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Subject: Re: [RFC v2-fix-v1 1/1] x86/tdx: Add __tdx_module_call() and
 __tdx_hypercall() helper functions
To:     Sean Christopherson <seanjc@google.com>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Tony Luck <tony.luck@intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Raj Ashok <ashok.raj@intel.com>, linux-kernel@vger.kernel.org
References: <3a7c0bba-cc43-e4ba-f7fe-43c8627c2fc2@intel.com>
 <20210519055842.2048957-1-sathyanarayanan.kuppuswamy@linux.intel.com>
 <568d2929-f366-e3be-96f9-0bfa91991ef2@intel.com>
 <02e7b229-4b6f-c1c7-bb63-48e5e9eca5db@linux.intel.com>
 <YKVwjdspTazTXlam@google.com>
From:   Andi Kleen <ak@linux.intel.com>
Message-ID: <77545da6-d534-e4c2-a60b-085705e3f0b7@linux.intel.com>
Date:   Wed, 19 May 2021 13:49:00 -0700
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On 5/19/2021 1:09 PM, Sean Christopherson wrote:
> On Wed, May 19, 2021, Kuppuswamy, Sathyanarayanan wrote:
>> On 5/19/21 8:31 AM, Dave Hansen wrote:
>>> Was this "older compiler" argument really the reason?
>> It is a speculation. I haven't tried to reproduce it with old compiler. So
>> I have removed that point.
> It's not "older" compilers.  gcc does not support R8-R15 as input/output
> constraints,

Yes that's true, but they can be in clobbers. So it usually just needs a 
mov from the input arguments for output, or a mov to the output 
arguments for output.