Re: [Qemu-devel] [PATCH 14/28] m68k: replace cpu_m68k_init() with cpu_generic_init()

[Igor Mammedov]

On Mon, 17 Jul 2017 17:05:15 +0200
Andreas Färber <address@hidden> wrote:

> Am 17.07.2017 um 12:41 schrieb Igor Mammedov:
> > On Sat, 15 Jul 2017 08:08:58 -1000
> > Richard Henderson <address@hidden> wrote:
> >   
> >> On 07/14/2017 03:52 AM, Igor Mammedov wrote:  
> >>> @@ -230,6 +230,8 @@ static void m68k_cpu_realizefn(DeviceState *dev, 
> >>> Error **errp)
> >>>       M68kCPUClass *mcc = M68K_CPU_GET_CLASS(dev);
> >>>       Error *local_err = NULL;
> >>>   
> >>> +    register_m68k_insns(&cpu->env);
> >>> +    
> >>
> >> I think it would make more sense to do this during m68k_tcg_init.
> >>  
> > it seems that m68k_cpu_initfn accesses 'env' via some global,
> > while cpu_mk68k_init() used to access concrete pointer of just created cpu,
> > 
> > how about moving register_m68k_insns() to m68k_cpu_initfn(), instead?
> > it should be equivalent to what cpu_mk68k_init() used to do.  
> 
> As a general note, realize should be re-entrant. Can't tell from the
> above diff whether that is the case here.
Looking at

void register_m68k_insns (CPUM68KState *env)                                    
 
{                                                                               
 
    /* Build the opcode table only once to avoid                                
 
       multithreading issues. */                                                
 
    if (opcode_table[0] != NULL) {                                              
 
        return;                                                                 
 
    }

it is save to use multiple times,

also looking further in it:

#define BASE(name, opcode, mask) \                                              
 
    register_opcode(disas_##name, 0x##opcode, 0x##mask)                         
 
#define INSN(name, opcode, mask, feature) do { \                                
 
    if (m68k_feature(env, M68K_FEATURE_##feature)) \                            
 
        BASE(name, opcode, mask); \                                             
 
    } while(0)                                                                  
 
    BASE(undef,     0000, 0000);                                                
 
    INSN(arith_im,  0080, fff8, CF_ISA_A);

INSN macro depends on enabled features, it might work with current code that
has no user settable features but it will break once that is available.

So I retract my suggestion to move register_m68k_insns() into m68k_cpu_initfn()
and keep it as it's in this patch (in m68k_cpu_realizefn()),
that way features theoretically set between initfn(and m68k_tcg_init) and 
realize() will
have effect on created cpu and we won't have to fix it in future.

> Regards,
> Andreas
>