Updated description of boot sectors by sparse info about PReP, CHRP.

Described the layout for GRUB2 based hybrid images.
This commit is contained in:
Thomas Schmitt 2012-06-12 17:42:22 +02:00
parent 6a3273dc72
commit d7401f0a4c

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@ -17,9 +17,9 @@ EL Torito CD booting, for PC-BIOS x86, PowerPC, (old) Mac, EFI.
Master Boot Record (MBR), for PC-BIOS x86 from (pseudo-) hard disk
Apple Partition Map (APM)
Apple Partition Map (APM), for more modern Mac
GUID Partition Table (GPT)
GUID Partition Table (GPT), for EFI from (pseudo-) hard disk
MIPS Volume Header, for MIPS Big Endian, e.g. SGI Indigo2.
@ -27,10 +27,16 @@ DEC Boot Block, for MIPS Little Endian , e.g. DECstation.
SUN Disk Label and boot images, for SUN SPARC
PowerPC Reference Platform (PReP), for IBM PowerPC
Common Hardware Reference Platform (CHRP), for IBM PowerPC
Combinations of boot mechanisms:
- SYSLINUX isohybrid MBR
- SYSLINUX isohybrid for MBR, UEFI and x86 Mac
- GRUB2 grub-mkrescue MBR
>>> Mac and/or PowerPC bootable GRUB2 image with HFS+/FAT, APM,
EFI GPT partition, PreP MBR partition, mountable FAT partition
------------------------------------------------------------------------------
@ -50,7 +56,13 @@ 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
After the System Area, an ISO 9660 image usually has three distinct block
intervals for:
- Volume descriptors (Primary Volume Descriptor, Boot Record, Joliet, ...)
- Directory trees, tables, boot catalog, embedded partitions and filesystems.
- Data file content, including content of El Torito boot images.
The Boot Record is an 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
@ -373,8 +385,8 @@ HFS+ filesystem.
Block0 of an APM begins at byte 0 of the medium. Thus it collides with MBR and
other boot sector formats. By lucky coincidence it is possible to compose
a mock-up of a Block0 which is acceptable to firmware which expects APM,
and is also harmless x86 machine with no negative side effects.
So it is possible to combine APM with specially prepared MBR.
and is also harmless x86 machine code with no negative side effects.
So it is possible to combine APM with an especially prepared MBR.
The layout of a Block0 of an APM is:
@ -424,6 +436,7 @@ Byte Range | Value | Meaning (all numbers are stored big endian)
| | bit1= entry is allocated
| | bit4= partition is readable
| | bit5= partition is writable
| | 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
@ -457,11 +470,11 @@ start_block = start_of_hfs
block_count = end_of_hfs - start_of_hfs
name = "HFSPLUS_Hybrid"
type = "Apple_HFS"
flags = 0x13
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 forth APM entry will be written.
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"
@ -479,7 +492,7 @@ flags = 0x13
GUID Partition Table (GPT)
for alternative mountability paths
and for booting of some Apple Macs from (pseudo-) hard disk
and for EFI booting of some Apple Macs from (pseudo-) hard disk
Sources:
http://mjg59.dreamwidth.org/11285.html
@ -536,6 +549,7 @@ A globally registered class of GUID are the partition type GUIDs.
This example uses two of them
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-endia interpretation.
@ -581,6 +595,11 @@ Byte Range | Value | Meaning (little endian numbers, LBA unit is 512 byte)
| | 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.
------------------------------------------------------------------------------
@ -866,6 +885,36 @@ Byte Range | Value | Meaning
---------- | ---------- | ----------------------------------------------------
------------------------------------------------------------------------------
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.
CHRP is marked by an MBR partition entry of type 0x96 spanning the whole
ISO 9660 image.
PReP boot may be preferable. At least it can co-exist with other partitions
in the ISO image.
------------------------------------------------------------------------------
>>> ??? HP-PA
@ -1299,9 +1348,73 @@ Vladimir Serbinenko about the partition table entry:
------------------------------------------------------------------------------
>>> Mac bootable GRUB2 image with HFS+ and APM
>>> ? With EFI partition ?
>>> ? With PC-BIOS MBR ?
>>> 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
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