Hi,
John Paul Adrian Glaubitz wrote:
> I have read the genisoimage manpage and I have to admit, I haven't fully
> understood
> yet how it is supposed to work. It seems we have to specify the bootloader
> code
> with -G, thus -G cdboot.img. But -B is apparently used to pass a whole
> directory
> name which means I don't understand how genisoimage knows which is the second
> stage bootloader.
Dumping here what i learned when Vladimir Serbinko told me how to
do it with xorriso underneath grub-mkrescue:
libisofs/doc/boot_sectors.txt has:
=========================================================================
GRUB2 SUN SPARC Core File Address
Sources:
Mail conversations with Vladimir Serbinenko.
GRUB2 lets libisofs write after the disk label block the address and size of a
data file in the ISO image. E.g. of /boot/grub/sparc64-ieee1275/core.img.
This is combined with a SUN Disk Label which exposes only the single partition
describing the overall ISO filesystem size.
Byte Range | Value | Meaning
------------ | ---------- | --------------------------------------------------
512 - 551 | opaque | Code and data provided by GRUB2
| |
552 - 559 | offset | Start byte number of the file. 64-bit big-endian.
| |
560 - 563 | size | Number of bytes in the file. 32-bit big-endian.
| |
564 - 32767 | opaque | Code and data provided by GRUB2
| |
------------ | ---------- | --------------------------------------------------
=========================================================================
(There is a section "SUN Disk Label and boot images for SUN SPARC" before
that special GRUB description.)
man xorrisofs:
=========================================================================
-B disk_path[,disk_path ...]
Cause one or more data files on disk to be written after the end
of the ISO image. A SUN Disk Label will be written into the
first 512 bytes of the ISO image which lists this image as
partition 1 and the given disk_paths as partition 2 up to 8.
The disk files should contain suitable boot images for SUN SPARC
systems.
The pseudo disk_path "..." causes that all empty partition
entries become copies of the last non-empty entry. If no other
disk_path is given before "..." then all partitions describe the
ISO image. In this case, the boot loader code has to be imported
by option -G.
=========================================================================
util/grub-mkrescue.c does
=========================================================================
if (source_dirs[GRUB_INSTALL_PLATFORM_SPARC64_IEEE1275]
&& system_area == SYS_AREA_SPARC)
{
...
xorriso_push ("-G");
xorriso_push (sysarea_img);
xorriso_push ("-B");
xorriso_push (",");
xorriso_push ("--grub2-sparc-core");
xorriso_push ("/boot/grub/sparc64-ieee1275/core.img");
=========================================================================
The mkisofs emulation option --grub2-sparc-core does the stuff described
in boot_sectors.txt.
(And i see nice examples of grub_util_fopen() and fwrite(3) by which
grub-mkrescue could zero the EFI partition's partition table after
mformat did its work ...)
I hope this helps to get more insight. More background might be known
to Vladimir.
Have a nice day :)
Thomas
