Re: [Qemu-devel] [PATCH] target-mips: Fix 32 bit mode (wrong size of physical addresses)

[Aurelien Jarno <aurelien@aurel32.net>]

On Sun, Mar 14, 2010 at 05:28:51PM +0100, Stefan Weil wrote:
> Paul Brook schrieb:
> >> Commit 30724e758a21ba9f807efafe268626bd479db9de breaks
> >> malta (and other) mips 32 bit emulation.
> >>
> >> Fixing the physical address size for 32 bit machines
> >> makes it work again.
> >
> >> -#define TARGET_PHYS_ADDR_SPACE_BITS 36
> >> +#define TARGET_PHYS_ADDR_SPACE_BITS 32
> >
> > This is almost certainly the wrong change.
> >
> > Paul
> 
> Yes, Aurelien already said this, too, and I agree that my patch
> fixes the problem but is the wrong solution.
> 
> The wrong part seems to be loading or starting of the elf kernel image:
> the "boot loader" jumps to a memory location which is filled with
> nops (0). Either the load address of the kernel code is wrong, or
> the boot loader jumps to the wrong address.
> 
> The problem is also malta specific - mips ar7 emulation works fine.
> I did not test the other mips machines, so I cannot say whether they
> have this problem, too (maybe yes because of code copy + paste).
> 

Yes, the problem is that load_elf() only support mangling the addresses
through an addend. This is not working on MIPS as the addend would be
different depending on the type of ELF kernel (32 or 64-bit). The
correct operation for MIPS is too mangle the upper bits to do a kseg0 ->
physical translation.

I am working on a patch, will post it later today.

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net