linux-kernel - Re: [PATCH] x86/asm: Add support for MOVDIR64B instruction

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Message-ID: <20190801194947.GA12033@agluck-desk2.amr.corp.intel.com>
Date:   Thu, 1 Aug 2019 12:49:48 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Alexey Dobriyan <adobriyan@...il.com>
Cc:     kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        jing.lin@...el.com, bp@...en8.de, x86@...nel.org
Subject: Re: [PATCH] x86/asm: Add support for MOVDIR64B instruction

On Thu, Aug 01, 2019 at 10:43:48PM +0300, Alexey Dobriyan wrote:
> > +static inline void movdir64b(void *dst, const void *src)
> > +{
> > +	/* movdir64b [rdx], rax */
> > +	asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02"
> > +			: "=m" (*(char *)dst)
>                                ^^^^^^^^^^
> 
> > +			: "d" (src), "a" (dst));
> > +}
> 
> Probably needs fake 64-byte type, so that compiler knows what is dirty.

Would that be something like this?

static inline void movdir64b(void *dst, const void *src)
{
	struct dstbytes {
		char pad[64];
	};

	/* movdir64b [rdx], rax */
	asm volatile(".byte 0x66, 0x0f, 0x38, 0xf8, 0x02"
		     : "=m" (*(struct dstbytes *)dst)
		     : "d" (src), "a" (dst));
}

Or did you have something else in mind?

-Tony