[Qemu-devel] [RFC PATCH] s390x-linux-user

[Ulrich Hecht <uli@suse.de>]

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Hi!

Here's an alpha of the S/390 target I'm currently working on. So far, 
only the s390x-linux-user target is supported. No machine emulation, no 
31-bit or 24-bit addressing modes. The S/390 instruction set is 
gargantuan, and I implement instructions as they come along, which means 
that everything not emitted by GCC (and then some) is unimplemented. 
Nonetheless, it runs dynamically linked binaries from SLE11 and most of 
the stuff in /bin, including bash and vim. (You wouldn't believe how 
many binaries there require 128-bit floats...)

Besides the unimplemented instructions, the code still leaves a lot of 
room for improvement, especially for optimization. All condition code 
computation, for instance, is currently done in helper functions.

There is a very peculiar S/390 instruction called "EXECUTE". What it does 
is to take another instruction stored somewhere in memory, logical-OR 
the second byte of the instruction with the LSB of R0 and then execute 
the result, without changing the instruction in memory or the program 
counter. Any idea how to implement this in QEMU? Currently, I'm 
interpreting the couple of instructions that GCC uses EXECUTE with, but 
in the long run that would amount to implementing a second emulator...

CU
Uli

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