Re: [PATCH 2/2] x86: extend insn decoder to understand xop and evex prefixes

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

(2014/05/17 3:34), Denys Vlasenko wrote:
> Since xop and evex prefixes are extensions of vex mechanism,
> they have similar bit layouts, and they can never be combined
> (an instruction can have only one of them),
> (ab)use insn->vex_prefix to store data of xop and evex too.
> 
> Users will need to conditionalize on insn->vex_prefix.bytes[0]
> instead of insn->vex_prefix.nbytes if they want to determine
> which of vex(-like) prefixes are there.
> 
> Instead of adding more inattr bits for these prefixes, drop
> VEX inattr bits and use VEX opcode values directly to detect them.
> There is no point in having additional level of indirection here.
> (And we are close to running out of inattr bits for prefixes).

Thank you very much for trying this work :)
But sorry, Nak, I don't like to use the prefix byte directly.
I'd rather like to add additional inattr bits for them.
This is a drawback of what I've done by gen-insn-atter-x86.awk.
It is prefer that x86 instruction information should be hidden
in opcode map and awk decoder.

And also, we should expand x86-opcode-map.txt for new instructions.

> 
> Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Frank Ch. Eigler <fche@redhat.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Andi Kleen <andi@firstfloor.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> ---
>  arch/x86/include/asm/inat.h          | 14 -----------
>  arch/x86/include/asm/insn.h          |  6 +++++
>  arch/x86/lib/insn.c                  | 47 +++++++++++++++++++++++++-----------
>  arch/x86/lib/x86-opcode-map.txt      |  4 +--
>  arch/x86/tools/gen-insn-attr-x86.awk |  2 --
>  5 files changed, 41 insertions(+), 32 deletions(-)
> 
> diff --git a/arch/x86/include/asm/inat.h b/arch/x86/include/asm/inat.h
> index 74a2e31..5aa6c05 100644
> --- a/arch/x86/include/asm/inat.h
> +++ b/arch/x86/include/asm/inat.h
> @@ -45,9 +45,6 @@
>  #define INAT_PFX_ADDRSZ	11	/* 0x67 */
>  /* x86-64 REX prefix */
>  #define INAT_PFX_REX	12	/* 0x4X */
> -/* AVX VEX prefixes */
> -#define INAT_PFX_VEX2	13	/* 2-bytes VEX prefix */
> -#define INAT_PFX_VEX3	14	/* 3-bytes VEX prefix */
>  
>  #define INAT_LSTPFX_MAX	3
>  #define INAT_LGCPFX_MAX	11
> @@ -138,17 +135,6 @@ static inline int inat_last_prefix_id(insn_attr_t attr)
>  		return attr & INAT_PFX_MASK;
>  }
>  
> -static inline int inat_is_vex_prefix(insn_attr_t attr)
> -{
> -	attr &= INAT_PFX_MASK;
> -	return attr == INAT_PFX_VEX2 || attr == INAT_PFX_VEX3;
> -}
> -
> -static inline int inat_is_vex3_prefix(insn_attr_t attr)
> -{
> -	return (attr & INAT_PFX_MASK) == INAT_PFX_VEX3;
> -}
> -
>  static inline int inat_is_escape(insn_attr_t attr)
>  {
>  	return attr & INAT_ESC_MASK;
> diff --git a/arch/x86/include/asm/insn.h b/arch/x86/include/asm/insn.h
> index 48eb30a..e098fec 100644
> --- a/arch/x86/include/asm/insn.h
> +++ b/arch/x86/include/asm/insn.h
> @@ -83,6 +83,12 @@ struct insn {
>  #define X86_REX_X(rex) ((rex) & 2)
>  #define X86_REX_B(rex) ((rex) & 1)
>  
> +/* VEX and VEX-like multi-byte prefixes */
> +#define X86_BYTE_VEX3  0xc4
> +#define X86_BYTE_VEX2  0xc5
> +#define X86_BYTE_XOP   0x8f
> +#define X86_BYTE_EVEX  0x62
> +
>  /* VEX bit flags  */
>  #define X86_VEX_W(vex)	((vex) & 0x80)	/* VEX3 Byte2 */
>  #define X86_VEX_R(vex)	((vex) & 0x80)	/* VEX2/3 Byte1 */
> diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
> index 829ca4c..2351977 100644
> --- a/arch/x86/lib/insn.c
> +++ b/arch/x86/lib/insn.c
> @@ -138,31 +138,34 @@ found:
>  	}
>  	insn->rex_prefix.got = 1;
>  
> -	/* Decode VEX prefix */
> +	/* Decode VEX prefixes et al. Layouts are:
> +	 * vex2:     c5    rvvvvLpp
> +	 * vex3/xop: c4/8f rxbmmmmm wvvvvLpp
> +	 * evex:     62    rxbR00mm wvvvv1pp zllBVaaa
> +	 */
>  	b = peek_next(insn_byte_t, insn);
> -	attr = inat_get_opcode_attribute(b);
> -	if (inat_is_vex_prefix(attr)) {
> +	if (b == X86_BYTE_VEX2 || b == X86_BYTE_VEX3 ||
> +	    b == X86_BYTE_EVEX ||
> +	    b == X86_BYTE_XOP) {
>  		insn_byte_t b2 = peek_nbyte_next(insn_byte_t, insn, 1);
> -		if (!insn->x86_64) {
> +		/*
> +		 * XOP: If the modrm.reg bits are 000, it's POP reg/mem.
> +		 */
> +		if (b == X86_BYTE_XOP && X86_MODRM_REG(b2) == 0) {
> +			goto vex_end;
> +		}
> +		else if (!insn->x86_64) {
>  			/*
>  			 * In 32-bits mode, if the [7:6] bits (mod bits of
>  			 * ModRM) on the second byte are not 11b, it is
> -			 * LDS or LES.
> +			 * LDS, LES or BOUND.
>  			 */
>  			if (X86_MODRM_MOD(b2) != 3)
>  				goto vex_end;
>  		}
>  		insn->vex_prefix.bytes[0] = b;
>  		insn->vex_prefix.bytes[1] = b2;
> -		if (inat_is_vex3_prefix(attr)) {
> -			b2 = peek_nbyte_next(insn_byte_t, insn, 2);
> -			insn->vex_prefix.bytes[2] = b2;
> -			insn->vex_prefix.nbytes = 3;
> -			insn->next_byte += 3;
> -			if (insn->x86_64 && X86_VEX_W(b2))
> -				/* VEX.W overrides opnd_size */
> -				insn->opnd_bytes = 8;
> -		} else {
> +		if (b == X86_BYTE_VEX2) {
>  			/*
>  			 * For VEX2, fake VEX3-like byte#2.
>  			 * Makes it easier to decode vex.W, vex.vvvv,
> @@ -171,7 +174,23 @@ found:
>  			insn->vex_prefix.bytes[2] = b2 & 0x7f;
>  			insn->vex_prefix.nbytes = 2;
>  			insn->next_byte += 2;
> +			goto vex_end;
> +		}
> +		b2 = peek_nbyte_next(insn_byte_t, insn, 2);
> +		insn->vex_prefix.bytes[2] = b2;
> +		if (insn->x86_64 && X86_VEX_W(b2)) {
> +			/* VEX.W overrides opnd_size */
> +			insn->opnd_bytes = 8;
> +		}
> +		if (b == X86_BYTE_VEX3 || b == X86_BYTE_XOP) {
> +			insn->vex_prefix.nbytes = 3;
> +			insn->next_byte += 3;
> +			goto vex_end;
>  		}
> +		b2 = peek_nbyte_next(insn_byte_t, insn, 3);
> +		insn->vex_prefix.bytes[3] = b2;
> +		insn->vex_prefix.nbytes = 4;
> +		insn->next_byte += 4;
>  	}
>  vex_end:
>  	insn->vex_prefix.got = 1;
> diff --git a/arch/x86/lib/x86-opcode-map.txt b/arch/x86/lib/x86-opcode-map.txt
> index 1a2be7c..9d8a964 100644
> --- a/arch/x86/lib/x86-opcode-map.txt
> +++ b/arch/x86/lib/x86-opcode-map.txt
> @@ -137,7 +137,7 @@ AVXcode:
>  # 0x60 - 0x6f
>  60: PUSHA/PUSHAD (i64)
>  61: POPA/POPAD (i64)
> -62: BOUND Gv,Ma (i64)
> +62: BOUND Gv,Ma (i64) | EVEX+3byte (Prefix)
>  63: ARPL Ew,Gw (i64) | MOVSXD Gv,Ev (o64)
>  64: SEG=FS (Prefix)
>  65: SEG=GS (Prefix)
> @@ -184,7 +184,7 @@ AVXcode:
>  8c: MOV Ev,Sw
>  8d: LEA Gv,M
>  8e: MOV Sw,Ew
> -8f: Grp1A (1A) | POP Ev (d64)
> +8f: Grp1A (1A) | POP Ev (d64) | XOP+2byte (Prefix)
>  # 0x90 - 0x9f
>  90: NOP | PAUSE (F3) | XCHG r8,rAX
>  91: XCHG rCX/r9,rAX
> diff --git a/arch/x86/tools/gen-insn-attr-x86.awk b/arch/x86/tools/gen-insn-attr-x86.awk
> index 093a892..b2db5ad 100644
> --- a/arch/x86/tools/gen-insn-attr-x86.awk
> +++ b/arch/x86/tools/gen-insn-attr-x86.awk
> @@ -93,8 +93,6 @@ BEGIN {
>  	prefix_num["SEG=GS"] = "INAT_PFX_GS"
>  	prefix_num["SEG=SS"] = "INAT_PFX_SS"
>  	prefix_num["Address-Size"] = "INAT_PFX_ADDRSZ"
> -	prefix_num["VEX+1byte"] = "INAT_PFX_VEX2"
> -	prefix_num["VEX+2byte"] = "INAT_PFX_VEX3"
>  
>  	clear_vars()
>  }
> 


-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com