Re: [PATCH v2 4/5] system/vl: Restrict icount to TCG emulation

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 7/12/23 23:38, Richard Henderson wrote:
> On 12/7/23 07:45, Philippe Mathieu-Daudé wrote:
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>> ---
>>   stubs/icount.c | 6 ------
>>   system/vl.c    | 6 +++++-
>>   2 files changed, 5 insertions(+), 7 deletions(-)
>>
>> diff --git a/stubs/icount.c b/stubs/icount.c
>> index a5202e2dd9..b060b03a73 100644
>> --- a/stubs/icount.c
>> +++ b/stubs/icount.c
>> @@ -1,5 +1,4 @@
>>   #include "qemu/osdep.h"
>> -#include "qapi/error.h"
>>   #include "sysemu/cpu-timers.h"
>>   /* icount - Instruction Counter API */
>> @@ -10,11 +9,6 @@ void icount_update(CPUState *cpu)
>>   {
>>       abort();
>>   }
>> -void icount_configure(QemuOpts *opts, Error **errp)
>> -{
>> -    /* signal error */
>> -    error_setg(errp, "cannot configure icount, TCG support not 
>> available");
>> -}
>>   int64_t icount_get_raw(void)
>>   {
>>       abort();
>> diff --git a/system/vl.c b/system/vl.c
>> index 2bcd9efb9a..8c99c5f681 100644
>> --- a/system/vl.c
>> +++ b/system/vl.c
>> @@ -2270,7 +2270,11 @@ static void user_register_global_props(void)
>>   static int do_configure_icount(void *opaque, QemuOpts *opts, Error 
>> **errp)
>>   {
>> -    icount_configure(opts, errp);
>> +    if (tcg_enabled()) {
>> +        icount_configure(opts, errp);
>> +    } else {
>> +        error_setg(errp, "cannot configure icount, TCG support not 
>> available");
>> +    }
>>       return 0;
>>   }
> 
> This is called before the accelerator is chosen -- even before the set 
> of available accelerators is even found.  Indeed, that's the very next 
> thing that configure_accelerators does.
> 
> OTOH, I don't see why icount_configure is being called so early.

See commit 7f8b6126e7:

     vl: move icount configuration earlier

     Once qemu_tcg_configure is turned into a QOM property setter,
     it will not be able to set a default value for mttcg_enabled.
     Setting the default will move to the TCG instance_init function,
     which currently runs before "-icount" is processed.

     However, it is harmless to do configure_icount for all accelerators;
     we will just fail later if a non-TCG accelerator is selected.  So do
     that.

But few commits after we have 28a0961757 ("vl: merge -accel processing
into configure_accelerators"), so it shouldn't be an issue now. I'll
consolidate.