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Described the CRC algorithm of GPT

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This commit is contained in:
Thomas Schmitt 2012-05-07 20:33:53 +02:00
parent dc2b27ca51
commit 977161cda1
1 changed files with 20 additions and 15 deletions
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doc/boot_sectors.txt
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@ -426,15 +426,15 @@ firmware as possible.
1024 - 2047 | unused | 1024 - 2047 | unused |
2048 - 4095 | apm_entry1 | APM entry 1 describing ISO image size. 2048 - 4095 | apm_entry1 | APM entry 1 describing ISO image size.
4096 - 6143 | apm_entry2 | APM entry 2 describing the UEFI VFAT boot image. 4096 - 6143 | apm_entry2 | APM entry 2 describing the UEFI VFAT boot image.
6144 - 8195 | apm_entry3 | APM entry 2 describing the HFS+ 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. 8192 - 8319 | gpt_entry1 | GPT partition entry 1 for the ISO image size.
8320 - 8447 | gpt_entry2 | GPT partition entry 2 for UEFI VFAT boot image, 8320 - 8447 | gpt_entry2 | GPT partition entry 2 for UEFI VFAT boot image,
8448 - 8575 | gpt_entry3 | GPT partition entry 3 for the HFS+ 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. 8576 - 24575 | gtp_empty | Empty GPT partition entries 4 to 128.
24576 - 32767 | unused | 24576 - 32767 | unused |
32768 - 34815 | iso_pvd | ISO 9660 superblock 32768 - 34815 | iso_pvd | ISO 9660 superblock
34815 - 36863 | el_torito | EL Torito boot block pointing to a boot catalog 34816 - 36863 | el_torito | EL Torito boot block pointing to a boot catalog
| | with entries for the MBR boot image (platform | | with entries for the MBR boot image (platform id
| | 0x00), and for the two other boot images | | 0x00), and for the two other boot images
| | (platform id 0xef) | | (platform id 0xef)
-------------- | ---------- | ------------------------------------------------- -------------- | ---------- | -------------------------------------------------
@ -518,18 +518,22 @@ Byte Range | Value | Meaning (little endian numbers, LBA unit is 512 byte)
92 - 511 | reserved | Must be 0 92 - 511 | reserved | Must be 0
---------- | ---------- | ---------------------------------------------------- ---------- | ---------- | ----------------------------------------------------
>>> CRC-32: Generating polynomial 0x104c11db7, mirrored bit order in and out, The CRC-32 algorithm can be characterized as follows:
>>> seed 0xffffffff, result gets exored by 0xffffffff. The generating polynomial has the bit representation 0x104c11db7.
>>> ??? This works as byte shifter with a bitwise mirrored table The seed value for a bit shifting division algorithm is 0x46af6449. It is
>>> ??? but not as simple bit shifter. chosen so that the CRC of 0 bytes of input is 0xffffffff.
>>> ??? Both do match if seed == 0. But not with other seeds. The least significant bits of input bytes get processed first. I.e. bit0 of
>>> ??? An algebraic miracle ? 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 bit mirrored. E.g. bit0 becomes bit31,
bit1 becomes bit30, and so on. Further it gets exored with 0xffffffff.
The ISO image has a size of 332362 blocks of 2K = 1329448 blocks of 512. The ISO image has a size of 332362 blocks of 2K = 1329448 blocks of 512.
Because the block size was announced as 2048, the first Apple partition map Because the block size was announced as 2048, the first Apple partition map
entry is located at byte 0x800. entry is located at byte 0x800 = 2048.
It describes the partition map itself: It describes the partition map itself:
50 4d 00 00 00 00 00 03 00 00 00 01 00 00 00 10 50 4d 00 00 00 00 00 03 00 00 00 01 00 00 00 10
P M P M
@ -569,7 +573,7 @@ Byte Range | Value | Meaning (all numbers are stored big endian)
136 - 511 | reserved | 136 - 511 | reserved |
---------- | ---------- | ---------------------------------------------------- ---------- | ---------- | ----------------------------------------------------
The next Apple partition map entry is at byte 0x1000: 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 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 45 46 49 00 00 00 00 00 00 00 00 00 00 00 00 00
@ -588,7 +592,7 @@ flags = 0x33 : valid, allocated, readable, writable.
This points to file /isolinux/efiboot.img in the ISO image, This points to file /isolinux/efiboot.img in the ISO image,
>>> but misrepresents its size of 284 blocks of 2048. >>> but misrepresents its size of 284 blocks of 2048.
At byte 0x1800, there is map entry 3: At byte 0x1800 = 6144, there is map entry 3:
50 4d 00 00 00 00 00 03 00 00 01 51 00 00 08 c0 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 45 46 49 00 00 00 00 00 00 00 00 00 00 00 00 00
@ -608,7 +612,8 @@ flags = 0x33 : valid, allocated, readable, writable.
>>> GPT partitions marking ISO image, VFAT image within, HFS+ image within >>> GPT partitions marking ISO image, VFAT image within, HFS+ image within
At byte 0x2000 begins the GPT partition array. It ends at byte 0x4000. 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 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 a1 87 a1 ba 4d 2c 27 45 ae 05 cf ab a6 fa 87 c1
@ -641,7 +646,7 @@ Byte Range | Value | Meaning (numbers are stored little endian)
| | >>> of faulty memory operation on a text constant. | | >>> of faulty memory operation on a text constant.
---------- | ---------- | ---------------------------------------------------- ---------- | ---------- | ----------------------------------------------------
Next entry: Next entry is at 0x2800 = 10240:
a2 a0 d0 eb e5 b9 33 44 87 c0 68 b6 b7 26 99 c7 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 c8 de c8 1f fb f0 51 40 8c 8a d2 f6 b1 46 16 dc
@ -658,7 +663,7 @@ Start at block 0xa4 = 164 * 512 = 41 * 2048. The VFAT image file.
Last block is 0x0513 = 1299 = 164 + 1135. This end is correct. Last block is 0x0513 = 1299 = 164 + 1135. This end is correct.
>>> The name is an unintentional patchwork in an 8 bit character set. >>> The name is an unintentional patchwork in an 8 bit character set.
Next entry: Next entry at byte 0x02100 = 8448:
00 53 46 48 00 00 aa 11 aa 11 00 30 65 43 ec ac 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 c8 de c8 1f fb f0 51 40 8c 8a d2 f6 b1 46 16 dc