On 17/12/19 15:18, Alex Bennée wrote: > > Paolo Bonzini <pbonz...@redhat.com> writes: > >> On 17/12/19 14:42, Alex Bennée wrote: >>>> Why do you need to set exception_index to something other than -1 (using >>>> cpu_loop_exit_noexc for example)? >>> If there is no exception to process we won't exit the main loop which we >>> need to do if we want to wait until there is data to read. >> >> Okay. >> >>>> Using ->stop here is a bit weird, since ->stop is usually related to >>>> pause_all_vcpus. >>> >>> Arguably we could come up with a better API to cpu.c but this allows us >>> to use cpu_resume(c->sleeping_cpu) when waking up rather than hand >>> rolling our own wake-up mechanism. >> >> But we already have the right wake-up mechanism, which is >> cpu->halted/cpu_has_work. > > cpu_has_work is a guest function though and semihosting_console is a > common hw module. It can't peek into the guests internal state.
semihosting_console only needs to something like cpu_interrupt(cpu->stopped_cpu, CPU_INTERRUPT_SEMIHOST). (By the way, the stopped_cpu should probably be a list to mimic the condition variable---for example a GSList). > This all > comes back to cpu_thread_is_idle anyway in making our decision about if > we do or do not sleep on the halt_cond. > >> That also makes it possible to just use >> EXCP_HALTED instead of adding a new EXCP_BLOCKED. > > We can certainly use EXCP_HALTED but maybe come up with a common way of > entering the state? There seems to be a combination of messing around > with special interrupts and direct poking of cs->halted = 1 while > setting the exception. Maybe this could finally clear up the #if > defined(TARGET_I386) hacking in cpus.c? If you're talking accel/tcg/cpu-exec.c, that's different; the issue there is that x86 has a kind of warm reset pin that is not equivalent to cpu_reset. Removing that would only entail adding a new member function to CPUClass. Paolo
