Re: all class init functions for all types in QEMU are called in select_machine(). Expected?

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/03/21 14:40, Claudio Fontana wrote:
>      /*
>       * double dispatch. The first callback allows the accel cpu
>       * to run initializations for the CPU,
>       * the second one allows the CPU to customize the accel cpu
>       * behavior according to the CPU.
>       *
>       * The second is currently only used by TCG, to specialize the
>       * TCGCPUOps depending on the CPU type.
>       */
>      cc->accel_cpu = accel_cpu;
>      if (accel_cpu->cpu_class_init) {
>          accel_cpu->cpu_class_init(cc);
>      }
>      if (cc->init_accel_cpu) {
>          cc->init_accel_cpu(accel_cpu, cc);
>      }
> }
> 
> .. but maybe this is premature, and should wait for actual users of this beyond TCG on ARM?

I prefer to single out TCG and have the call in cpu_class_init.  The 
idea of double dispatch (as opposed to an if/else chain with checks on 
the class of the argument) is that the first caller uses different 
"method names" to tell its type name to the target.

See for example 
https://en.wikipedia.org/wiki/Double_dispatch#Example_in_Ruby.

Paolo