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Date: Sun, 18 May 2014 01:00:40 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To: Denys Vlasenko <dvlasenk@...hat.com>
Cc: linux-kernel@...r.kernel.org, "Frank Ch. Eigler" <fche@...hat.com>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
Oleg Nesterov <oleg@...hat.com>,
Andi Kleen <andi@...stfloor.org>,
Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 2/2] x86: extend insn decoder to understand xop and evex
prefixes
(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@...hat.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> Cc: Frank Ch. Eigler <fche@...hat.com>
> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
> Cc: Jim Keniston <jkenisto@...ux.vnet.ibm.com>
> Cc: Oleg Nesterov <oleg@...hat.com>
> Cc: Andi Kleen <andi@...stfloor.org>
> Cc: Ingo Molnar <mingo@...nel.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@...achi.com
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