# palo PA-RISC/Linux Boot Loader

## Building palo

If you are self hosted on PA-RISC/Linux you should already have palo on your system. Assuming you have apt configured you can always run "`apt update; apt install palo`" to obtain the latest released version. If you need to build palo yourself, especially if you are cross-compiling on x86, skip to the end of this document.

## Kernel Command Line

Palo's boot loader parses the kernel command line to determine which kernel to boot and optionally which ramdisk to load. Given a command line: '0/vmlinux ... initrd=0/ramdisk ...', palo uses '0/vmlinux' as the kernel file and '0/ramdisk' as the ramdisk file. Both names are composed of a partition number followed by a file path name within that partition. Partition number '0' is magic and refers to the kernel (ramdisk) you placed on the boot medium with '-k' ('-r'). The path name on the '0' partition is ignored, '0/vmlinux' and '0/xyzzy' work identically, but it's a good idea to be consistent with what you'll call kernels and ramdisks on an ext2/3/4 partition.

## Creating and Maintaining Bootable Disks

Partitioned media usually refers to disks, in this case disks partitioned by fdisk or a similar program. Normally your disk is properly initialized when you install PA-RISC Linux, but if you need to do it by hand here are some clues:

- Use fdisk or something to (re)partition the disk. When you are finished, the disk may need to have a partition of type "F0" somewhere in the first 2Gb. This is where the boot loader and an optional kernel and ramdisk will be stored, so make it big enough for that -- at least 4Mb (I like 8-16Mb). There must also be an ext2/3/4 partition within the first 2Gb where you'll store your Linux kernel.
- If fdisk created the first partition at sector 2048, which is usual for modern fdisk, you don't need a F0 partition, so set all partition types to 82 swap or 83 linux and palo will place the boot loader inside the disk label. You still need a /boot partition <2GB from the beginning of the disk formatted as ext2/3/4 where you keep your boot kernels and initial ramdisks.

- Use mke2fs and mkswap as usual.

- Mount the partition, copy your kernel and any other interesting files to it, unmount.

- Use palo to make the disk bootable:

      	$ palo \
      	     -c "5/vmlinux HOME=/" \
      	     -k path/to/vmlinux \
      	     -I /dev/your-disk

  On a self-hosted system, you can accomplish the same thing by placing the following into `/etc/palo.conf`:
      --commandline=5/vmlinux HOME=/
      --recoverykernel=/boot/vmlinux
      --init-partitioned=/dev/your-disk
  and running palo.

  -k path/to/vmlinux designates a kernel to be stored along with the boot loader in the "F0" partition. You can omit this if you want, since you'll usually be booting a kernel from an ext2/3/4 partition instead. I like to have a kernel there just in case the ext2/3/4 one is lost for some reason. I call it a recovery kernel.

  -c 5/vmlinux must be changed for your situation. The number, 5, is the partition number of your ext2/3/4 partition as reported by fdisk, the same number you use when you mounted the partition (e.g., "mount /dev/sdb5 /mnt"). "/vmlinux" is the path to your kernel executable within your ext2/3/4 partition. The special partition number "0" is used to load the "recovery" kernel which you placed into the "F0" partition with -k.

  -I /dev/your-disk tells palo to initialize the palo boot parameters on the drive rather than preserving any existing parameters.

  Use '`palo -?`' or '`palo --help`' for more information.

You now have a partitioned bootable disk, try it!

There is no need to run palo when you change the kernel in your ext2/3/4 partition because it is located dynamically by the palo boot loader when you boot. However there are probably some tasks which will again require palo.

Once you have a partitioned bootable disk, palo can be used to change the default command line or kernel or boot loader. The most common task is probably changing the "recovery" kernel:

The update (-U) feature is currently disabled, perhaps permanently. The usual method for maintaining your disk is to edit /etc/palo.conf and rerun palo.

    	./palo -k path/to/vmlinux -U /dev/your-disk

or command line:

    	./palo -c "new command line" -U /dev/your-disk

Which will normally be done in a self-hosted environment by editing /etc/palo.conf and re-running palo. Hopefully you won't need to use palo very often.

## Creating ISO9660 Bootable CD-ROMs

Bootable CDs are often used for installation. In short the process is:

1. Master your CD image but don't burn it. The image MUST contain the kernel(s), iplboot, and ramdisk file (if used).

2. Run palo to make the image bootable:

       	./palo  -k path/to/vmlinux \
       		-b iplboot \
       		-c '0/vmlinux ....' \
       		-C your-iso-image

   -C tells palo to prepare a CD-ROM image. 'iplboot' and 'path/to/vmlinux' must be exactly the same files (same contents) you previously copied into the future root file system or palo will fail. I usually point those paths at the exact files in the directory from which I mastered the CD just to be sure.

3. Burn the CD and boot it.

CD-ROM support at the moment is a bit of a hack. Here's how it works.

palo currently treats CD-ROM as an unpartitioned sequential medium like tape or bootp. Unlike other unpartitioned media, there is no room to store the kernel and bootloader (iplboot) near the start of the (ISO-standard) medium, so palo requires you to put those files into the ISO file system. HP boot firmware requires the boot loader (iplboot) to be a multiple of 2k in length and be stored contiguously on a 2k boundary. Luckily the ISO file system meets all these criteria except for the mod-2k length, which is achieved by padding iplboot. The palo bootloader (iplboot) requires the kernel to be stored contiguously (except when booting from ext2/3/4), and the ISO file system works well for this too.

When you run palo, it locates the boot loader and kernel (optionally ramdisk) files in the ISO file system by doing a raw search through the ISO image. That's why the files in the ISO file system, and those named on the palo command line must be identical. Once found, pointers to those files are stored in the appropriate places in the boot headers.

Ideally palo and the boot loader would both understand the ISO file system, but that'll take more investment than I'm interested in supplying. If anyone pursues this, note that I've had good luck leveraging code from aboot, one of the Alpha boot loaders. I recommend starting with the ISO code from aboot-0.6 or later.

It may be possible to place a MS-DOS partition table on a CD-ROM therefore having an "F0" partition as on a hard disk, but I don't feel confident this would be understandable by, say, a Windows box.

## Some Newer Features

During installation testing several annoyances were discovered which have been partly addressed by two new features:

1. HP machines can use either a serial or a graphics boot console. Palo now figures out which one you are using and adds the appropriate "console=" to the end of the boot command line. It is only added if you don't already have "console=" in your boot command line.

2. It would be nice to have a single bootable image, especially when using CD-ROM. This requires booting a 32-bit or 64-bit kernel as appropriate for the hardware. Palo can now place both a 32 and 64-bit kernel on sequential (or CD-ROM) media. Simply use the -k (or --recoverykernel) option twice, once for each kernel. The palo boot loader examines the kernel name, which on sequential&CD-ROM is often "0/vmlinux", and if it ends in "32" or "64" palo boots the requested kernel. However if the name does not end in "32" or "64", palo chooses a kernel based upon a recommendation by firmware, which is almost always the right thing. (Note that a 32-bit kernel will be chosen to a 64-bit one on hardware which can boot both. Change the kernel name to 0/vmlinux64 if you want to force a 64-bit kernel.)

## Original Goals

- #1 support target is PA/Linux on a disk by itself (another disk(s) may contain a standard HP-UX installation)
- #2 support target is PA/Linux with kernel on sequential media such as tape or tftp/bootp (or CD-ROM)
- #3 support target is PA/Linux kernel on HP-UX disk with second disk for PA/Linux file system. (NOTE this is currently impossible with the ELF32 compiler **This is now a non-goal** )
- Not a support target: dual-boot HP-UX/Linux systems with both Linux and HP-UX file systems on a single disk
- Possibility: write mnttab into palo so you can boot with "normal" path names on that machine. If palo knew where to find /etc/mnttab...

## Features

PA/Linux partitioned hard disks:

- can be read/written by current Linux boxes, expecially x86
- can be read/written by IA-64 Linux boxes
- are tolerated by IA-32 and IA-64 non-Linux boxes
- are not understood by the HP-UX secondary boot loader
- require no new disk partitioning tools

## Terminology

palo is two programs, a boot loader, which is loaded by the HP firmware into memory and then executed, and boot media management tool, which initializes and updates bootable media such as disks. The palo boot loader is stored in a file called iplboot. "IPL" is HP jargon for Initial Program Loader. It's mostly called "the palo boot loader" in this document.

The boot media management tool is called palo, just as on x86 the LILO boot media management tool is called lilo, though it's worth noting that palo doesn't usually need to be used every time you build a new kernel, as lilo does.

## Basic Media Format

Bootable PA/Linux disks combine a standard MS-DOS partition table with the data required for HP firmware to locate its boot loader, all within the first 512-byte "sector" of the disk. Here is the detailed layout of the first 512 bytes of the disk. Only these bytes can be depended upon! The term "IPL" means Initial Program Loader e.g., boot loader in HP-ese.

    	Offset (hex)		Contents	Why

    	0			0x80		These two bytes denote
    	1			0x00		a LIF volume to HP firmware

    	f0-f3			IPL_ADDR	disk offset to beginning
    						of boot "IPL" loader.  Must
    						not be zero.  Must be a
    						multiple of 2kbytes.
    						Big endian.

    	f4-f7			IPL_SIZE	Size of boot loader in bytes.
    						Must be a multiple of 2kbytes.
    						Big endian.

    	f8-f11			IPL_ENTRY	Offset from the beginning
    						of the boot loader to its
    						entry point.  This really
    						better be a multiple of 4bytes.
    						Big endian.

    	1b0-1ff			P-TABLE		DOS partition table, managed
    						by fdisk.

Information about the kernel, command line, and ramdisk, is sandwiched between the LIF magic number and the IPL_ADDR. Check out struct firstblock in `common.h` for the details. The boot program must be located within the first 2 Gb of the boot medium (a limitation of older machines, which might not be permanent).

palo works with both un-partitioned (usually sequential) media such as tapes, and partitioned (usually random-access) media such as disks. The media format for un-partitioned media is described first since it is a subset of the format for partitioned media. In the remaining discussion, the term sequential is synonymous with un-partitioned, and random-access is synonymous with partitioned media. This restriction is not present in the palo software however.

On unpartitioned media, the partition table shown in the previous figure is unused and set to values which will not be mistaken for a partition table. The boot loader program is stored starting at 2kbytes from the beginning of the medium and is followed by the kernel file and optional ramdisk file.

On partitioned media, which is usually random-access, for example disks, the boot loader program must be stored in an area protected from disk management software, and often cannot be located at the first 2kbyte boundary as on sequential media. palo therefore places the boot loader, and optionally a kernel and ramdisk, in a special partition, created by fdisk, of type F0. HP-UX firmware requires the boot program to be stored on the boot medium starting on a multiple of 2kbytes, whereas the F0 partition might start on a 512-byte sector boundary. The boot program starts within the F0 partition on the first 2k boundary, which may be up to 3 sectors from the start of the partition.

The format of the boot loader, kernel, and ramdisk are identical to the sequential case except that some padding is added in order that somewhat larger kernels and boot loaders can be added later without re-writing the rest of the F0 partition (this feature may not yet be supported by palo however).

On partitioned media, palo can load a kernel from any ext2/3/4-formatted partition which falls within the first 2G of the medium, in addition to having a "sequential" kernel, perhaps best seen as a recovery kernel, within the F0 partition.

## Really Building palo

In the source directory type 'make'. On x86 you will need the PA-RISC cross compilers installed and in your $PATH.

You can use "`make DESTDIR=/ install`" to install palo in the normal location. On x86 the cross compilers are usually in "`/opt/palinux`" so I use "`make DESTDIR=/opt/palinux install`". Note that the palo executable goes into "`DESTDIR/sbin`" which you may want to add to your $PATH.

Palo can also be built in the normal way as a Debian package though it cannot be cross-compiled as a Debian package.