 25, 1995
Sources:
El Torito, Bootable CD-ROM Format Specification, Version 1.0, 1995
which refers to ECMA-119, the standard for ISO 9660 filesystems.
libisofs/eltorito.[ch] by Vreixo Formoso.
man mkisofs by Joerg Schilling.
>>> El Torito Volume Descriptor
>>> Boot Catalog
ECMA-119 prescribes that the first 32 kB of an ISO 9660 image are System Area
with arbitrary content. This prescription is obeyed by PC-BIOS systems only
if the ISO 9660 image is presented on CD, DVD or BD media.
In this case the El Torito Boot record is the starting point of booting.
The Boot Record is a ECMA-119 Volume Descriptor which is eventually located
at 2 kB block number 17 (decimal). Its content points to the location of the
Boot Catalog.
The format is described in part by ECMA-119 8.2 "Boot Record" and further
specified by El Torito figure 7.
Byte Range | Value | Meaning
---------- | ---------- | ----------------------------------------------------
0 - 0 | 0 | Volume Descriptor Type. 0= Boot record
1 - 5 | "CD001" | Standard Identifier
6 - 6 | 1 | Volume Descriptor Version
7 - 38 | el_torito | Boot System Identifier
39 - 70 | 0 | Boot Identifier
| |
71 -2047 | ========== | Boot System Use
| |
71 - 74 | cataloglba | The 2 kB block number of the Boot Catalog
| | as little-endian 32 bit number.
| |
75 -2047 | 0 | Unused
---------- | ---------- | ----------------------------------------------------
el_torito is the constant string "EL TORITO SPECIFICATION" padded by 9 zeros.
cataloglba has to be provided by the file system generator.
The Boot Catalog lists the available boot images which may be prepared for
multiple system architectures, called "platforms".
It consists of one or more 2 kB blocks. The content is a sequence of fixed
format entries, 32 bytes each.
The entries are grouped in sections, which assign the entries to a particular
system architecture. The booting system will then choose an entry from an
appropriate section.
Byte Range | Value | Meaning
---------- | ---------- | ----------------------------------------------------
0 - 31 | ========== | Validation Entry
| | begins the first section, specifies an architecture
32 - 63 | ========== | Initial/Default Entry
| | points to a boot image for given architecture
---------- | ---------- | ----------------------------------------------------
Optional:
---------- | ---------- | ----------------------------------------------------
64 - 95 | ========== | Section Header entry
| | begins new section, specifies an architecture
96 - 127 | ========== | Section Entry
| | points to a boot image for given architecture
... | .......... | Optional more Section Entries
... | .......... | Optional more Section Headers and their Section
| | Entries
---------- | ---------- | ----------------------------------------------------
An architecture is refered by a Platform Id number.
Defined by El Torito are:
0 = "80x86" which is used for standard PCs with Intel x86 or compatible CPU
1 = "PowerPC" (possibly for IBM machines with PowerPC CPU)
2 = "Mac" (possibly for Apple computers with MC68000 or PowerPC CPU)
Further in use by GRUB2 is:
0xef = EFI, a competitor resp. successor to PC-BIOS, possibly in use with
Intel ia64 Itanium and possibly with newer Apple machines.
Words resp. numbers are represented are little-endian.
Validation Entry:
Byte Range | Value | Meaning
---------- | ---------- | ----------------------------------------------------
0 - 0 | 1 | Header Id
| |
1 - 1 | platform_id| Platform Id. One of: 0, 1, 2, 0xef. See above.
| |
2 - 3 | 0 | Reserved
4 - 27 | manuf_dev | ID string identifies the manufacturer/developer
| | (no non-zero examples known yet)
| |
28 - 29 | checksum | Checksum Word for the Validation Entry.
| | The sum of all words in the entry has to be 0.
| |
30 - 30 | 0x55 |
31 - 31 | 0xaa |
---------- | ---------- | ----------------------------------------------------
Initial/Default Entry:
Byte Range | Value | Meaning
---------- | ---------- | ----------------------------------------------------
0 - 0 | boot_indct | Boot Indicator: 0x88 = bootable, 0x00 = not bootable
| |
1 - 1 | boot_media | Boot Media Type (i.e. media emulated by boot image):
| | 0= no emulation , 1= 1.2 MB diskette, 2=1.44 MB,
| | 3= 2.88 MB , 4= hard disk
| | (About everybody uses 0 = no emulation)
| |
2 - 3 | load_seg | Load Segment. (meaning unclear)
| | "If this value is 0 the system will use the
| | traditional segment of 7C0."
| | libisofs default is 0
| |
4 - 4 | sys_type | System Type.
| | "Must be a copy of byte 5 from the partition table
| | found in the boot image."
| | libisofs reads the start the boot image as MBR
| | if boot_media == 4. This emulated MBR has a
| | partition table from where a byte gets copied.
| | Else this byte is 0.
| |
5 - 5 | 0 | Unused
| |
6 - 7 | sec_count | Sector Count.
| | "the number of virtual/emulated sectors the system
| | will store at Load Segment during the initial boot
| | procedure."
| | libisofs stores 1 for emulated boot_media and
| | 0 for boot_media == 0.
| |
8 - 11 | load_rba | Load RBA. The 2 kB block address where the boot
| | image file content is located in the ISO 9660 image.
| |
12 - 31 | 0 | Unused
---------- | ---------- | ----------------------------------------------------
Section Header Entry:
Byte Range | Value | Meaning
---------- | ---------- | ----------------------------------------------------
0 - 0 | head_ind | Header Indicator: 0x90 = more headers follow
| | 0x91 = final header, last section
| |
1 - 1 | platform_id| Platform Id. One of: 0, 1, 2, 0xef. See above.
| |
2 - 3 | num_entries| Number of entries to follow in this section
| |
4 - 31 | | ID string identifies the manufacturer/developer
---------- | ---------- | ----------------------------------------------------
Section Entry:
Byte Range | Value | Meaning
---------- | ---------- | ----------------------------------------------------
0 - 0 | boot_indct | Boot Indicator: 0x88 = bootable, 0x00 = not bootable
| |
1 - 1 | boot_media | Boot Media Type (i.e. media emulated by boot image):
| | Bit 0 to 3 govern emulation
| | 0= no emulation , 1= 1.2 MB diskette, 2=1.44 MB,
| | 3= 2.88 MB , 4= hard disk
| | (About everybody uses 0 = no emulation)
| | Bit 4 is reserved and must be 0
| | Bit 5 "Continuation entry follows" (meaning unclear)
| | Might be the indicator for Extension Entries,
| | which are not described here.
| | Bit 6 "Image contains an ATAPI driver"
| | Bit 7 "Image contains SCSI drivers"
| |
2 - 3 | load_seg | Load Segment. (meaning unclear)
| | See above Initial/Default Entry
| | libisofs default is 0.
4 - 4 | sys_type | System Type.
| | See above Initial/Default Entry
| | 0 if not emulation == 4.
5 - 5 | 0 | Unused
| |
6 - 7 | sec_count | Sector Count.
| | See above Initial/Default Entry
| | libisofs stores 1 for emulated boot_media and
| | 0 for boot_media == 0.
| |
8 - 11 | load_rba | Load RBA. The 2 kB block address where the boot
| | image file content is located in the ISO 9660 image.
| |
12 - 31 | sel_crit | "Vendor unique selection criteria."
---------- | ---------- | ----------------------------------------------------
The boot image file content is mostly opaque to the ISO 9660 image generator.
Nevertheless there is a tradition named "Boot Info Table" which prescribes
to write information into byte fields of the boot image file content.
There are no general means known how a producer of ISO 9660 images could
detect the need for Boot Info Table production.
It rather needs a hint from the user who has to know whether the boot image
expects a Boot Info Table.
The Boot Info Table begins at byte 8 of the boot image content.
Byte Range | Value | Meaning
---------- | ---------- | ----------------------------------------------------
8 - 11 | pvd_lba | Block address of the Primary Volume Descriptor
| | This is the session start LBA + 16.
| |
12 - 15 | file_lba | Block address of the start of the boot image file
| | content.
| |
16 - 19 | file_len | Number of bytes in boot image file content.
| |
20 - 23 | checksum | Little-endian: The sum of all 32-bit words of the
| | file content from byte 64 to file end.
| |
24 - 63 | 0 | Reserved
---------- | ---------- | ----------------------------------------------------
>>> Boot Images
------------------------------------------------------------------------------
>>> MBR
MBR
for PC-BIOS x86 from (pseudo-) hard disk
Sources:
http://en.wikipedia.org/wiki/Master_boot_record
The candidates for MBR booting will normally use El Torito rather than MBR
if the ISO image is presented on CD, DVD, or BD media.
The eventual MBR comes into effect it the image is on a media that is
interpreted by the BIOS as some kind of hard disk. Usually real hard disks,
floppy disks, USB sticks, memory cards.
>>>
>>> iso_write_opts_set_part_offset()
------------------------------------------------------------------------------
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
@ -50,7 +280,6 @@ 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
@ -61,29 +290,56 @@ Byte Range | Value | Meaning
446 - 461 | part_entry | Partition table entry 1 describing ISO image size
| |
462 - 509 | 0 | Unused partition entries 2 to 4
| |
510 - 511 | 0xaa55 | MBR signature
---------- | ---------- | ----------------------------------------------------
hpa about MBR templates and partition table filesystem types:
-------------------------------------------------------------
[MBR templates] are available in the Syslinux build tree under the names:
"[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.
"
------------------------------------------------------------------------------
>>> GRUB2 MBR
GRUB2 grub-mkrescue MBR
Sources:
Mailing list conversations with Vladimir Serbinenko.
The MBR file that is used with GRUB2 script grub-mkrescue needs only a
partition table entry which describes the image size.
Byte Range | Value | Meaning
---------- | ---------- | ----------------------------------------------------
0 - 445 | = opaque = | GRUB2 machine code 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.
| |
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
"
------------------------------------------------------------------------------
@ -224,7 +480,84 @@ Cleartext part:
------------------------------------------------------------------------------
>>> MIPSEL Little Endian MIPS , e.g. DECstation
MIPSEL Little Endian MIPS , 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.
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 | count | Segment size in file.
| | Stems from ELF header of boot file.
| | (Elf32_Phdr field p_filesz + 511) / 512;
| |
28 - 31 | start | Segment file offset
| | 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 */
| -> start | Needed for start
| |
8 - 11 | p_vaddr | /* Segment virtual address */
=load_address| Needed for load_address
| |
12 - 15 | | (Segment physical address)
| |
16 - 19 | p_filesz | /* Segment size in file */
| -> count | Needed for count
| |
------------------------------------------------------------------------------

4
libisofs/libisofs.h
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@ -1768,11 +1768,13 @@ int iso_write_opts_set_fifo_size(IsoWriteOpts *opts, size_t fifo_size);
* only if not bit0 is set.
* bit2-7= System area type
* 0= with bit0 or bit1: MBR
* else: unspecified type
* else: unspecified type which will be used unaltered.
* @since 0.6.38
* 1= MIPS Big Endian Volume Header
* Submit up to 15 MIPS Big Endian boot files by
* iso_image_add_mips_boot_file().
* This will overwrite the first 512 bytes of the submitted
* data.
* @param flag
* bit0 = invalidate any attached system area data. Same as data == NULL
* (This re-activates eventually loaded image System Area data.