====== How-to loader.o to preform a kexec like operations ======

loader.o allow you to run a custom kernel, without the danger of having to reprogram your Flash ROM. It loads a new kernel into memory and jumps to it directly.

===== Compiling loader.o =====

  - Get [[http://www.genbako.com/loader.o/org/loader.tar.gz|loader.o original source]] and optionally [[http://www.genbako.com/loader.o/loader.diff|patch for initrd problem]].
  - [[:howto:kernel_build#build_toolchain|Build a toolchain for cross compiling]].
  - In Makefile point ''INCLUDE = -isystem'' parameter to a **2.4.21-pre4** kernel header files!
  - Fix ''gcc'' and ''ld'' entry in Makefile to meet your cross compiled toolchain.
  - Apply initrd patch if you like.
  - Run ''make''

===== Use pre-compiled loader.o =====
If you think that compiling loader.o by yourself is too much hassle then you can use a [[http://dns323.kood.org/downloads/people/sala/loader.o|pre-compiled loader.o]]

===== Preparing proper kernel image for loading =====
For kernel building instructions look [[howto:kernel_build|kernel building wiki page]].

Before you start compiling kernel you should apply this patch, which is going to fix [[http://dns323.kood.org/forum/t850-building-kernel-loadero.html|memory detection problem]].
<code patch>
--- arch/ppc/platforms/sandpoint_setup.c.orig	2007-08-09 18:02:58.000000000 -0400
+++ arch/ppc/platforms/sandpoint_setup.c	2007-08-09 18:03:41.000000000 -0400
@@ -451,8 +451,8 @@
 
 	/* This might be fixed in DINK32 12.4, or we'll have another
 	 * way to determine the correct memory size anyhow. */
-	/* return mpc10x_get_mem_size(MPC10X_MEM_MAP_B); */
-	return 16*1024*1024;
+	return mpc10x_get_mem_size(MPC10X_MEM_MAP_B);
+	/*return 16*1024*1024;*/
 }
 
 static void __init
</code>
If you would like to use custom cmdline parameter for your kernel, for example "root=/dev/sda3" then you will also need this patch:
  - Search for "#endif /* CONFIG_BLK_DEV_INITRD */" in arch/ppc/platform/sandpoint_setup.c
  - Add following lines after "#endif /* CONFIG_BLK_DEV_INITRD */" line:
<code>        if ( r6 )
        {
               *(char *)(r7+KERNELBASE) = 0;
               strcpy(cmd_line, (char *)(r6+KERNELBASE));
        }
</code>
After you have successfully built a kernel image you should note that the loader need the kernel to be in binary format. It can be done with powerpc-linux-objcopy command.
<code>powerpc-linux-objcopy -O binary vmlinux</code>

===== Using loader.o to load a kernel image =====
<code>sync;insmod /mnt/HD_a2/loader.o kernel=/mnt/HD_a2/vmlinux</code>
or
<code>sync;insmod /mnt/HD_a2/loader.o kernel=/mnt/HD_a2/vmlinux cmdline="root=/dev/sda3"</code>

===== Use pre-compiled vmlinux =====
Pre-compiled vmlinux is available at [[http://dns323.kood.org/downloads/people/sala/vmlinux|here]].
It does support custom cmdline parameter. I does have usb and usb storage modules built in, <del>so it is possible to load operating system from usb stick</del>. This kernel image is optimized to boot [[:howto:chroot_gentoo|Gentoo linux]]. .config is available at [[http://dns323.kood.org/downloads/people/sala/loader.config|here]].\\
<del>To load from usb stick:</del>
<code>sync;insmod /mnt/HD_a2/loader.o kernel=/mnt/HD_a2/vmlinux cmdline="root=/dev/sdb1"</code>