Hi, > Again, this is an FDD 2880K image and there is no MBR there. Your > interpretation is wrong.
In respect to MBR partition table, mformat source has at https://sources.debian.org/src/mtools/4.0.23-1/mformat.c/#L1375 code with this comment: /* install fake partition table pointing to itself */ > What kind of image is used on MS ISO Win image? FDD or HDD one? Probably FDD (however this might be exactly defined). There is a 0xaa 0x55 signature, piossibly x86 boot code, and clearly no partition table. Chris Murphy exposed on https://drive.google.com/open?id=1JgPv8EBHDn5A7hTEwewGK1MuFHvHbJnr as block 0 of the Microsoft El Torito boot image for EFI: 00103800 eb 3c 90 4d 53 44 4f 53 35 2e 30 00 02 01 01 00 |.<.MSDOS5.0.....| 00103810 02 e0 00 40 0b f0 09 00 12 00 02 00 00 00 00 00 |...@............| 00103820 00 00 00 00 00 00 29 c0 56 ef 00 45 46 49 53 45 |......).V..EFISE| 00103830 43 54 4f 52 20 20 46 41 54 31 32 20 20 20 fa 33 |CTOR FAT12 .3| 00103840 c0 8e d0 bc 00 7c 16 07 bb 78 00 36 c5 37 1e 56 |.....|...x.6.7.V| 00103850 16 53 bf 3e 7c b9 0b 00 fc f3 a4 06 1f c6 45 fe |.S.>|.........E.| 00103860 0f 8b 0e 18 7c 88 4d f9 89 47 02 c7 07 3e 7c fb |....|.M..G...>|.| 00103870 cd 13 72 79 33 c0 39 06 13 7c 74 08 8b 0e 13 7c |..ry3.9..|t....|| 00103880 89 0e 20 7c a0 10 7c f7 26 16 7c 03 06 1c 7c 13 |.. |..|.&.|...|.| 00103890 16 1e 7c 03 06 0e 7c 83 d2 00 a3 50 7c 89 16 52 |..|...|....P|..R| 001038a0 7c a3 49 7c 89 16 4b 7c b8 20 00 f7 26 11 7c 8b ||.I|..K|. ..&.|.| 001038b0 1e 0b 7c 03 c3 48 f7 f3 01 06 49 7c 83 16 4b 7c |..|..H....I|..K|| 001038c0 00 bb 00 05 8b 16 52 7c a1 50 7c e8 92 00 72 1d |......R|.P|...r.| 001038d0 b0 01 e8 ac 00 72 16 8b fb b9 0b 00 be e6 7d f3 |.....r........}.| 001038e0 a6 75 0a 8d 7f 20 b9 0b 00 f3 a6 74 18 be 9e 7d |.u... .....t...}| 001038f0 e8 5f 00 33 c0 cd 16 5e 1f 8f 04 8f 44 02 cd 19 |._.3...^....D...| 00103900 58 58 58 eb e8 8b 47 1a 48 48 8a 1e 0d 7c 32 ff |XXX...G.HH...|2.| 00103910 f7 e3 03 06 49 7c 13 16 4b 7c bb 00 07 b9 03 00 |....I|..K|......| 00103920 50 52 51 e8 3a 00 72 d8 b0 01 e8 54 00 59 5a 58 |PRQ.:.r....T.YZX| 00103930 72 bb 05 01 00 83 d2 00 03 1e 0b 7c e2 e2 8a 2e |r..........|....| 00103940 15 7c 8a 16 24 7c 8b 1e 49 7c a1 4b 7c ea 00 00 |.|..$|..I|.K|...| 00103950 70 00 ac 0a c0 74 29 b4 0e bb 07 00 cd 10 eb f2 |p....t).........| 00103960 3b 16 18 7c 73 19 f7 36 18 7c fe c2 88 16 4f 7c |;..|s..6.|....O|| 00103970 33 d2 f7 36 1a 7c 88 16 25 7c a3 4d 7c f8 c3 f9 |3..6.|..%|.M|...| 00103980 c3 b4 02 8b 16 4d 7c b1 06 d2 e6 0a 36 4f 7c 8b |.....M|.....6O|.| 00103990 ca 86 e9 8a 16 24 7c 8a 36 25 7c cd 13 c3 0d 0a |.....$|.6%|.....| 001039a0 4e 6f 6e 2d 53 79 73 74 65 6d 20 64 69 73 6b 20 |Non-System disk | 001039b0 6f 72 20 64 69 73 6b 20 65 72 72 6f 72 0d 0a 52 |or disk error..R| 001039c0 65 70 6c 61 63 65 20 61 6e 64 20 70 72 65 73 73 |eplace and press| 001039d0 20 61 6e 79 20 6b 65 79 20 77 68 65 6e 20 72 65 | any key when re| 001039e0 61 64 79 0d 0a 00 49 4f 20 20 20 20 20 20 53 59 |ady...IO SY| 001039f0 53 4d 53 44 4f 53 20 20 20 53 59 53 00 00 55 aa |SMSDOS SYS..U.| > If FDD then you cannot interpret boot sector as MBR. This is wrong. It's others who interpret it and at least one takes the "fake" partition table entry by mformat for a reason to early stall its boot process. I just have to explain users of grub-mkrescue ISOs why they don't work. The plight of the programmer whose software was the last to touch it. > > The only thing that was found to not work is a MBR partition entry 1 which > > starts at LBA 0. Probably it needs to have non-zero block count and non-zero > > type. > Again, on what type of image? FDD or HDD? Made by the mformat run of grub-mkrescue. Vladimir can probably tell you more about what kind of image he expects. > First of all look at mformat code I did before starting this thread. The bytes in question are intended as "fake" partition table. > If mkfs.fat images work on Macbooks then I would leave mformat as > default and add an option to switch between mformat and mkfs.fat. Why that ? Either mformat's result is ok or it is not. Offering an alternative could start a new branch of cargo cult. Explaining the differences will quickly raise the question why staying with the unusual block0 bytes from mformat at all. I understand that GRUB wants to use a GNU program, and i am careful not to spoil anything that works. Thus my proposal as it is. I will not be overly sad if the proposal is rejected. After all it is quite easy to override the ideas of grub-mkrescue before the ISO gets packed up. In practice, it's preference for GPT makes more problems than its preference for mformat. Have a nice day :) Thomas _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel
