[LinuxBIOS] ELF loader in v3

Patrick Georgi patrick at georgi-clan.de
Wed Jun 27 20:54:11 CEST 2007


I got quite far with adding decompression to lar (lzma'd data runs fine,
nrv2b decompression seems to hang), but ran into issues that need

Currently, two files in the lar archive are parsed directly out of rom
(using the find_file function which returns a pointer to there).
One of them is "option_table", a 900 byte file (which compresses to 350
or so), where I could live with it staying uncompressed in image.

The other one is the payload.

My current work around, is to just define a place in memory where to
decode it to and then load the ELF image from there.

This complicates ELF loading as now there is a risk that the raw ELF
file and the ELF image overlap. (Right now, I just use an address that I
know is beyond the ELF's range)

I propose a new API for the ELF loader that hides this issue and ensures
that decompression works fine. It would be used like this:
	copy_elf(&archive, "normal/payload", &entrypoint, &last_address)

This function looks up "normal/payload" in the archive starting at
archive, and returns success in the return value. entrypoint could then
be used to jump into the image. last_address contains the last byte used
by the ELF image.

The rationale for returning the entrypoint and last_address is to allow
further loads, so multipart payloads can be used, which provides a
cleaner and simpler way to allow modular payloads.
Specifically, I'd like to see this for the grub2 support I work on, as
it's very trivial to just push the modules as "payload.data" into the
lar archive, load it right behind the ELF image and have grub2 find its
modules at _end.

Patrick Georgi

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