search for: partition_support

Thomas Schmitt wrote: > I have some problems understanding the details of the program's flow. > > - The code inside PARTITION_SUPPORT is supposed to be inactive with > MBR isohdpfx.bin. It belongs to isohybrid --partok which is equivalent > to MBRs isohdppx*.bin. Debian uses isohdpfx.bin. Yes. isohdpfx.bin is generated from isohdpfx.S in which PARTITION_SUPPORT is not defined. isohdppx.bin us generated from isohdppx....

Hi, > The ISO will boot successfully (when chainloaded from grub) on 2 and > 3, but not on 5 and 6. Did you try with a boot loader other than GRUB ? Afaik, the MBRs of newly bought USB sticks often contain code which hops on the MBR code of the partition that is marked by the boot flag. At least one could exclude that your problem is in a GRUB peculiarity. Have a nice day :) Thomas

...have bystanders who can read x86 assembler code or know easy-to-grasp > reference docs? > (I left machine code programming when i gave up using my VIC-20.) > > The MBR template isohdppx.bin stems from > http://git.zytor.com/syslinux/syslinux.git/tree/mbr/isohdpfx.S > with macro PARTITION_SUPPORT defined. > > One can see the error message text in there: > > bad_signature: > call error > .ascii "isolinux.bin missing or corrupt.\r\n" > > It seems to be reached only if the seen isolinux.bin does not bear the > magic number of isohybrid c...

Hi, do we have bystanders who can read x86 assembler code or know easy-to-grasp reference docs? (I left machine code programming when i gave up using my VIC-20.) The MBR template isohdppx.bin stems from http://git.zytor.com/syslinux/syslinux.git/tree/mbr/isohdpfx.S with macro PARTITION_SUPPORT defined. One can see the error message text in there: bad_signature: call error .ascii "isolinux.bin missing or corrupt.\r\n" It seems to be reached only if the seen isolinux.bin does not bear the magic number of isohybrid capable isolinux.bin. cmpl $HYBRID_MAGIC,(isolinux_h...

...ion to which you copy the image encloses the ISO, exposes it for mounting, and protects it from partition editors. (Another idea from assembler riddling turned out to be a red herring.) Without understanding the language or the BIOS habits of MBR booting, i assume that the code inside the #ifdef PARTITION_SUPPORT condition shall get the start block address of the partition from where the MBR was loaded. At offset 8 of an MBR partition slot is stored the 4 byte LBA of the partition start. /* We have non-GPT partition information */ 2: movl 8(%si), %ecx This theory is supported by the numbers in the GPT...

Thomas Schmitt wrote: > I ponder whether it would be possible to create a diagnostic MBR > which does not necessarily have to boot but rather tells what the > isohybrid MBR would perceive: Presence of partition table, > EBIOS or CBIOS, block address used with INT 13, content of the block > read by the first INT 13, ... ... > The diagnostic MBR should only use 432 bytes because at

...o adding the GPT entry length between the MBR and GPT entries. That's four more bytes. So 16+4=20. I think si points at the fake MBR entry at the insruction you ask about. But isohdpfx.S is buggy: /* Check to see if we have a partition table entry */ xorl %ebx, %ebx xorl %ecx, %ecx #ifdef PARTITION_SUPPORT andw %si, %si /* %si == 0 -> no partition data */ jz 1f testb $0x7f, (%si) /* Invalid active flag field? */ jnz 1f cmpb %cl, 4(%si) /* Partition type zero == invalid? */ je 1f cmpl $0x58504721, %eax /* !GPT signature in EAX? */ jne 2f cmpb $0xed, 4(%si) /* EFI partition type? */ jn...

...on ".bootsec", "a", @nobits .globl bootsec bootsec: .space 512 .text .globl _start _start: .byte 0x33, 0xed /* xorw %bp, %bp */ cli movw %bp, %ss movw $stack, %sp sti cld /* Check to see if we have a partition table entry */ xorl %ebx, %ebx xorl %ecx, %ecx #ifdef PARTITION_SUPPORT andw %si, %si /* %si == 0 -> no partition data */ jz 1f testb $0x7f, (%si) /* Invalid active flag field? */ jnz 1f cmpb %cl, 4(%si) /* Partition type zero == invalid? */ je 1f cmpl $0x58504721, %eax /* !GPT signature in EAX? */ jne 2f cmpb $0xed, 4(%si) /* EFI partition type? */ jn...