[coreboot] Fwd: fixed-location entities in cbfs.
rminnich at gmail.com
Thu Jun 4 21:52:12 CEST 2009
weird. That's the second time google has dropped an attachment on the
floor for me ...
---------- Forwarded message ----------
From: ron minnich <rminnich at gmail.com>
Date: Thu, Jun 4, 2009 at 12:29 PM
Subject: fixed-location entities in cbfs.
To: coreboot <coreboot at coreboot.org>
Attached are what I view as a transition plan for cbfs to implement
cbfs files at fixed addresses.
I call this transitional as the approach I am taking is to add
capability to cbfstool but not change code in a way that will break
There is one additional command syntax, so, example:
cbfstool add rom romstrap optionrom 0xffffd000
Will add the file to that fix location for a romstrap.
The assumption is that the ROM is based at the end of a 32-bit address
space. As you can see from the code, that assumption can easily be
over-ridden, if we ever need to, with a command option.
Here is one example output result.
rminnich at xcpu2:~/src/bios/coreboot-v2/util/cbfstool$ ./cbfstool x.cbf print
x.cbf: 1024 kB, bootblocksize 32768, romsize 1048576, offset 0x0
Alignment: 16 bytes
Name Offset Type Size
h 0x0 optionrom 251
0x130 free 917120
h3 0xdffe0 optionrom 251
0xe0110 free 97960
The way this is implemented is pretty simple. I introduce a new
operator, split, that splits an unallocated area into two unallocated
areas. Then, allocation merely becomes a matter of 0, 1, or 2 splits:
0 split -- the free area is the exact fit
1 splits -- need to split some off the front or back
2 splits -- need to split off BOTH the front and back
I think you'll be able to see what I've done. I call this transitional
because, in the end state, we only need one allocate function; for now
I've left two in, to make sure I don't break compatibilty.
Why I like this better than ldscript approach: I like having the
ROMSTRAP located by cbfs, not linker scripts. For one thing, it makes
romstrap visible as a first class object. I think I would have latched
onto a problem I was having much more quickly had I remembered the
ROMSTRAP. It gets lost in the linker scripts.
Anywhere, here it is.This will allow us to remove a lot of ldscript trickiness.
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