Am 23.11.2011 22:59, schrieb Richard Henderson: > On 11/20/2011 12:51 PM, Andreas Färber wrote: >> * Part of the problem is that common CPUState fields are not at the >> start of the struct. I have therefore been playing with a >> CPU_COMMON_PREFIX at the start of the struct and using a macro for >> clearing on reset, which preserves part of the common prefix fields. > > Most of the RISC hosts have a limited displacement in their load and > store instructions. E.g. 14 bits for Sparc, 12 bits for ARM, 10. > We want to be able to load and store the target cpu registers very > efficiently. > > If you move all the common fields to the beginning, that will include > the (rather large) TLB tables, and overflow those small offsets. > > This change would almost certainly be a Large Mistake.
Then what is your suggestion? Today, common code is accessing env-> struct members directly for icount, TLB, etc. If they're at the end of the struct, offsets vary and we can't cast to a common-subset struct. Anthony's qom-upstream.4 branch doesn't seem to touch CPUState yet. Having an empty C++ base class with virtual, non-implemented accessor methods that are implemented for each arch is the only solution I can think of other than "proxy" functions with large switches based on a common (=prefixed) type field. Andreas
