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Re: [PATCH v3 12/19] target/riscv: add KVM specific MISA properties


From: Andrew Jones
Subject: Re: [PATCH v3 12/19] target/riscv: add KVM specific MISA properties
Date: Sat, 24 Jun 2023 09:32:47 +0200

On Fri, Jun 23, 2023 at 11:14:45AM -0300, Daniel Henrique Barboza wrote:
> 
> 
> On 6/23/23 06:38, Andrew Jones wrote:
> > On Thu, Jun 22, 2023 at 10:56:53AM -0300, Daniel Henrique Barboza wrote:
> > ...
> > > +#define KVM_MISA_CFG(_bit, _reg_id) \
> > > +    {.offset = _bit, .kvm_reg_id = _reg_id}
> > > +
> > > +/* KVM ISA extensions */
> > > +static KVMCPUConfig kvm_misa_ext_cfgs[] = {
> > > +    KVM_MISA_CFG(RVA, KVM_RISCV_ISA_EXT_A),
> > > +    KVM_MISA_CFG(RVC, KVM_RISCV_ISA_EXT_C),
> > > +    KVM_MISA_CFG(RVD, KVM_RISCV_ISA_EXT_D),
> > > +    KVM_MISA_CFG(RVF, KVM_RISCV_ISA_EXT_F),
> > > +    KVM_MISA_CFG(RVH, KVM_RISCV_ISA_EXT_H),
> > > +    KVM_MISA_CFG(RVI, KVM_RISCV_ISA_EXT_I),
> > > +    KVM_MISA_CFG(RVM, KVM_RISCV_ISA_EXT_M),
> > > +};
> > > +
> > ...
> > > +static void kvm_riscv_add_cpu_user_properties(Object *cpu_obj)
> > > +{
> > > +    int i;
> > > +
> > > +    for (i = 0; i < ARRAY_SIZE(kvm_misa_ext_cfgs); i++) {
> > > +        KVMCPUConfig *misa_cfg = &kvm_misa_ext_cfgs[i];
> > > +        int bit = misa_cfg->offset;
> > > +
> > > +        misa_cfg->name = misa_ext_info_arr[bit].name;
> > > +        misa_cfg->description = misa_ext_info_arr[bit].description;
> > 
> > I'd prefer these be set by KVM_MISA_CFG(), since we can. No need to wait
> > until runtime if we can do it at compile-time.
> 
> The compiler will complain about "error: initializer element is not constant" 
> and
> the build will fail. This happens because, apparently, the compiler doesn't 
> see the
> imported array as a constant, regardless of the 'const' type.
>

You're right. Initialization the way I suggested only works when
everything is in the same source file. That's a pity. So we can
either manage it they way you've done here or the way you did
in a previous patch, which was to include the info array in each
source file by putting it in the header. I think I prefer the
approach you used in this version more though.

Thanks,
drew



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