[OpenBIOS] Re : [PATCH 0/8] RFC: OFMEM cleanup/memory reduction patch
odanet at caramail.com
Sat Apr 14 20:05:54 CEST 2012
>Interesting, can you tell more about this project? Did you also modify
>QEMU to emulate the HW setup?
The project is currently in stealth mode, so I can't give any details for now.
>We should try to isolate the dependencies for QEMU, even if QEMU is
>probably the most interesting use case for OpenBIOS these days. Could
>you tell more about those bugs and even better, publish your changes?
A few issues :
- arch/sparc32/wuf.S : WIM register updates must not be immediately
followed by instructions depending on WIM value (SparcV8, §B.29, page 133) :
wr %twin_tmp1, 0x0, %wim /* Make window 'I' invalid */
restore %g0, %g0, %g0 /* Restore to window 'O' */
- arc/sparc32/entry.S : The FP (frame ptr) register is never initialised.
Registers are not initialized after a RESET (SparcV8, page 75).
- arch/sparc32/entry.S : MMU activation is written as :
set highmem, %g2
set 1, %g1
sta %g1, [%g0] ASI_M_MMUREGS ! enable mmu
It doesn't work because there is no precise synchronisation between
MMU registers updates and instruction fetches (because of pipelining)
MMU activation must be done in a area where virtual and physical adresses
are equal ( VA=FF00_0000 --> PA=F_FF00_0000 ).
The intial page table is modified to add this mapping and the activation
sequence is :
- jump from 0_ to F_something (PROM boot mode)
- activate the MMU
- plenty of NOPs
- jump to "highmem"
I also eventually disassembled Sun ROMs, and found sequences like that :
I can post patches, but they won't change anything to QEMU (at best).
The currently used version of OpenBIOS isn't the latest (SVN 1046), I
may need to do some cleanup.
(...and sorry for the previous message's bad formatting)
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