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[Qemu-devel] Endian and userspace issues

From: anarkhos
Subject: [Qemu-devel] Endian and userspace issues
Date: Tue, 4 Jan 2005 11:44:20 -0800

        I've read the technical documentation, but there are some issues left 
unanswered in my head. I have very little experience with the x86 ISA so please 
bear with me if I missed something obvious.

        The short version of this email is: 

Has anyone considered emulating little endian CPUs on big endian platforms by 
emulating a big endian version of the CPU? I believe VirtualPC 5 does this (not 
sure about 6). Obviously there is a speed advantage in doing this, but the 
other advantage lies in the ability for non-native little endian executables to 
call big endian libraries without having to swap bytes.

        I became interested in QEMU when a Darwin port was revealed. 
Unfortunately, user mode emulation isn't supported yet. However, even when it 
is, I don't think (as I understand it) it will allow non-native binaries (in 
either ELF or Mach-O format) to call native ones. I found it interesting the 
documentation touts that user mode emulation can run WINE, but the entire WINE 
set of libs would have to run under emulation.

        I understand that there is an inherent difficulty in that x86 
executables assume they are running in little endian mode (I call it mode since 
some CPUs can run in either), but if one wants to have a shared user space with 
one set of natively optimized libraries what better way to implement it? We 
would have faster linking and faster CPU emulation.

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