GRUB on Open Firmware (PowerPC)

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This article covers installation of the GRUB bootloader on PowerPC machines with Open Firmware. This corresponds to GRUB_PLATFORMS=ieee1275 for ppc and ppc64 architectures, and to the --target=powerpc-ieee1275 option of grub-install. IEEE standard 1275 was the official standard for Open Firmware, sometimes abbreviated as OFW or OF.

Note
Linux PowerPC profiles (default/linux/powerpc/*) set USE flag grub_platforms_ieee1275 by default for sys-boot/grub, so no special setting of GRUB_PLATFORMS is needed in /etc/portage/make.conf.

Installing the bootloader

Apple NewWorld Macs (PowerPC)

NewWorld Macs are Macs with Open Firmware version 3 (OF3) or later (OF3+). NewWorld Macs will show a graphical boot selection when holding the ⌥/Option/Alt key right after the chime, until a startup selection is shown on the screen. This will only work well when a CHRP script that includes an os-badge is blessed (attribute :tbxi) on a HFS volume.

Important
The precondition for this example is that /boot is a separate ext2 partition. Other filesystems are possible when the list of GRUB modules is adapted accordingly. If /boot is on the root partition, the example has to be adapted accordingly as well.
  • NewWorld Apple Mac computer (1999—2006).
  • /boot is a separate ext2 partition.
  • Apple Partition Map (APM) consisting of:
    • NewWorld Bootblock as Apple_Boot
    • Filesystem HFS.
    • As any partition number (at the beginning of the disk is preferred, but not required).
  • Apple specific os-badge.

NewWorld Bootblock partition

Note
The use of sys-fs/mac-fdisk is highly recommended. Even though package sys-block/parted can also create Apple Partition Map (APM) style partitions it is not as verbose about partition types.

First, a NewWorld Bootblock has to be created using mac-fdisk:

root #emerge --ask sys-fs/mac-fdisk
root #mac-fdisk /dev/sda

At the interactive command prompt this partition can either be created manually e.g. by using the C command for "create new partition, specifying the partition type", or semi-automatic by using the b command for "create new 800k Apple_Bootstrap partition (used by yaboot)". Either way you should get a bootable HFS partition of either the type Apple_Boot or Apple_Bootstrap. The partition name is optional but helps when listing the partitions. All values are entered by hand without automatism of any kind.

The following example uses the free space (type Apple_Free) right after the partition table. If this wasn't taken care of e.g. when installing Mac OS X, per default only 128 MB will be free here, which should barely be enough for this purpose. Older versions of Mac OS X don't add free space between partitions, so the NewWorld Bootblock will have to be added behind the already existing partitions.

Normally 800 KB is used but any size big enough for a HFS filesystem and the GRUB core files will do. In this example, the hole between the partition table and the first partition (Mac OS X Tiger) is 1.1 GB. It starts at block 64 (base column) and is 2359232 blocks long (length column). Since this is enough to add 128 MB "holes" before and after, the partition will add two more Apple_Free holes. The block numbers to enter have to be calculated first: 128 MB Apple_Free "holes" are 262144 blocks in size, so the first block will have to be 64 (base) + 262144 (Apple_Free) = 262208. Since the original Apple_Free "hole" in this specific example (/dev/sda2) has 2359232 blocks, another hole is left at the end if the size of the bootstrap partition is 2359232 - (2 * 262144) = 1834944.

To get this done, the key sequence p (print partition table), C (create partition with type also specified; type uppercase C!), 262208 (first block), 1834944 (length), "NewWorld Bootblock" (name of partition; use quotes!) and Apple_Boot (type of partition). To check if this worked, use p again to list the new partition table. Note that two more partitions were added and the numbers behind those partitions have been shifted accordingly ("Linux Boot" was /dev/sda9 and got shifted to /dev/sda11). All modifications are done in memory and will be saved with w (write the partition table), followed by y (to confirm). To restart if something got messed up simply quit without writing the modifications. Type q for quit.

Important
For strings use quotation marks " if they contain whitespace(s)! Since partition types use underlines _ only, this is mainly important for (optional) partition names. However, for a better understanding of what is what it is recommended to use partition names. Partition names can also be used for referring to partitions using the PARTLABEL= directive, e.g. in /etc/fstab.
root #mac-fdisk /dev/sda 
/dev/sda
Command (? for help): p
        #                    type name                  length   base      ( size )  system
/dev/sda1     Apple_partition_map Apple                     63 @ 1         ( 31.5k)  Partition map
/dev/sda2              Apple_Free Extra                2359232 @ 64        (  1.1G)  Free space
/dev/sda3               Apple_HFS Tiger              209715200 @ 2359296   (100.0G)  HFS
/dev/sda4              Apple_Free Extra                 262144 @ 212074496 (128.0M)  Free space
/dev/sda5               Apple_HFS Leopard            314572800 @ 212336640 (150.0G)  HFS
/dev/sda6              Apple_Free Extra                 262144 @ 526909440 (128.0M)  Free space
/dev/sda7              Apple_Boot Apple Hardware Test    100898 @ 527171584 ( 49.3M)  Unknown
/dev/sda8              Apple_Free Extra                 262144 @ 527272482 (128.0M)  Free space
/dev/sda9         Apple_UNIX_SVR2 Linux Boot           2097152 @ 527534626 (  1.0G)  Linux native
/dev/sda10             Apple_Free Extra                 262144 @ 529631778 (128.0M)  Free space
/dev/sda11        Apple_UNIX_SVR2 Gentoo Linux       134217728 @ 529893922 ( 64.0G)  Linux native
/dev/sda12             Apple_Free Extra                 262144 @ 664111650 (128.0M)  Free space
/dev/sda13        Apple_UNIX_SVR2 Debian Linux       134217728 @ 664373794 ( 64.0G)  Linux native
/dev/sda14             Apple_Free Extra                 262144 @ 798591522 (128.0M)  Free space
/dev/sda15        Apple_UNIX_SVR2 Linux Local         71216270 @ 798853666 ( 34.0G)  Linux native
/dev/sda16             Apple_Free Extra                 262144 @ 870069936 (128.0M)  Free space
/dev/sda17        Apple_UNIX_SVR2 Linux swap          67108864 @ 870332080 ( 32.0G)  Linux native
/dev/sda18             Apple_Free Extra                 262144 @ 937440944 (128.0M)  Free space

Block size=512, Number of Blocks=937703088
DeviceType=0x0, DeviceId=0x0

Command (? for help): C
First block: 262208
Length (in blocks, kB (k), MB (M) or GB (G)): 1834944
Name of partition: "NewWorld Bootblock"
Type of partition: Apple_Boot
Command (? for help): w
IMPORTANT: You are about to write a changed partition map to disk. 
For any partition you changed the start or size of, writing out 
the map causes all data on that partition to be LOST FOREVER. 
Make sure you have a backup of any data on such partitions you 
want to keep before answering 'yes' to the question below! 

Write partition map? [n/y]: y
The partition map has been saved successfully!

Syncing disks.

Partition map written to disk. If any partitions on this disk 
were still in use by the system (see messages above), you will need 
to reboot in order to utilize the new partition map.

Command (? for help): q

The final partition layout of this example looks like this, using mac-fdisk and parted:

root #mac-fdisk -l /dev/sda 
/dev/sda
        #                    type name                  length   base      ( size )  system
/dev/sda1     Apple_partition_map Apple                     63 @ 1         ( 31.5k)  Partition map
/dev/sda2              Apple_Free Extra                 262144 @ 64        (128.0M)  Free space
/dev/sda3              Apple_Boot NewWorld Bootblock   1834944 @ 262208    (896.0M)  Unknown
/dev/sda4              Apple_Free Extra                 262144 @ 2097152   (128.0M)  Free space
/dev/sda5               Apple_HFS Tiger              209715200 @ 2359296   (100.0G)  HFS
/dev/sda6              Apple_Free Extra                 262144 @ 212074496 (128.0M)  Free space
/dev/sda7               Apple_HFS Leopard            314572800 @ 212336640 (150.0G)  HFS
/dev/sda8              Apple_Free Extra                 262144 @ 526909440 (128.0M)  Free space
/dev/sda9              Apple_Boot Apple Hardware Test    100898 @ 527171584 ( 49.3M)  Unknown
/dev/sda10             Apple_Free Extra                 262144 @ 527272482 (128.0M)  Free space
/dev/sda11        Apple_UNIX_SVR2 Linux Boot           2097152 @ 527534626 (  1.0G)  Linux native
/dev/sda12             Apple_Free Extra                 262144 @ 529631778 (128.0M)  Free space
/dev/sda13        Apple_UNIX_SVR2 Gentoo Linux       134217728 @ 529893922 ( 64.0G)  Linux native
/dev/sda14             Apple_Free Extra                 262144 @ 664111650 (128.0M)  Free space
/dev/sda15        Apple_UNIX_SVR2 Debian Linux       134217728 @ 664373794 ( 64.0G)  Linux native
/dev/sda16             Apple_Free Extra                 262144 @ 798591522 (128.0M)  Free space
/dev/sda17        Apple_UNIX_SVR2 Linux Local         71216270 @ 798853666 ( 34.0G)  Linux native
/dev/sda18             Apple_Free Extra                 262144 @ 870069936 (128.0M)  Free space
/dev/sda19        Apple_UNIX_SVR2 Linux swap          67108864 @ 870332080 ( 32.0G)  Linux native
/dev/sda20             Apple_Free Extra                 262144 @ 937440944 (128.0M)  Free space

Block size=512, Number of Blocks=937703088
DeviceType=0x0, DeviceId=0x0
root #parted /dev/sda print 
Model: ATA TOSHIBA-TR200 (scsi)
Disk /dev/sda: 480GB
Sector size (logical/physical): 512B/512B
Partition Table: mac
Disk Flags: 

Number  Start   End     Size    File system     Name                 Flags
 1      512B    32.8kB  32.3kB                  Apple
 3      134MB   1074MB  939MB   hfs             NewWorld Bootblock   boot
 5      1208MB  109GB   107GB   hfs+            Tiger
 7      109GB   270GB   161GB   hfs+            Leopard
 9      270GB   270GB   51.7MB  hfs+            Apple Hardware Test  boot
11      270GB   271GB   1074MB  ext2            Linux Boot
13      271GB   340GB   68.7GB  btrfs           Gentoo Linux
15      340GB   409GB   68.7GB  btrfs           Debian Linux
17      409GB   445GB   36.5GB  ext4            Linux Local
19      446GB   480GB   34.4GB  linux-swap(v1)  Linux swap

To make the Linux kernel recognize the new partitions a restart is required. But to get access to devices that were not in use, partprobe (from the sys-block/parted package) can force the kernel to re-read the partition table, with the exception of partitions already in use:

root #partprobe /dev/sda
Error: Partition(s) 11, 13, 17, 19 on /dev/sda have been written, but we have been unable to inform the kernel of the change, probably because it/they are in use.  As a result, the old partition(s) will remain in use.  You should reboot now before making further changes.

Notice that partition 11 is now /boot "Linux Boot" (ext2), but it was mounted as /dev/sda9 before the change to /dev/sda11. The former partition numbers and the listet new partition numbers from the partprobe error message should not be used for anything else than to keep them mounted as they were, but it should be safe to access the newly created NewWorld Bootblock as /dev/sda3 now to setup GRUB as the bootloader – before a restart.

CHRP boot script

Install the required tools:

root #emerge --ask sys-boot/grub sys-fs/hfsutils sys-apps/ibm-powerpc-utils

In this example, a CHRP boot script will load the GRUB image, which will use an initial grub.cfg to find and load the actual grub.cfg configuration from the /boot/grub directory on the Linux Boot /boot partition.

Make sure that /boot is mounted and create a new directory /boot/NWBB (for NewWorld BootBlock):

root #mount /boot
root #mkdir /boot/NWBB

Find out the UUID of the /boot partition:

root #cat /etc/fstab | grep /boot
UUID=be0188a5-1fd3-46fa-a82a-34cdea8ff194 /boot ext2 noauto,noatime,nodiratime,errors=remount-ro 1 2

Alternative:

root #cat /etc/fstab | grep /boot
/dev/sda11 /boot ext2 noauto,noatime,nodiratime,errors=remount-ro 1 2
root #blkid /dev/sda11
/dev/sda11: LABEL="Linux Boot" UUID="be0188a5-1fd3-46fa-a82a-34cdea8ff194" TYPE="ext2" PARTLABEL="Linux Boot"

Create file /boot/NWBB/grub-initial.cfg and use the UUID from above to let GRUB find the correct /boot partition. Although it would also be possible to specify an absolute path, using the UUID will compensate automatically for small changes, like switching drives or adding/deleting partitions.

FILE /boot/NWBB/grub-initial.cfg
search --no-floppy --fs-uuid --set=root be0188a5-1fd3-46fa-a82a-34cdea8ff194
set prefix=($root)/grub
configfile /grub/grub.cfg
Note
The UUID set via --set=root UUID is the UUID of the ext2 boot partition, not the root partition of the Linux base system. The real grub.cfg in /boot/grub/grub.cfg created by grub-mkconfig takes care of supplying the kernel cmdline with the real root UUID for booting Linux correctly.

Install GRUB to /boot/grub (the default path). Option --no-nvram prevents GRUB from setting the Open Firmware boot-device nvram variable. Since GRUB doesn't know about the CHRP script on the NewWorld Bootblock, it would set the wrong value anyway.

root #grub-install --target=powerpc-ieee1275 --no-nvram

With this setup, the initial grub.cfg (/boot/NWBB/grub-initial.cfg), GRUB will then look for /grub/grub.cfg on the actual /boot partition (i.e. /boot/grub/grub.cfg on the live system, since the boot partition is mounted) found via its UUID. Further updates to grub.cfg therefore go via the real grub.cfg the usual way, without the need to touch the NewWorld Bootblock anymore:

root #grub-mkconfig -o /boot/grub/grub.cfg

Now create a list of modules to be included in the GRUB image.

FILE /boot/NWBB/grub_mod-minimal.list
search_fs_uuid.mod search_fs_file.mod search_label.mod search.mod
part_apple.mod
fshelp.mod ext2.mod
halt.mod reboot.mod echo.mod

The command grub-mkimage will create a minimal grub bootimage that includes these modules and the initial grub.cfg:

root #grub-mkimage --prefix=/boot/grub --format=powerpc-ieee1275 --config=/boot/NWBB/grub-initial.cfg --output=/boot/NWBB/grub.img `cat /boot/NWBB/grub_mod-minimal.list`

If --config with grub-initial.cfg is ommited, it will be looked up as grub.cfg in the same directory where the grub.img will later be loaded on the NewWorld Bootblock HFS partition.

This /grub/grub.img bootloader can then be called from a CHRP boot script, which will enable easy selection. When turning on (or rebooting) the Power Mac, holding the ⌥/Option/Alt key right after the chime until the graphical boot selection appears, Open Firmware will show a list of all found operating systems with a compatible os-badge icon. Standard filenames for such a CHRP boot script are ofboot.b, which is used here, or bootinfo.txt. In reality the file name for the CHRP boot script does not matter as long as it is in XML format and the only blessed file on the partition. It may contain the following:

FILE /boot/NWBB/ofboot.bCHRP boot script
<CHRP-BOOT>
<COMPATIBLE>
MacRISC MacRISC3 MacRISC4
</COMPATIBLE>
<DESCRIPTION>
GRand Unified Bootloader
</DESCRIPTION>
<OS-NAME>
Linux
</OS-NAME>
<OS-BADGE-ICONS>
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</OS-BADGE-ICONS>
<BOOT-SCRIPT>
" screen" output
load-base release-load-area
boot &device;:&partition;,\grub\grub.img
</BOOT-SCRIPT>
</CHRP-BOOT>

If, for some reason, the boot instruction in the <BOOT-SCRIPT> section does not work, it is always possible to specify the boot partition directly.

Note
The <BOOT-SCRIPT> section of the CHRP boot script needs to be in Open Firmware syntax. For the boot command this is a device-specifier and arguments. The syntax is / component / component / ... name @ address : arguments. Arguments cannot contain / or @, hence the use of backslashes \ in the path. In order to use the current device, the &device; variable can be used, likewise &partition; for the current partition. The resulting &device;:&partition; contains the path where the CHRP script is loaded from. If the device-specifier doesn't start with a slash it is an alias, e.g. hd stands for the first internal disk drive. All available aliases are listed by the devalias command on the Open Firmware command prompt, which is loaded by holding ⌘ Cmd + ⌥ Option + O + F keys at the chime.

To find the partition number of the NewWorld Bootblock, simply translate the known Linux device path, e.g. /dev/sda3 is partition 3. In Open Firmware notation the command for the absolute path in the CHRP script would be boot hd:3,\grub\grub.img when the GRUB image is in /grub/grub.img and the HFS NewWorld Bootblock is the third partition on hd:, an alias for the first disk drive.

Note
The use of an absolute path has the disadvantage that it has to be changed in case the drive or the partition number changes for some reason. This would be the case if, for example, a second drive is installed and (due to the Open Firmware device lookup order) gets assigned the hd: alias, or if a partition is inserted before the NewWorld Bootblock and its partition number changes, resulting in a wrong path in the CHRP boot script. Booting GRUB would no longer work from the Open Firmware boot selection until the boot statement is changed to the new absolute path in the CHRP boot script. In such a case, GRUB can still be booted from the Open Firmware command prompt manually: should typing boot hd:3,\grub\grub.img instead of loading GRUB print an error message or load a different system, replacing the drive number and/or partition number could lead to a successful boot. For a second disk drive hd: may be replaced with hd1:, likewise the partition number after the colon.
FILE ofboot.bexample for using an absolute path in the CHRP boot script
<BOOT-SCRIPT>
boot hd:3,\grub\grub.img
</BOOT-SCRIPT>

Now copy all files to the NewWorld Bootblock HFS filesystem into /grub and bless (attribute :tbxi) the CHRP boot script ofboot.b and the /grub subdirectory:

root #hformat -l "NewWorld Bootblock" /dev/sda3
root #hmount /dev/sda3
root #hmkdir :grub
root #hcopy -r /boot/NWBB/grub-initial.cfg :grub:grub.cfg
root #hcopy -r /boot/NWBB/grub.img :grub:grub.img
root #hcopy -r /boot/NWBB/ofboot.b :grub:ofboot.b
root #hattrib -c UNIX -t tbxi :grub:ofboot.b
root #hattrib -b :grub
root #humount

Test and set as default boot-device

After a reboot, when holding the ⌥/Option/Alt key right after the chime, a startup selection for the partition with GRUB should now be visible. If everything worked, nvram from the sys-apps/ibm-powerpc-utils package may be used to set the default startup volume:

root #nvram --print-config | grep ^boot-device 
boot-device=first-boot/@0:5,\\:tbxi
root #nvram --update-config boot-device='first-boot/@0:3,\\:tbxi'

In the above commands the default startup volume was /dev/sda5 (in the example APM partition layout from above this is Tiger i.e. Mac OS X Tiger 10.4) and it is then set to /dev/sda3, the GRUB CHRP boot script in this example.

Note
Use the command nvram --print-config | grep ^boot-device to see how the default was set before. This information should be used to set the startup partition to the NewWorld Bootblock since most of the times only the partition number has to be changed. The above example is from a Power Mac G5, it may be different on other Macs. boot-device=hd:3,\\:tbxi should also work, as should boot-device=hd:3,\grub\ofboot.b and boot-device=hd:3,\grub\grub.img...

External resources

Retrieved from "https://wiki.gentoo.org/index.php?title=GRUB_on_Open_Firmware_(PowerPC)&oldid=1308670"