Booting the ELF kernel without ubldr on Raspberry Pi

[Tim Kientzle]

Actually, it would be more interesting to go a step further and boot the FreeBSD kernel directly from the firmware, bypassing both U-Boot and ubldr.

Warner did some work long ago to allow the FreeBSD kernel to boot from a Linux boot loader, which should make this possible.  You might try looking at that code and seeing if you can get it to work.

Cheers,

Tim


> On Dec 21, 2015, at 7:48 PM, Sylvain Garrigues <sylgar at gmail.com> wrote:
> 
> Hello,
> 
> I’d like to boot FreeBSD directly with u-boot, without ubldr, using an image provided by the u-boot mkimage tool. The reason is simple: mkimage can deal with compressed kernels and will therefore speed my boot time. And I want to try it anyway, as it seems possible reading http://bsdcan.org/2008/schedule/attachments/49_2008_uboot_freebsd.pdf <http://bsdcan.org/2008/schedule/attachments/49_2008_uboot_freebsd.pdf> and various other 
> 
> Before going there and using an mkimage, I’d like to boot the kernel image just with the same bootelf version provided by the sysutils/u-boot-rpi2 port. It doesn’t display anything and crashes (I think I can see « illegal instruction » just before the board reboots). I don’t understand why, and this is my first question.
> 
> Then I looked at the mkimage utility, although we can specify and freebsd kernel type through the -O flag, the bootm command only understands linux and NetBSD. I guess I should use linux there?
> 
> Thanks for your help,
> Sylvain
> 
> 
> PS: FYI, below is:
> 
> 1/ info about my kernel (I can see the entry point is at 0xc0100100), copied into the fat partition
> 
> # readelf -h /root/crochet/work/obj/arm.armv6/root/crochet/src/sys/RPI2/kernel                          
> ELF Header:
>  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
>  Class:                             ELF32
>  Data:                              2's complement, little endian
>  Version:                           1 (current)
>  OS/ABI:                            UNIX - System V
>  ABI Version:                       0
>  Type:                              EXEC (Executable file)
>  Machine:                           ARM
>  Version:                           0x1
>  Entry point address:               0xc0100100
>  Start of program headers:          52 (bytes into file)
>  Start of section headers:          6235080 (bytes into file)
>  Flags:                             0x5000202, has entry point, Version5 EABI, <unknown>
>  Size of this header:               52 (bytes)
>  Size of program headers:           32 (bytes)
>  Number of program headers:         6
>  Size of section headers:           40 (bytes)
>  Number of section headers:         38
>  Section header string table index: 35
> [root at clad /usr/ports/sysutils/u-boot-rpi2]#  
> 
> 2/ the interesting part of my include/configs/rpi-common.h from u-boot:
> 
> #define CONFIG_EXTRA_ENV_SETTINGS \
>        ENV_DEVICE_SETTINGS \
>        "loadaddr=0x02000000\0" \
>        "Fatboot=" \
>          "env exists loaderdev || env set loaderdev ${fatdev}; " \
>          "echo Booting from: ${fatdev} ${bootfile}; " \
>          "fatload ${fatdev} ${loadaddr} ${bootfile} && bootelf ${loadaddr}; " \
>        "\0" \
>        "preboot=" \
>          "fdt addr 0x100; " \
>          "env set bootfile kernel; " \  
>          "env set fatdev 'mmc 0'; " \
>        "\0"
> #undef  CONFIG_BOOTCOMMAND
> #define CONFIG_BOOTCOMMAND     "run Fatboot"
> #undef  CONFIG_PREBOOT
> #define CONFIG_PREBOOT         "run preboot"
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