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Sender: Arvind Sankar <niveditas98@gmail.com>
From:   Arvind Sankar <nivedita@alum.mit.edu>
Date:   Mon, 19 Oct 2020 18:15:15 -0400
To:     shuo.a.liu@intel.com
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Subject: Re: [PATCH v5 04/17] x86/acrn: Introduce hypercall interfaces
Message-ID: <20201019221515.GA2875488@rani.riverdale.lan>
References: <20201019061803.13298-1-shuo.a.liu@intel.com>
 <20201019061803.13298-5-shuo.a.liu@intel.com>
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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

> +		     : "r8", "memory");
> +
> +	return result;
> +}
> +
> +static inline long acrn_hypercall1(unsigned long hcall_id,
> +				   unsigned long param1)
> +{
> +	long result;
> +
> +	asm volatile("movl %1, %%r8d\n\t"
> +		     "vmcall\n\t"
> +		     : "=a" (result)
> +		     : "ir" (hcall_id), "D" (param1)
> +		     : "r8", "memory");
> +
> +	return result;
> +}
> +
> +static inline long acrn_hypercall2(unsigned long hcall_id,
> +				   unsigned long param1,
> +				   unsigned long param2)
> +{
> +	long result;
> +
> +	asm volatile("movl %1, %%r8d\n\t"
> +		     "vmcall\n\t"
> +		     : "=a" (result)
> +		     : "ir" (hcall_id), "D" (param1), "S" (param2)
> +		     : "r8", "memory");
> +
> +	return result;
> +}
> +
>  #endif /* _ASM_X86_ACRN_H */
> -- 
> 2.28.0
>