EBR：扩展分区和逻辑分区

扩展分区和逻辑分区之关系

由于MBR里磁盘分区结构只有64字节的空间可用，而每个分区项需要16个字节，因此，MBR里最多只能存储4个分区。这就是为什么会有扩展分区和逻辑分区的原因：在一块磁盘上不受限于只能有4个分区，可以按需制作多个分区。那么，扩展分区是怎么实现的呢？

扩展分区和逻辑分区的关系，可以用下图表示，其中绿色块代表的是2048块扇区。很明显，每个逻辑分区前面都有2048块没有使用的扇区

逻辑分区的分区数据，就存储在这些没有使用的扇区里，准确的说，是储存在其中的第一个扇区里（这个扇区叫做扩展引导扇区，简称EBR）。虽然EBR使用和MBR一样的分区表结构。但是，不同于MBR分区表，每个EBR分区表都只是使用前两项记录。一项记录当前的逻辑分区，一项记录下一个逻辑分区。这样，EBR数据之间就构成了一个树结构，可以任意扩展

当然，这也意味着每个逻辑分区，除了第一个逻辑分区外，都是有两条分区数据的。有趣的是，这两条记录并不完全一样。

让我们综合一下。从MBR分区数据我们能够确定扩展分区，然后根据扩展分区，我们可以确定逻辑分区

验证

我们使用如下的数据来验证扩展分区和逻辑分区以及其间之关系

我们首先验证每个逻辑分区前都有2048块空闲扇区

接下来我们验证这些空闲的2048块扇区的第一块扇区里都有两个分区数据。当然，最后一块逻辑分区例外

一个逻辑分区的两条记录并不一致

我们验证一下fdisk的输出和磁盘MBR和EBR记录之间的关系

用到的命令

dd if=/dev/sdb bs=1 count=64 skip=446 2>/dev/null | od -v -tx1for n in 14336 4210688 8407040;do \fisrt_sector_number=$(expr $n - 2048);\dd if=/dev/sdb bs=1 count=64 skip=$(expr ${fisrt_sector_number} \* 512 + 446) 2>/dev/null | \od -v -tx1;\done{dd if=/dev/sdb bs=1 count=64 skip=446 2>/dev/null | od -v -tx1;\for n in 14336 4210688 8407040;do \fisrt_sector_number=$(expr $n - 2048);\dd if=/dev/sdb bs=1 count=64 skip=$(expr ${fisrt_sector_number} \* 512 + 446) 2>/dev/null | \od -v -tx1;\done} | \perl -nE 'chomp;print qq[$_ ];if (/\s[0-9a-f]+\s*/) { @fields = split; print hex(qq{$fields[11]$fields[10]$fields[9]$fileds[8]});}print qq[\n];'

LVM：又一层包装

我们直接给出LVM的实际例子，供大家自行分析如下信息

物理卷

卷组

逻辑卷

很明显，LVM有关的数据结构和关系都是记录在磁盘上的。

## LVM分区信息

[root@localhost ~]# cat lvm.info--- Physical volume ---PV Name /dev/vda5VG Name ubuntuPV Size 9.76 GiB / not usable 2.00 MiBAllocatable yes (but full)PE Size 4.00 MiBTotal PE 2498Free PE 0Allocated PE 2498PV UUID AIie9r-pdTS-09Za-cATW-UC6j-n3lO-4rraGc--- Volume group ---VG Name ubuntuSystem IDFormat lvm2Metadata Areas 1Metadata Sequence No 3VG Access read/writeVG Status resizableMAX LV 0Cur LV 2Open LV 2Max PV 0Cur PV 1Act PV 1VG Size 9.76 GiBPE Size 4.00 MiBTotal PE 2498Alloc PE / Size 2498 / 9.76 GiBFree PE / Size 0 / 0VG UUID padOl1-EPWN-At1M-3GJk-MgFR-mPic-GATrFp--- Logical volume ---LV Name /dev/ubuntu/rootVG Name ubuntuLV UUID qjonzd-yqJh-cLi1-KZvh-0x6H-W9zB-Fy26IcLV Write Access read/writeLV Status available# open 1LV Size 9.29 GiBCurrent LE 2379Segments 1Allocation inheritRead ahead sectors auto- currently set to 256Block device 251:0--- Logical volume ---LV Name /dev/ubuntu/swap_1VG Name ubuntuLV UUID HiLDjt-0TVl-zNj2-QxIM-Vl7m-Upsd-NyfcjwLV Write Access read/writeLV Status available# open 1LV Size 476.00 MiBCurrent LE 119Segments 1Allocation inheritRead ahead sectors auto- currently set to 256Block device 251:1[root@iZ2ze3shz9b6z00qqhjoyzZ ~]#

## 二进制编辑器里的LVM信息

00000000: 4c41 4245 4c4f 4e45 0100 0000 0000 0000 LABELONE........00000010: 9ebe 7a39 2000 0000 4c56 4d32 2030 3031 ..z9 ...LVM2 00100000020: 4149 6965 3972 7064 5453 3039 5a61 6341 AIie9rpdTS09ZacA00000030: 5457 5543 366a 6e33 6c4f 3472 7261 4763 TWUC6jn3lO4rraGc00000040: 0000 a070 0200 0000 0000 0300 0000 0000 ...p...............00000e00: 1a37 8d62 204c 564d 3220 785b 3541 2572 .7.b LVM2 x[5A%r00000e10: 304e 2a3e 0100 0000 0010 0000 0000 0000 0N*>............00000e20: 00f0 0200 0000 0000 000a 0000 0000 0000 ................00000e30: 8e04 0000 0000 0000 c279 ed59 0000 0000 .........y.Y....00000e40: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000e50: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000e60: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000e70: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000e80: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000e90: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000ea0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000eb0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000ec0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000ed0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000ee0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000ef0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f00: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f10: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f20: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f30: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f40: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f50: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f60: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f70: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f80: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000f90: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000fa0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000fb0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000fc0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000fd0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000fe0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00000ff0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001000: 7562 756e 7475 207b 0a69 6420 3d20 2270 ubuntu {.id = "p00001010: 6164 4f6c 312d 4550 574e 2d41 7431 4d2d adOl1-EPWN-At1M-00001020: 3347 4a6b 2d4d 6746 522d 6d50 6963 2d47 3GJk-MgFR-mPic-G00001030: 4154 7246 7022 0a73 6571 6e6f 203d 2031 ATrFp".seqno = 100001040: 0a73 7461 7475 7320 3d20 5b22 5245 5349 .status = ["RESI00001050: 5a45 4142 4c45 222c 2022 5245 4144 222c ZEABLE", "READ",00001060: 2022 5752 4954 4522 5d0a 666c 6167 7320 "WRITE"].flags00001070: 3d20 5b5d 0a65 7874 656e 745f 7369 7a65 = [].extent_size00001080: 203d 2038 3139 320a 6d61 785f 6c76 203d = 8192.max_lv =00001090: 2030 0a6d 6178 5f70 7620 3d20 300a 0a70 0.max_pv = 0..p000010a0: 6879 7369 6361 6c5f 766f 6c75 6d65 7320 hysical_volumes000010b0: 7b0a 0a70 7630 207b 0a69 6420 3d20 2241 {..pv0 {.id = "A000010c0: 4969 6539 722d 7064 5453 2d30 395a 612d Iie9r-pdTS-09Za-000010d0: 6341 5457 2d55 4336 6a2d 6e33 6c4f 2d34 cATW-UC6j-n3lO-4000010e0: 7272 6147 6322 0a64 6576 6963 6520 3d20 rraGc".device =000010f0: 222f 6465 762f 7364 6135 220a 0a73 7461 "/dev/sda5"..sta00001100: 7475 7320 3d20 5b22 414c 4c4f 4341 5441 tus = ["ALLOCATA00001110: 424c 4522 5d0a 666c 6167 7320 3d20 5b5d BLE"].flags = []00001120: 0a64 6576 5f73 697a 6520 3d20 3230 3436 .dev_size = 204600001130: 3737 3132 0a70 655f 7374 6172 7420 3d20 7712.pe_start =00001140: 3338 340a 7065 5f63 6f75 6e74 203d 2032 384.pe_count = 200001150: 3439 380a 7d0a 7d0a 0a7d 0a23 2047 656e 498.}.}..}.# Gen00001160: 6572 6174 6564 2062 7920 4c56 4d32 2076 erated by LVM2 v00001170: 6572 7369 6f6e 2032 2e30 322e 3534 2831 ersion 2.02.54(100001180: 2920 2832 3030 392d 3130 2d32 3629 3a20 ) (2009-10-26):00001190: 4d6f 6e20 4170 7220 3234 2030 383a 3534 Mon Apr 24 08:54000011a0: 3a31 3920 3230 3137 0a0a 636f 6e74 656e :19 2017..conten000011b0: 7473 203d 2022 5465 7874 2046 6f72 6d61 ts = "Text Forma000011c0: 7420 566f 6c75 6d65 2047 726f 7570 220a t Volume Group".000011d0: 7665 7273 696f 6e20 3d20 310a 0a64 6573 version = 1..des000011e0: 6372 6970 7469 6f6e 203d 2022 220a 0a63 cription = ""..c000011f0: 7265 6174 696f 6e5f 686f 7374 203d 2022 reation_host = "00001200: 7562 756e 7475 2209 2320 4c69 6e75 7820 ubuntu".# Linux00001210: 7562 756e 7475 2032 2e36 2e33 322d 3231 ubuntu 2.6.32-2100001220: 2d67 656e 6572 6963 2023 3332 2d55 6275 -generic #32-Ubu00001230: 6e74 7520 534d 5020 4672 6920 4170 7220 ntu SMP Fri Apr00001240: 3136 2030 383a 3130 3a30 3220 5554 4320 16 08:10:02 UTC00001250: 3230 3130 2069 3638 360a 6372 6561 7469 2010 i686.creati00001260: 6f6e 5f74 696d 6520 3d20 3134 3933 3032 on_time = 14930200001270: 3430 3539 0923 204d 6f6e 2041 7072 2032 4059.# Mon Apr 200001280: 3420 3038 3a35 343a 3139 2032 3031 370a 4 08:54:19 2017.00001290: 0a00 0000 0000 0000 0000 0000 0000 0000 ...................00001400: 7562 756e 7475 207b 0a69 6420 3d20 2270 ubuntu {.id = "p00001410: 6164 4f6c 312d 4550 574e 2d41 7431 4d2d adOl1-EPWN-At1M-00001420: 3347 4a6b 2d4d 6746 522d 6d50 6963 2d47 3GJk-MgFR-mPic-G00001430: 4154 7246 7022 0a73 6571 6e6f 203d 2032 ATrFp".seqno = 200001440: 0a73 7461 7475 7320 3d20 5b22 5245 5349 .status = ["RESI00001450: 5a45 4142 4c45 222c 2022 5245 4144 222c ZEABLE", "READ",00001460: 2022 5752 4954 4522 5d0a 666c 6167 7320 "WRITE"].flags00001470: 3d20 5b5d 0a65 7874 656e 745f 7369 7a65 = [].extent_size00001480: 203d 2038 3139 320a 6d61 785f 6c76 203d = 8192.max_lv =00001490: 2030 0a6d 6178 5f70 7620 3d20 300a 0a70 0.max_pv = 0..p000014a0: 6879 7369 6361 6c5f 766f 6c75 6d65 7320 hysical_volumes000014b0: 7b0a 0a70 7630 207b 0a69 6420 3d20 2241 {..pv0 {.id = "A000014c0: 4969 6539 722d 7064 5453 2d30 395a 612d Iie9r-pdTS-09Za-000014d0: 6341 5457 2d55 4336 6a2d 6e33 6c4f 2d34 cATW-UC6j-n3lO-4000014e0: 7272 6147 6322 0a64 6576 6963 6520 3d20 rraGc".device =000014f0: 222f 6465 762f 7364 6135 220a 0a73 7461 "/dev/sda5"..sta00001500: 7475 7320 3d20 5b22 414c 4c4f 4341 5441 tus = ["ALLOCATA00001510: 424c 4522 5d0a 666c 6167 7320 3d20 5b5d BLE"].flags = []00001520: 0a64 6576 5f73 697a 6520 3d20 3230 3436 .dev_size = 204600001530: 3737 3132 0a70 655f 7374 6172 7420 3d20 7712.pe_start =00001540: 3338 340a 7065 5f63 6f75 6e74 203d 2032 384.pe_count = 200001550: 3439 380a 7d0a 7d0a 0a6c 6f67 6963 616c 498.}.}..logical00001560: 5f76 6f6c 756d 6573 207b 0a0a 726f 6f74 _volumes {..root00001570: 207b 0a69 6420 3d20 2271 6a6f 6e7a 642d {.id = "qjonzd-00001580: 7971 4a68 2d63 4c69 312d 4b5a 7668 2d30 yqJh-cLi1-KZvh-000001590: 7836 482d 5739 7a42 2d46 7932 3649 6322 x6H-W9zB-Fy26Ic"000015a0: 0a73 7461 7475 7320 3d20 5b22 5245 4144 .status = ["READ000015b0: 222c 2022 5752 4954 4522 2c20 2256 4953 ", "WRITE", "VIS000015c0: 4942 4c45 225d 0a66 6c61 6773 203d 205b IBLE"].flags = [000015d0: 5d0a 7365 676d 656e 745f 636f 756e 7420 ].segment_count000015e0: 3d20 310a 0a73 6567 6d65 6e74 3120 7b0a = 1..segment1 {.000015f0: 7374 6172 745f 6578 7465 6e74 203d 2030 start_extent = 000001600: 0a65 7874 656e 745f 636f 756e 7420 3d20 .extent_count =00001610: 3233 3739 0a0a 7479 7065 203d 2022 7374 2379..type = "st00001620: 7269 7065 6422 0a73 7472 6970 655f 636f riped".stripe_co00001630: 756e 7420 3d20 3109 2320 6c69 6e65 6172 unt = 1.# linear00001640: 0a0a 7374 7269 7065 7320 3d20 5b0a 2270 ..stripes = [."p00001650: 7630 222c 2030 0a5d 0a7d 0a7d 0a7d 0a7d v0", 0.].}.}.}.}00001660: 0a23 2047 656e 6572 6174 6564 2062 7920 .# Generated by00001670: 4c56 4d32 2076 6572 7369 6f6e 2032 2e30 LVM2 version 2.000001680: 322e 3534 2831 2920 2832 3030 392d 3130 2.54(1) (2009-1000001690: 2d32 3629 3a20 4d6f 6e20 4170 7220 3234 -26): Mon Apr 24000016a0: 2030 383a 3534 3a32 3120 3230 3137 0a0a 08:54:21 2017..000016b0: 636f 6e74 656e 7473 203d 2022 5465 7874 contents = "Text000016c0: 2046 6f72 6d61 7420 566f 6c75 6d65 2047 Format Volume G000016d0: 726f 7570 220a 7665 7273 696f 6e20 3d20 roup".version =000016e0: 310a 0a64 6573 6372 6970 7469 6f6e 203d 1..description =000016f0: 2022 220a 0a63 7265 6174 696f 6e5f 686f ""..creation_ho00001700: 7374 203d 2022 7562 756e 7475 2209 2320 st = "ubuntu".#00001710: 4c69 6e75 7820 7562 756e 7475 2032 2e36 Linux ubuntu 2.600001720: 2e33 322d 3231 2d67 656e 6572 6963 2023 .32-21-generic #00001730: 3332 2d55 6275 6e74 7520 534d 5020 4672 32-Ubuntu SMP Fr00001740: 6920 4170 7220 3136 2030 383a 3130 3a30 i Apr 16 08:10:000001750: 3220 5554 4320 3230 3130 2069 3638 360a 2 UTC 2010 i686.00001760: 6372 6561 7469 6f6e 5f74 696d 6520 3d20 creation_time =00001770: 3134 3933 3032 3430 3631 0923 204d 6f6e 1493024061.# Mon00001780: 2041 7072 2032 3420 3038 3a35 343a 3231 Apr 24 08:54:2100001790: 2032 3031 370a 0a00 0000 0000 0000 0000 2017...........000017a0: 0000 0000 0000 0000 0000 0000 0000 0000 ................000017b0: 0000 0000 0000 0000 0000 0000 0000 0000 ................000017c0: 0000 0000 0000 0000 0000 0000 0000 0000 ................000017d0: 0000 0000 0000 0000 0000 0000 0000 0000 ................000017e0: 0000 0000 0000 0000 0000 0000 0000 0000 ................000017f0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001800: 7562 756e 7475 207b 0a69 6420 3d20 2270 ubuntu {.id = "p00001810: 6164 4f6c 312d 4550 574e 2d41 7431 4d2d adOl1-EPWN-At1M-00001820: 3347 4a6b 2d4d 6746 522d 6d50 6963 2d47 3GJk-MgFR-mPic-G00001830: 4154 7246 7022 0a73 6571 6e6f 203d 2033 ATrFp".seqno = 300001840: 0a73 7461 7475 7320 3d20 5b22 5245 5349 .status = ["RESI00001850: 5a45 4142 4c45 222c 2022 5245 4144 222c ZEABLE", "READ",00001860: 2022 5752 4954 4522 5d0a 666c 6167 7320 "WRITE"].flags00001870: 3d20 5b5d 0a65 7874 656e 745f 7369 7a65 = [].extent_size00001880: 203d 2038 3139 320a 6d61 785f 6c76 203d = 8192.max_lv =00001890: 2030 0a6d 6178 5f70 7620 3d20 300a 0a70 0.max_pv = 0..p000018a0: 6879 7369 6361 6c5f 766f 6c75 6d65 7320 hysical_volumes000018b0: 7b0a 0a70 7630 207b 0a69 6420 3d20 2241 {..pv0 {.id = "A000018c0: 4969 6539 722d 7064 5453 2d30 395a 612d Iie9r-pdTS-09Za-000018d0: 6341 5457 2d55 4336 6a2d 6e33 6c4f 2d34 cATW-UC6j-n3lO-4000018e0: 7272 6147 6322 0a64 6576 6963 6520 3d20 rraGc".device =000018f0: 222f 6465 762f 7364 6135 220a 0a73 7461 "/dev/sda5"..sta00001900: 7475 7320 3d20 5b22 414c 4c4f 4341 5441 tus = ["ALLOCATA00001910: 424c 4522 5d0a 666c 6167 7320 3d20 5b5d BLE"].flags = []00001920: 0a64 6576 5f73 697a 6520 3d20 3230 3436 .dev_size = 204600001930: 3737 3132 0a70 655f 7374 6172 7420 3d20 7712.pe_start =00001940: 3338 340a 7065 5f63 6f75 6e74 203d 2032 384.pe_count = 200001950: 3439 380a 7d0a 7d0a 0a6c 6f67 6963 616c 498.}.}..logical00001960: 5f76 6f6c 756d 6573 207b 0a0a 726f 6f74 _volumes {..root00001970: 207b 0a69 6420 3d20 2271 6a6f 6e7a 642d {.id = "qjonzd-00001980: 7971 4a68 2d63 4c69 312d 4b5a 7668 2d30 yqJh-cLi1-KZvh-000001990: 7836 482d 5739 7a42 2d46 7932 3649 6322 x6H-W9zB-Fy26Ic"000019a0: 0a73 7461 7475 7320 3d20 5b22 5245 4144 .status = ["READ000019b0: 222c 2022 5752 4954 4522 2c20 2256 4953 ", "WRITE", "VIS000019c0: 4942 4c45 225d 0a66 6c61 6773 203d 205b IBLE"].flags = [000019d0: 5d0a 7365 676d 656e 745f 636f 756e 7420 ].segment_count000019e0: 3d20 310a 0a73 6567 6d65 6e74 3120 7b0a = 1..segment1 {.000019f0: 7374 6172 745f 6578 7465 6e74 203d 2030 start_extent = 000001a00: 0a65 7874 656e 745f 636f 756e 7420 3d20 .extent_count =00001a10: 3233 3739 0a0a 7479 7065 203d 2022 7374 2379..type = "st00001a20: 7269 7065 6422 0a73 7472 6970 655f 636f riped".stripe_co00001a30: 756e 7420 3d20 3109 2320 6c69 6e65 6172 unt = 1.# linear00001a40: 0a0a 7374 7269 7065 7320 3d20 5b0a 2270 ..stripes = [."p00001a50: 7630 222c 2030 0a5d 0a7d 0a7d 0a0a 7377 v0", 0.].}.}..sw00001a60: 6170 5f31 207b 0a69 6420 3d20 2248 694c ap_1 {.id = "HiL00001a70: 446a 742d 3054 566c 2d7a 4e6a 322d 5178 Djt-0TVl-zNj2-Qx00001a80: 494d 2d56 6c37 6d2d 5570 7364 2d4e 7966 IM-Vl7m-Upsd-Nyf00001a90: 636a 7722 0a73 7461 7475 7320 3d20 5b22 cjw".status = ["00001aa0: 5245 4144 222c 2022 5752 4954 4522 2c20 READ", "WRITE",00001ab0: 2256 4953 4942 4c45 225d 0a66 6c61 6773 "VISIBLE"].flags00001ac0: 203d 205b 5d0a 7365 676d 656e 745f 636f = [].segment_co00001ad0: 756e 7420 3d20 310a 0a73 6567 6d65 6e74 unt = 1..segment00001ae0: 3120 7b0a 7374 6172 745f 6578 7465 6e74 1 {.start_extent00001af0: 203d 2030 0a65 7874 656e 745f 636f 756e = 0.extent_coun00001b00: 7420 3d20 3131 390a 0a74 7970 6520 3d20 t = 119..type =00001b10: 2273 7472 6970 6564 220a 7374 7269 7065 "striped".stripe00001b20: 5f63 6f75 6e74 203d 2031 0923 206c 696e _count = 1.# lin00001b30: 6561 720a 0a73 7472 6970 6573 203d 205b ear..stripes = [00001b40: 0a22 7076 3022 2c20 3233 3739 0a5d 0a7d ."pv0", 2379.].}00001b50: 0a7d 0a7d 0a7d 0a23 2047 656e 6572 6174 .}.}.}.# Generat00001b60: 6564 2062 7920 4c56 4d32 2076 6572 7369 ed by LVM2 versi00001b70: 6f6e 2032 2e30 322e 3534 2831 2920 2832 on 2.02.54(1) (200001b80: 3030 392d 3130 2d32 3629 3a20 4d6f 6e20 009-10-26): Mon00001b90: 4170 7220 3234 2030 383a 3534 3a32 3220 Apr 24 08:54:2200001ba0: 3230 3137 0a0a 636f 6e74 656e 7473 203d 2017..contents =00001bb0: 2022 5465 7874 2046 6f72 6d61 7420 566f "Text Format Vo00001bc0: 6c75 6d65 2047 726f 7570 220a 7665 7273 lume Group".vers00001bd0: 696f 6e20 3d20 310a 0a64 6573 6372 6970 ion = 1..descrip00001be0: 7469 6f6e 203d 2022 220a 0a63 7265 6174 tion = ""..creat00001bf0: 696f 6e5f 686f 7374 203d 2022 7562 756e ion_host = "ubun00001c00: 7475 2209 2320 4c69 6e75 7820 7562 756e tu".# Linux ubun00001c10: 7475 2032 2e36 2e33 322d 3231 2d67 656e tu 2.6.32-21-gen00001c20: 6572 6963 2023 3332 2d55 6275 6e74 7520 eric #32-Ubuntu00001c30: 534d 5020 4672 6920 4170 7220 3136 2030 SMP Fri Apr 16 000001c40: 383a 3130 3a30 3220 5554 4320 3230 3130 8:10:02 UTC 201000001c50: 2069 3638 360a 6372 6561 7469 6f6e 5f74 i686.creation_t00001c60: 696d 6520 3d20 3134 3933 3032 3430 3632 ime = 149302406200001c70: 0923 204d 6f6e 2041 7072 2032 3420 3038 .# Mon Apr 24 0800001c80: 3a35 343a 3232 2032 3031 370a 0a00 0000 :54:22 2017.....00001c90: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001ca0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001cb0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001cc0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001cd0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001ce0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001cf0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d00: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d10: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d20: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d30: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d40: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d50: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d60: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d70: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d80: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001d90: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001da0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001db0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001dc0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001dd0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001de0: 0000 0000 0000 0000 0000 0000 0000 0000 ................00001df0: 0000 0000 0000 0000 0000 0000 0000 0000 ...................

MBR的引导代码

提取引导代码

因为引导代码也是MBR的一部分，因此，调整提取MBR的命令即可提取之到文件，而后反编译之

dd if=path_to_your_disc bs=1 count=446 > path_to_mbr_code.binobjdump -D -b binary -m i386 -Maddr16,data16 --adjust-vma=0x7c00 path_to_mbr_code.bin# if you like the intel styleobjdump -D -b binary -m i386 -Maddr16,data16,intel --adjust-vma=0x7c00 path_to_mbr_code.bin

看看效果

一睹真实引导代码风采

现在的引导代码并非只是简单的一段实模式下的二进制程序，因此反编译的结果就差强人意了。如果你想一睹真实代码风貌，请看grub-core/boot/i386/pc/boot.S文件内容

/* -*-Asm-*- *//** GRUB -- GRand Unified Bootloader* Copyright (C) 1999,2000,2001,2002,2005,2006,2007,2008,2009 Free Software Foundation, Inc.** GRUB is free software: you can redistribute it and/or modify* it under the terms of the GNU General Public License as published by* the Free Software Foundation, either version 3 of the License, or* (at your option) any later version.** GRUB is distributed in the hope that it will be useful,* but WITHOUT ANY WARRANTY; without even the implied warranty of* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the* GNU General Public License for more details.** You should have received a copy of the GNU General Public License* along with GRUB. If not, see <;.*/#include <grub/symbol.h>#include <grub/machine/boot.h>/** defines for the code go here*/ /* Print message string */#define MSG(x) movw $x, %si; call LOCAL(message)#define ERR(x) movw $x, %si; jmp LOCAL(error_message) .macro floppypart_start:LOCAL(probe_values): .byte 36, 18, 15, 9, 0LOCAL(floppy_probe): pushw %dx/** Perform floppy probe.*/#ifdef __APPLE__ LOCAL(probe_values_minus_one) = LOCAL(probe_values) - 1 movw MACRO_DOLLAR(LOCAL(probe_values_minus_one)), %si#else movw MACRO_DOLLAR(LOCAL(probe_values)) - 1, %si#endifLOCAL(probe_loop): /* reset floppy controller INT 13h AH=0 */ xorw %ax, %ax int MACRO_DOLLAR(0x13) incw %si movb (%si), %cl /* if number of sectors is 0, display error and die */ testb %cl, %cl jnz 1f/** Floppy disk probe failure.*/ MSG(fd_probe_error_string) jmp LOCAL(general_error)/* "Floppy" */fd_probe_error_string: .asciz "Floppy"1: /* perform read */ movw MACRO_DOLLAR(GRUB_BOOT_MACHINE_BUFFER_SEG), %bx movw %bx, %es xorw %bx, %bx movw MACRO_DOLLAR(0x201), %ax movb MACRO_DOLLAR(0), %ch movb MACRO_DOLLAR(0), %dh int MACRO_DOLLAR(0x13) /* if error, jump to "LOCAL(probe_loop)" */ jc LOCAL(probe_loop) /* %cl is already the correct value! */ movb MACRO_DOLLAR(1), %dh movb MACRO_DOLLAR(79), %ch jmp LOCAL(final_init) .endm .macro scratch /* scratch space */mode: .byte 0disk_address_packet:sectors: .long 0heads: .long 0cylinders: .word 0sector_start: .byte 0head_start: .byte 0cylinder_start: .word 0 /* more space... */ .endm .file "boot.S" .text /* Tell GAS to generate 16-bit instructions so that this code works in real mode. */ .code16.globl _start, start;_start:start: /* * _start is loaded at 0x7c00 and is jumped to with CS:IP 0:0x7c00 */ /* * Beginning of the sector is compatible with the FAT/HPFS BIOS * parameter block. */ jmp LOCAL(after_BPB) nop /* do I care about this ??? */#ifdef HYBRID_BOOT nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop nop jmp LOCAL(after_BPB)#else /* * This space is for the BIOS parameter block!!!! Don't change * the first jump, nor start the code anywhere but right after * this area. */ .org GRUB_BOOT_MACHINE_BPB_START .org 4#endif#ifdef HYBRID_BOOT floppy#else scratch#endif .org GRUB_BOOT_MACHINE_BPB_END /* * End of BIOS parameter block. */LOCAL(kernel_address): .word GRUB_BOOT_MACHINE_KERNEL_ADDR#ifndef HYBRID_BOOT .org GRUB_BOOT_MACHINE_KERNEL_SECTORLOCAL(kernel_sector): .long 1LOCAL(kernel_sector_high): .long 0#endif .org GRUB_BOOT_MACHINE_BOOT_DRIVEboot_drive: .byte 0xff /* the disk to load kernel from */ /* 0xff means use the boot drive */LOCAL(after_BPB):/* general setup */ cli /* we're not safe here! */ /* * This is a workaround for buggy BIOSes which don't pass boot * drive correctly. If GRUB is installed into a HDD, check if * DL is masked correctly. If not, assume that the BIOS passed * a bogus value and set DL to 0x80, since this is the only * possible boot drive. If GRUB is installed into a floppy, * this does nothing (only jump). */ .org GRUB_BOOT_MACHINE_DRIVE_CHECKboot_drive_check: jmp 3f /* grub-setup may overwrite this jump */ testb $0x80, %dl jz 2f3: /* Ignore %dl different from 0-0x0f and 0x80-0x8f. */ testb $0x70, %dl jz 1f2:  movb $0x80, %dl1: /* * ljmp to the next instruction because some bogus BIOSes * jump to 07C0:0000 instead of 0000:7C00. */ ljmp $0, $real_startreal_start: /* set up %ds and %ss as offset from 0 */ xorw %ax, %ax movw %ax, %ds movw %ax, %ss /* set up the REAL stack */ movw $GRUB_BOOT_MACHINE_STACK_SEG, %sp sti /* we're safe again */ /* * Check if we have a forced disk reference here */ movb boot_drive, %al cmpb $0xff, %al je 1f movb %al, %dl1: /* save drive reference first thing! */ pushw %dx /* print a notification message on the screen */ MSG(notification_string) /* set %si to the disk address packet */ movw $disk_address_packet, %si /* check if LBA is supported */ movb $0x41, %ah movw $0x55aa, %bx int $0x13 /* * %dl may have been clobbered by INT 13, AH=41H. * This happens, for example, with AST BIOS 1.04. */ popw %dx pushw %dx /* use CHS if fails */ jc LOCAL(chs_mode) cmpw $0xaa55, %bx jne LOCAL(chs_mode) andw $1, %cx jz LOCAL(chs_mode)LOCAL(lba_mode): xorw %ax, %ax movw %ax, 4(%si) incw %ax /* set the mode to non-zero */ movb %al, -1(%si) /* the blocks */ movw %ax, 2(%si) /* the size and the reserved byte */ movw $0x0010, (%si) /* the absolute address */ movl LOCAL(kernel_sector), %ebx movl %ebx, 8(%si) movl LOCAL(kernel_sector_high), %ebx movl %ebx, 12(%si) /* the segment of buffer address */ movw $GRUB_BOOT_MACHINE_BUFFER_SEG, 6(%si)/** BIOS call "INT 0x13 Function 0x42" to read sectors from disk into memory* Call with %ah = 0x42* %dl = drive number* %ds:%si = segment:offset of disk address packet* Return:* %al = 0x0 on success; err code on failure*/ movb $0x42, %ah int $0x13 /* LBA read is not supported, so fallback to CHS. */ jc LOCAL(chs_mode) movw $GRUB_BOOT_MACHINE_BUFFER_SEG, %bx jmp LOCAL(copy_buffer)LOCAL(chs_mode): /* * Determine the hard disk geometry from the BIOS! * We do this first, so that LS-120 IDE floppies work correctly. */ movb $8, %ah int $0x13 jnc LOCAL(final_init) popw %dx /* * The call failed, so maybe use the floppy probe instead. */ testb %dl, %dl jnb LOCAL(floppy_probe) /* Nope, we definitely have a hard disk, and we're screwed. */ ERR(hd_probe_error_string)LOCAL(final_init): /* set the mode to zero */ movzbl %dh, %eax movb %ah, -1(%si) /* save number of heads */ incw %ax movl %eax, 4(%si) movzbw %cl, %dx shlw $2, %dx movb %ch, %al movb %dh, %ah /* save number of cylinders */ incw %ax movw %ax, 8(%si) movzbw %dl, %ax shrb $2, %al /* save number of sectors */ movl %eax, (%si)setup_sectors: /* load logical sector start (top half) */ movl LOCAL(kernel_sector_high), %eax orl %eax, %eax jnz LOCAL(geometry_error) /* load logical sector start (bottom half) */ movl LOCAL(kernel_sector), %eax /* zero %edx */ xorl %edx, %edx /* divide by number of sectors */ divl (%si) /* save sector start */ movb %dl, %cl xorw %dx, %dx /* zero %edx */ divl 4(%si) /* divide by number of heads */ /* do we need too many cylinders? */ cmpw 8(%si), %ax jge LOCAL(geometry_error) /* normalize sector start (1-based) */ incb %cl /* low bits of cylinder start */ movb %al, %ch /* high bits of cylinder start */ xorb %al, %al shrw $2, %ax orb %al, %cl /* save head start */ movb %dl, %al /* restore %dl */ popw %dx /* head start */ movb %al, %dh/** BIOS call "INT 0x13 Function 0x2" to read sectors from disk into memory* Call with %ah = 0x2* %al = number of sectors* %ch = cylinder* %cl = sector (bits 6-7 are high bits of "cylinder")* %dh = head* %dl = drive (0x80 for hard disk, 0x0 for floppy disk)* %es:%bx = segment:offset of buffer* Return:* %al = 0x0 on success; err code on failure*/ movw $GRUB_BOOT_MACHINE_BUFFER_SEG, %bx movw %bx, %es /* load %es segment with disk buffer */ xorw %bx, %bx /* %bx = 0, put it at 0 in the segment */ movw $0x0201, %ax /* function 2 */ int $0x13 jc LOCAL(read_error) movw %es, %bxLOCAL(copy_buffer): /* * We need to save %cx and %si because the startup code in * kernel uses them without initializing them. */ pusha pushw %ds movw $0x100, %cx movw %bx, %ds xorw %si, %si movw $GRUB_BOOT_MACHINE_KERNEL_ADDR, %di movw %si, %es cld rep movsw popw %ds popa /* boot kernel */ jmp *(LOCAL(kernel_address))/* END OF MAIN LOOP *//** BIOS Geometry translation error (past the end of the disk geometry!).*/LOCAL(geometry_error): ERR(geometry_error_string)/** Read error on the disk.*/LOCAL(read_error): movw $read_error_string, %siLOCAL(error_message): call LOCAL(message)LOCAL(general_error): MSG(general_error_string)/* go here when you need to stop the machine hard after an error condition */ /* tell the BIOS a boot failure, which may result in no effect */ int $0x18LOCAL(stop): jmp LOCAL(stop)notification_string: .asciz "GRUB "geometry_error_string: .asciz "Geom"hd_probe_error_string: .asciz "Hard Disk"read_error_string: .asciz "Read"general_error_string: .asciz " Error\r\n"/** message: write the string pointed to by %si** WARNING: trashes %si, %ax, and %bx*/ /* * Use BIOS "int 10H Function 0Eh" to write character in teletype mode * %ah = 0xe %al = character * %bh = page %bl = foreground color (graphics modes) */1: movw $0x0001, %bx movb $0xe, %ah int $0x10 /* display a byte */LOCAL(message): lodsb cmpb $0, %al jne 1b /* if not end of string, jmp to display */ ret /* * Windows NT breaks compatibility by embedding a magic * number here. */#ifdef HYBRID_BOOT .org 0x1b0LOCAL(kernel_sector): .long 1LOCAL(kernel_sector_high): .long 0#endif .org GRUB_BOOT_MACHINE_WINDOWS_NT_MAGICnt_magic: .long 0 .word 0 /* * This is where an MBR would go if on a hard disk. The code * here isn't even referenced unless we're on a floppy. Kinda * sneaky, huh? */ .org GRUB_BOOT_MACHINE_PART_START#ifndef HYBRID_BOOT floppy#else scratch#endif .org GRUB_BOOT_MACHINE_PART_END/* the last 2 bytes in the sector 0 contain the signature */ .word GRUB_BOOT_MACHINE_SIGNATURE

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