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Re: [Xen-devel] [PATCH 1/4] libx86: Introduce x86_cpuid_lookup_vendor()
- To: Jan Beulich <JBeulich@xxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 27 Mar 2019 15:10:15 +0000
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- Cc: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Wed, 27 Mar 2019 15:30:40 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 26/03/2019 14:39, Jan Beulich wrote:
>>>> On 26.03.19 at 15:23, <jgross@xxxxxxxx> wrote:
>> IMO especially in the CPUID case it is desirable to explicitly specify
>> the width of the data. Looking at nodes 0x80000002 and following this
>> should be rather clear (and I even think get_model_name() should be
>> modified to use a pointer to uint32_t instead of unsigned int). Using
>> a type with size >= 4 doesn't fit really well. You want size == 4.
> Why? Fixed width types only introduce unnecessary restrictions
> when wanting to re-use code in other environments. And I don't
> see why CPUID nodes 0x8000000[234] would be any better (or
> worse) as an example here. If anything they tell us that neither
> uint32_t nor unsigned int are right, and it should be char[4] or
> uint8_t[4] instead (depending on whether we want to tie
> ourselves to CHAR_BIT == 8, which clearly is more restrictive
> than sizeof(int) >= 4, but otoh is also less likely to get in the
> way).
The ABI of CPUID really is 2x uint32_t input, 4x uint32_t output.
It is only by current convention that the data is also valid ASCII, and
there is absolutely nothing which prevents a new vendor choosing to put
non-ASCII content in their id string. Given the recent developments
from China, I'm slightly surprised that we haven't seen any UTF-8 (or
UTF-16 for that matter) yet.
~Andrew
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