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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

...e two nibbles */ + call write_hex_value + +partition_table_scan: + movw $partition_table, %si + movw $0x04, %cx /* number of table entries */ + +partition_entry_next: + testb $flag_active, (%si) /* is active (bootable) flag set? */ + jnz msg_partition_active + + addw $16, %si /* next entry */ + loopw partition_entry_next + + jmp print_boot_message /* no active parition, so don't try to read a sector */ + +msg_partition_active: + movb $0x05, %ch /* convert CL countdown to partition number */ + subb %cl, %ch /* CL:partition translations 4:1, 3:2, 2:3, 1:4 */ + movb %ch, %dl /* value to...

...y or lazyness. As the code doesn't do any harm (supposedly) in that case the coder just lets it run. > > - I assume that > movw $0x7c00, %bx > movw $4, %cx /* Sector count */ > movl (lba_offset), %eax > 2: > call read_sector > ... > loopw 2b > shall load the bytes of isolinux.bin to address 0x7c00. Yes, I think so. It loads the next bootloader (which is four secors instead of the usual one) to 0x7c00. It's most likely is isolinux as it has confirmed the signature (the part that fails for David which started this thread), r...

...e two nibbles */ + call write_hex_value + +partition_table_scan: + movw $partition_table, %si + movw $0x04, %cx /* number of table entries */ + +partition_entry_next: + testb $flag_active, (%si) /* is active (bootable) flag set? */ + jnz msg_partition_active + + addw $16, %si /* next entry */ + loopw partition_entry_next + + jmp print_boot_message /* no active parition */ + +msg_partition_active: + movb $0x05, %ch /* convert CL countdown to partition number */ + subb %cl, %ch /* CL:partition translations 4:1, 3:2, 2:3, 1:4 */ + movb %ch, %dl /* value to write is partition number [1-4] */...

...e two nibbles */ + call write_hex_value + +partition_table_scan: + movw $partition_table, %si + movw $0x04, %cx /* number of table entries */ + +partition_entry_next: + testb $flag_active, (%si) /* is active (bootable) flag set? */ + jnz msg_partition_active + + addw $16, %si /* next entry */ + loopw partition_entry_next + + jmp print_boot_message /* no active parition, so don't try to read a sector */ + +msg_partition_active: + movb $0x05, %ch /* convert CL countdown to partition number */ + subb %cl, %ch /* CL:partition translations 4:1, 3:2, 2:3, 1:4 */ + movb %ch, %dl /* value to...

This patches add support for dynamic sectors to GPT MBR code. First 3 patches are trick and optimizations to gain some space for the forth patch. I have a modified version of SeaBIOS, some code and some script o test it I'll send on a different mail.

..." scn_pnp: call crlf /* $PnP Scan */ movw $0xf000, %dx pushw %dx popw %es movw $0, %si movw $0x1000, %cx /* 0x506E5024 */ movw $0x5024, %dx movw $0x506E, %bx ch_pnp: es lodsw cmpw %dx, %ax jne ch_pnp_l es lodsw cmpw %bx, %ax je pr_pnp ch_pnp_l: addw $14, %si andw $0xFFF0, %si loopw ch_pnp jmp end pr_pnp: pushw %si call wrstr .ascii "$PnP-\0" movw %es, %dx call wrhexw movb $':, %al call wrchr popw %dx andw $0xFFF0, %dx call wrhexw #endif /* DEBUG_PNP */ call crlf end: jmp bootfail ASCII_MARKER1 "wc" wrchr: movb $0x0e, %ah movb (BIOS_p...

...-24: Low word */ /* * Load sectors. We do this one at a time mostly to avoid * pitfalls and to share code with the stock MBR code. */ movw $0x7c00, %bx movw $4, %cx /* Sector count */ movl (lba_offset), %eax 2: call read_sector jc disk_error incl %eax addb $(512 >> 8), %bh loopw 2b /* Dump out the bytes of the first sector. */ pusha mov $0x7c00, %di mov $16, %dx 2: mov $16, %cx 1: mov (%di), %al inc %di call print_al loop 1b call print_string .ascii "\r\n" dec %dx jnz 2b call print_string .ascii "Key?\r\n" xor %ax, %ax int $0x16...

This set of patches add some support for sector size >512. Currently it fixes extlinux, MBR for GPT and ext partitions. Other code is unaffected. This set of patches has been tested on a read Dell machine running a beta firmware.