On 25 January 2012 19:25, Xin Tong <xerox.time.t...@gmail.com> wrote: > as I mentioned. In my current implementation of coremu, the code could > be executed when it is modified. so the modifications need to be > atomic. I think I need a scratch area in which the restore_cpu_state > needs to be generated while leaving the already generated code in > tact. would this solve the problem ?
No, the code must be regenerated at the same absolute address, because the TCG code generation routines might otherwise produce different (different size!) output. Consider the case of a jump instruction, where for example on x86 we might generate a short or a longer instruction depending on how far the target was from where we were writing the code. It should be entirely fine to have code being executed while it is being "modified", because the cpu_restore_state can only ever write exactly identical bytes to memory that were there to start with, so there will never be an issue with a core executing code finding half an instruction, or with icache/dcache incoherence on architectures which need explicit cache maintenance (ie non-x86). -- PMM
