Re: [microblaze-uclinux] bootstrap code

[John Williams <jwilliams@xxxxxxxxxxxxxx>]

Hi Joszef,

Nice bit of code, and thanks very much for contributing it!  I put it 
into my system, put an elf image into the flash, and was booting the 
kernel in just a couple of minutes...

Comments for those who haven't tried this yet:

It's an elf loader, meaning that instead of using mb-objcopy -O binary 
image.elf image.bin, you just burn the raw elf file into the appropriate 
flash slot.  You need to run mb-strip on the elf image first to get rid 
of all the debugging strings - after strip the elf image is about the 
same size as the binary image (can even be smaller if there are large 
"zero" sections.

Joszef, as you say this could be suitable for the first step in the 3 
step boot process that is described in the Wiki.  There are two things I 
would need to change, one is critical, and the other just "nice to have"

The critical one is the same problem that most uClinux systems face with 
elf bootloaders.  That is, the romfs filesystem is copied into the 
kernel elf image (post-linking) with the following bit of shell script:

         mb-objcopy --add-section=.romfs=$(ROMFSIMG) \
           --adjust-section-vma=.romfs=$${ADDR} --no-adjust-warnings \
           --set-section-flags=.romfs=alloc,load,data   \
           $(ROOTDIR)/$(LINUXDIR)/linux $(ELFIMAGE)

I've never got a straight answer, but it's either a bug in objcopy, or a 
"bug" (feature?) in elf loaders, that this new romfs section is not 
allocated into a segment, and most elf loaders don't "see it".

The impact here is that when I booted a linux kernel with your 
bootloader, the kernel itself was fine, but there was no romfs file 
system, so we could not proceed to a shell etc.  Maybe someone with 
experience in uClinux bootloaders (david, greg? :) could comment on the 
tweak we should make to get the bootloader to see the .romfs section?

The "nice-to-have" would be to reduce the total size of the bootloader 
down to 2048 bytes, so we can squeeze it into a nice small BRAM block. 
If I can get around problem #1, then it should just be a matter of 
careful optimisation and removing some features and strings etc.

Once again, thanks very much for submitting it.  I think with a few 
small modifications it will be very useful indeed for the uClinux project.

Regards,

John
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