On 10/22/2009 12:22 PM, Carsten Otte wrote:
Avi Kivity wrote:
Right, but why? x86 qemu doesn't care about either pc or eflags
(with in-kernel irqchip, which s390 essentially is).
For different reasons. Most prominent for setting the condition code,
which is a sideband result of most instructions that indicates whether or
not the instruction actually worked - similar to the exception model in
high level programming languages.
Ok. Thanks for the explanation.
On x86 we avoid emulating instructions in userspace. Instead the kernel
requests userspace to do something (triggered by the instruction), and
the kernel does anything which might be implied by the instruction (like
copying the result into a register, or updating pc).
An example is port I/O. instead of userspace reading %edx to query the
port number and setting %eax to indicate the result, userspace reads a
port number struct field and writes an I/O result struct field. Only
the kernel accesses registers.
I don't know whether that model makes sense or not for s390, but please
consider it.
--
error compiling committee.c: too many arguments to function
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