linux-kernel - Re: [PATCH 1/2] x86/cpu/vmware: Use the full form of INL in VMWARE

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Date:   Fri, 18 Oct 2019 09:33:10 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Thomas Hellström (VMware) 
        <thomas_os@...pmail.org>
Cc:     linux-kernel@...r.kernel.org,
        Thomas Hellstrom <thellstrom@...are.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        clang-built-linux@...glegroups.com,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86-ml <x86@...nel.org>,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 1/2] x86/cpu/vmware: Use the full form of INL in
 VMWARE_HYPERCALL

On Fri, Oct 18, 2019 at 03:40:51PM +0200, Thomas Hellström (VMware) wrote:
> From: Thomas Hellstrom <thellstrom@...are.com>
> 
> LLVM's assembler doesn't accept the short form INL instruction:
> 
>   inl (%%dx)
> 
> but instead insists on the output register to be explicitly specified.
> 
> This was previously fixed for the VMWARE_PORT macro. Fix it also for
> the VMWARE_HYPERCALL macro.
> 
> Fixes: b4dd4f6e3648 ("Add a header file for hypercall definitions")
> Suggested-by: Sami Tolvanen <samitolvanen@...gle.com>
> Signed-off-by: Thomas Hellstrom <thellstrom@...are.com>
> Cc: clang-built-linux@...glegroups.com
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: x86-ml <x86@...nel.org>
> Cc: Borislav Petkov <bp@...e.de>
> ---
>  arch/x86/include/asm/vmware.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/vmware.h b/arch/x86/include/asm/vmware.h
> index e00c9e875933..f5fbe3778aef 100644
> --- a/arch/x86/include/asm/vmware.h
> +++ b/arch/x86/include/asm/vmware.h
> @@ -29,7 +29,8 @@
>  
>  /* The low bandwidth call. The low word of edx is presumed clear. */
>  #define VMWARE_HYPERCALL						\
> -	ALTERNATIVE_2("movw $" VMWARE_HYPERVISOR_PORT ", %%dx; inl (%%dx)", \
> +	ALTERNATIVE_2("movw $" VMWARE_HYPERVISOR_PORT			\
> +		      ", %%dx; inl (%%dx), %%eax",			\

Why wrap in the middle of movw?  Wrapping between instructions or letting
the line poke out is more readable IMO, e.g.

	ALTERNATIVE_2("movw $" VMWARE_HYPERVISOR_PORT ", %%dx; "	\
		      "inl (%%dx), %%eax",				\

or

	ALTERNATIVE_2("movw $" VMWARE_HYPERVISOR_PORT ", %%dx; inl (%%dx), %%eax", \

>  		      "vmcall", X86_FEATURE_VMCALL,			\
>  		      "vmmcall", X86_FEATURE_VMW_VMMCALL)
>  
> -- 
> 2.21.0
>