Bless image without using virtual machine.

[dsaul]

Hey There,

I wanted to ask if there was a way to "bless" a disk image without booting up an emulator and double clicking the system folder?

To see what makes an imaged blessed I created a new image with the following:

cp2 create-disk-image built.dsk 500M hfs

Copied a minimal 7.1 install to this image using:

cp2 copy base-7.1-r2024-07-11.dsk * built.dsk

Attempted to boot from this image, which didn't work (expected).

After booting up from a working 7.1 image, I blessed the newly created image by double clicking on the system suitcase and immediately shutting down.

Opening these two files in a hex editor, we can see that the start of the image is slightly different:

I'm not familiar with HFS enough to know how to go from here. I could just copy this bit over whenever I needed to bless, but that doesn't seem right.

Does anyone have any thoughts?

[fadden]

Blocks 0 and 1 hold the boot blocks on an HFS volume. The format is described here. I didn't try to set this up in the volume formatter because I wasn't sure if a "one size fits all" boot block would work generally, since it has executable 68K code in it. There's a flag in the version field that seems to disable execution of code in the boot block, so maybe the code is only needed for specific hardware or older machines? Might be worth playing with to see if there's a general solution that will save a step when creating new system volumes.

FWIW, you can save a copy of the boot blocks like this:

$ cp2 read-block bootable-image.dsk 0 > boot-block0.txt
$ cp2 read-block bootable-image.dsk 1 > boot-block1.txt

and then write them to new image disk images with this:

$ cp2 write-block built.dsk 0 boot-block0.txt
$ cp2 write-block built.dsk 1 boot-block1.txt

Additional disks can be written from the two text files. You could also just copy the blocks directly:

$ cp2 copy-blocks bootable-image.dsk built.dsk 0 0 2
Copying blocks 0-1 to 0-1
Copied 2 blocks, encountered 0 errors

(One caution: if you're working with an APM multi-part volume image then you need to specify the HFS volume, or you'll end up overwriting the partition map.)

FWIW, here's what I found in an old Mac Classic.

000000: 4c 4b 60 00 00 86 00 17 00 00 06 53 79 73 74 65  LK`··Ü·····Syste
000010: 6d 20 20 20 20 20 20 20 20 20 06 46 69 6e 64 65  m         ·Finde
000020: 72 20 20 20 20 20 20 20 20 20 07 4d 61 63 73 62  r         ·Macsb
000030: 75 67 20 20 20 20 20 20 20 20 0c 44 69 73 61 73  ug        ·Disas
000040: 73 65 6d 62 6c 65 72 20 20 20 0d 53 74 61 72 74  sembler   ·Start
000050: 55 70 53 63 72 65 65 6e 20 20 06 46 69 6e 64 65  UpScreen  ·Finde
000060: 72 20 20 20 20 20 20 20 20 20 0e 43 6c 69 70 62  r         ·Clipb
000070: 6f 61 72 64 20 46 69 6c 65 20 00 0a 00 14 00 00  oard File ······
000080: 43 00 00 00 80 00 00 02 00 00 22 38 01 08 48 41  C···Ä·····"8··HA
000090: 0c 41 00 04 6e 2c 72 00 50 f9 00 01 ff f0 42 b9  ·A··n,r·P˘··ˇBπ
0000a0: 00 03 ff f0 4a b9 00 01 ff f0 67 16 70 02 48 40  ··ˇJπ··ˇg·p·H@
0000b0: d1 b8 01 08 d1 b8 08 24 d1 b8 02 66 d1 b8 01 0c  —∏··—∏·$—∏·f—∏··
0000c0: 72 04 20 78 02 a6 0c 41 00 08 6f 02 72 08 d1 fb  r· x·¶·A··o·r·—˚
0000d0: 10 ae 2f 08 70 07 41 f8 0a b8 42 98 51 c8 ff fc  ·Æ/·p·A¯·∏BòQ»ˇ¸
0000e0: 34 3a ff 9a 70 16 c0 c2 22 00 a7 1e 43 f8 01 54  4:ˇöp·¿¬"·ß·C¯·T
0000f0: 53 42 32 82 42 a1 42 a1 42 61 23 08 46 58 55 41  SB2ÇB°B°Ba#·FXUA
000100: 66 fa 33 3c ff ef 42 78 01 84 72 fc 70 0f 14 38  f˙3<ˇÔBx·Ñr¸p··8
000110: 02 06 c0 02 d0 40 48 40 10 02 e4 48 c0 41 48 40  ··¿·–@H@··‰H¿AH@
000120: 21 c0 01 8e 70 0f 14 38 02 09 c0 02 e5 48 21 c0  !¿·ép··8··¿·ÂH!¿
000130: 02 f4 10 02 e4 48 c0 41 21 c0 02 f0 41 f8 03 40  ·Ù··‰H¿A!¿·A¯·@
000140: 72 50 42 58 51 c9 ff fc 70 1e c0 fa ff 2e 32 38  rPBXQ…ˇ¸p·¿˙ˇ.28
000150: 01 08 e2 49 c0 c1 54 40 32 00 a7 1e 21 c8 03 4e  ··‚I¿¡T@2·ß·!»·N
000160: 30 c1 31 fc 00 02 03 4c 9e fc 00 32 20 4f 31 78  0¡1¸···Lû¸·2 O1x
000170: 02 10 00 16 a0 0f 66 00 01 b2 de fc 00 32 43 f8  ····†·f··≤fi¸·2C¯
000180: 0a d8 41 fa fe 86 70 10 a0 2e 55 4f 2f 0f 48 78  ·ÿA˙˛Üp·†.UO/·Hx
000190: 09 fa 20 78 08 10 4e 90 30 1f e6 48 31 c0 01 06  ·˙ x··Nê0·ÊH1¿··
0001a0: 08 38 00 06 02 0b 56 f8 08 d3 a8 52 43 fa fe 9c  ·8····V¯·”®RC˙˛ú
0001b0: 76 01 61 00 01 98 0c 44 40 00 6e 02 70 ff 3f 00  v·a··ò·D@·n·pˇ?·
0001c0: 66 04 61 00 01 f0 a8 53 55 4f 42 b8 0a f2 a9 95  f·a··®SUOB∏·Ú©ï
0001d0: 4a 5f 6b 00 01 56 3e 1f 20 5f a0 57 21 f8 02 a6  J_k··V>· _†W!¯·¶
0001e0: 01 18 59 4f 2f 3c 44 53 41 54 42 67 a9 a0 2a 1f  ··YO/<DSATBg©†*·
0001f0: 67 00 01 1e 20 45 21 d0 02 ba a8 fe 70 28 61 00  g··· E!–·∫®˛p(a·

000000: 01 16 20 3c 00 00 06 00 32 3a fd fe 67 0a 6a 04  ·· <····2:˝˛g·j·
000010: 70 01 e2 58 91 b8 01 0c 04 b8 00 00 04 00 01 0c  p·‚Xë∏···∏······
000020: 43 fa fe 08 61 00 01 24 66 00 00 f4 4e 91 70 f6  C˙˛·a··$f··ÙNëpˆ
000030: 61 00 00 e4 43 fa fe 04 61 00 01 10 66 08 4e 91  a··‰C˙˛·a···f·Në
000040: 70 f5 61 00 00 d2 43 f8 0a d8 76 ff 61 00 00 fe  pıa··“C¯·ÿvˇa··˛
000050: 66 00 00 04 4e 91 21 f8 02 a6 02 b2 70 0c a7 22  f···Në!¯·¶·≤p·ß"
000060: 21 c8 0a ec a0 2c a0 4f 2f 05 a9 a3 7c 00 59 4f  !»·Ï†,†O/·©£|·YO
000070: 2f 3c 49 4e 49 54 3f 06 a9 a0 2e 17 67 00 00 64  /<INIT?·©†.·g··d
000080: a9 92 20 47 20 50 4e 90 20 47 20 50 30 3c 4e 71  ©í G PNê G P0<Nq
000090: 30 c0 30 c0 52 46 0c 46 00 20 6d d2 70 02 48 40  0¿0¿RF·F· m“p·H@
0000a0: a4 4c 43 f8 09 70 21 c9 09 6c 41 fa fd be 70 10  §LC¯·p!…·lA˙˝æp·
0000b0: a0 2e 41 fa fd 66 43 f8 02 e0 70 10 a0 2e 42 78  †.A˙˝fC¯·‡p·†.Bx
0000c0: 09 00 47 fa fd 96 61 6a 67 08 47 fa fd 4e 61 62  ··G˙˝ñajg·G˙˝Nab
0000d0: 66 0a 42 67 42 a7 2f 0b 20 4f a9 f2 70 29 a9 c9  f·BgBß/· O©Úp)©…
0000e0: a9 ff 58 4f 60 ae 61 08 20 79 00 40 00 04 4e d0  ©ˇXO`Æa· y·@··N–
0000f0: 9e fc 00 32 20 4f 31 7c ff fb 00 18 31 7c 00 07  û¸·2 O1|ˇ˚··1|··
000100: 00 1a 31 78 02 10 00 16 a0 04 de fc 00 32 4e 75  ··1x····†·fi¸·2Nu
000110: 7e 00 60 00 fe e6 4a 47 67 02 a9 c9 4e 75 06 b8  ~·`·˛ÊJGg·©…Nu·∏
000120: 00 00 04 00 01 0c 60 00 ff 1e 61 c4 70 64 a9 c9  ······`·ˇ·aƒpd©…
000130: 60 b4 70 13 42 a7 51 c8 ff fc 2f 4b 00 12 20 4f  `¥p·BßQ»ˇ¸/K·· O
000140: a0 0c de fc 00 50 4a 40 4e 75 76 00 9e fc 00 32  †·fi¸·PJ@Nuv·û¸·2
000150: 20 4f 74 ff 45 e8 00 12 24 c9 42 9a 42 1a 14 fc   OtˇEË··$…BöB··¸
000160: 00 01 24 bc 00 01 10 00 a0 00 66 2c a0 11 66 26  ··$º····†·f,†·f&
000170: 28 1a 7c 02 e1 46 98 86 4a 43 6b 2e 66 22 22 78  (·|··FòÜJCk.f""x
000180: 01 0c 93 c4 24 c9 24 c4 58 4a 34 fc 00 01 24 86  ··ìƒ$…$ƒXJ4¸··$Ü
000190: a0 02 66 02 74 00 a0 01 30 02 de fc 00 32 4e 75  †·f·t·†·0·fi¸·2Nu
0001a0: 32 7c 60 00 d8 86 7c 00 60 da 20 04 a1 1e 22 48  2|`·ÿÜ|·`⁄ ·°·"H
0001b0: 20 4f 60 d0 2f 3c 01 56 02 00 42 a7 2f 3c 60 00   O`–/<·V··Bß/<`·
0001c0: 00 40 42 67 4b f9 00 00 fd 90 45 ed 00 72 2f 0f  ·@BgK˘··˝êEÌ·r/·
0001d0: 48 52 48 6f 00 0e 48 6a 00 06 42 67 42 a7 a8 ec  HRHo··Hj··BgBß®Ï
0001e0: de fc 00 0e 4e 75 da da da da da da da da da da  fi¸··Nu⁄⁄⁄⁄⁄⁄⁄⁄⁄⁄
0001f0: da da da da da da da da da da da da da da da da  ⁄⁄⁄⁄⁄⁄⁄⁄⁄⁄⁄⁄⁄⁄⁄⁄

[dsaul]

That's awesome, I didn't know that doc existed.

I'm sure the copy functions you provided will do well enough, reading the struct layout from that page, unless I get more fancy with what I'm doing it should be good.

In my search, I found this page: https://ss64.com/mac/bless.html Which then led me to this file in apple's bless command: https://github.com/apple-opensource/bless/blob/master/files/bootblockdata which is a carbon copy of what I found. I believe that they just copied this raw data (in earlier versions, the file doesn't seem to be used now). This gives me confidence that this'll work.

Thanks Andy!

[fadden]

Very interesting. It looks like bootblockdata is supposed to be installed in /usr/share/misc, and supplied as a command-line argument with --bootBlockFile. It looks like the contents are also embedded in cdbootdata and hdbootdata (at +$7040).

The bless command does a ton of other things, but since you were able to boot system 7 with only the boot block change, I think it's safe to ignore that for vintage systems.

I opened an issue: #42