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SubjectRe: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces
On Mon 19.Oct'20 at 18:15:15 -0400, Arvind Sankar wrote:
>On Mon, Oct 19, 2020 at 02:17:50PM +0800, shuo.a.liu@intel.com wrote:
>> From: Shuo Liu <shuo.a.liu@intel.com>
>>
>> The Service VM communicates with the hypervisor via conventional
>> hypercalls. VMCALL instruction is used to make the hypercalls.
>>
>> ACRN hypercall ABI:
>> * Hypercall number is in R8 register.
>> * Up to 2 parameters are in RDI and RSI registers.
>> * Return value is in RAX register.
>>
>> Introduce the ACRN hypercall interfaces. Because GCC doesn't support R8
>> register as direct register constraints, use supported constraint as
>> input with a explicit MOV to R8 in beginning of asm.
>>
>> +static inline long acrn_hypercall0(unsigned long hcall_id)
>> +{
>> + long result;
>> +
>> + asm volatile("movl %1, %%r8d\n\t"
>> + "vmcall\n\t"
>> + : "=a" (result)
>> + : "ir" (hcall_id)
>
>Is the hypercall id an unsigned long (64 bits) or an unsigned int (32
>bits)? This will generate broken assembly if the "r" option is chosen,
>eg something like
> movl %rdi, %r8d

Yes, it can be an unsigned long. So do MOV explicitly.

asm volatile("movq %1, %%r8\n\t"
"vmcall\n\t"
: "=a" (result)
: "ir" (hcall_id)

Thanks

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