[LinuxBIOS] patch: extending LAR, and removing elf from linuxbios (it is not needed)
rminnich at gmail.com
Mon Aug 27 19:25:42 CEST 2007
don't get too scared about the subject line.
LAR is a very capable format. With two simple extensions, we can use
LAR to replace all that we are using ELF for now. This change can
really make life better:
1. we can use streaming decompress instead of the current "uncompress
elf to memory and then copy segments" approach. So we can get rid of
#define UNCOMPRESS_AREA (0x400000)
2. A simple lar l can show ALL segments, including payload segments
3. It's really easy to see where things will go in memory, and catch problems
4. We can figure out an ELF input file is bogus BEFORE we flash, not
AFTER we flash and try to boot it
5. did I mention streaming decompress?
6. We no longer have to worry about where we decompress the elf in
memory (this problem was causing trouble when the payload was a linux
kernel -- it was so big)
7. Since we have a load address, we can create this lar entry:
and specify that it be loaded at a place where linux will find it as
8. The decision on whether to XIP can be made in the LAR entry, not in
hardcode. For example, if initram needs to be XIP, set the load
address to 0xffffffff. Done.
The change is simple. Add a load address and entry point to the lar
header. Extend the lar tool to parse the elf file and create multiple
lar segments. It looks like this:
normal/payload0 (33192 bytes, lzma compressed to 18088 bytes @0x38
load @0x100000, entry 0x105258)
normal/payload1 (72 bytes, lzma compressed to 47 bytes @0x4718 load
@0x1225a0, entry 0x105258)
normal/option_table (932 bytes @0x4798 load @0, entry 0)
normal/stage2 (33308 bytes, lzma compressed to 15474 bytes @0x4b78
load @0, entry 0)
normal/initram (4208 bytes @0x8828 load @0, entry 0)
linuxbios.bootblock (16384 bytes @0xfc000 load @0, entry 0)
note that the payload is now payload0, payload1, etc. I've extended
linuxbios to look for these. Note that you can now see all the things
that get loaded ;they're no longer hidden in an ELF header somewhere.
Elf failures are gone!
Note that I've left legacy elf support in, for now, but recommend we
get rid of it as soon as possible.
patch attached. This is a first pass. lar.c needs some refactoring but
I want to get the comments going. You can now have a linux payload and
it will uncompress with no problems.
This has been tested with filo and BOCHS.
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