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Date: Sun, 23 Apr 2006 23:48:47 +0100
From: Thiemo Seufer <ths@networkno.de>
Subject: Re: [Qemu-devel] new MIPS instructions
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To: Dirk Behme <dirk.behme@googlemail.com>
Cc: qemu-devel@nongnu.org

Dirk Behme wrote:
[snip]
> Pro "additional parameter": FPU is a good example for this. 
> If the processor I want to emulate has no FPU I would assume 
> if my code uses (accidently?)  FPU instructions I get 
> exception/error/warning from QEMU. It confused me that QEMU 
> (wrongly) executes my program with unsupported instructions 
> (architecture) without any warning.

In the long term we want both, I think, but ATM enhancing the emulation
capabilities has clearly priority for me.

We should probably go for a two-way approach: a per-ISA switch for
the userland emulation, and a per (generic-ish) CPU switch for
system emulation.

> I'm not an ELF expert: Does ELF contain information about 
> architecture compiled for? If yes, we can combine both ways 
> above? Load ELF file, read architecture from it and let QEMU 
> autoselect correct architecture features (or give error if 
> not supported). Then we have emulation accuracy but don't 
> need additional options.

Binutils adds usually header flags for the ISA, but it doesn't have to,
and the original ELF ABI mandates even the flags should be zero.

It doesn't cover FPU, and MIPS16 as only ASE AFAIR.


Thiemo