linux-kernel - Re: [PATCH] x86: x86-opcode-map.txt: explain CALLW discrepancy between Intel and AMD

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Message-ID: <54DDF38F.6020002@hitachi.com>
Date:	Fri, 13 Feb 2015 21:52:31 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: x86-opcode-map.txt: explain CALLW discrepancy
 between Intel and AMD

(2015/02/13 4:06), Denys Vlasenko wrote:
> In 64-bit mode, AMD and Intel CPUs treat 0x66 prefix before branch
> insns differently. For near branches, it affects decode too since
> immediate offset's width is different.

You'd better add a link to your investigation report :)

http://marc.info/?l=linux-kernel&m=139714939728946&w=2

so that anyone can see what actually happens.

Thank you,

> 
> Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
> CC: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> CC: Ingo Molnar <mingo@...nel.org>
> CC: Oleg Nesterov <oleg@...hat.com>
> CC: linux-kernel@...r.kernel.org
> ---
>  arch/x86/lib/x86-opcode-map.txt | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/x86/lib/x86-opcode-map.txt b/arch/x86/lib/x86-opcode-map.txt
> index 1a2be7c..816488c 100644
> --- a/arch/x86/lib/x86-opcode-map.txt
> +++ b/arch/x86/lib/x86-opcode-map.txt
> @@ -273,6 +273,9 @@ dd: ESC
>  de: ESC
>  df: ESC
>  # 0xe0 - 0xef
> +# Note: "forced64" is Intel CPU behavior: they ignore 0x66 prefix
> +# in 64-bit mode. AMD CPUs accept 0x66 prefix, it causes RIP truncation
> +# to 16 bits. In 32-bit mode, 0x66 is accepted by both Intel and AMD.
>  e0: LOOPNE/LOOPNZ Jb (f64)
>  e1: LOOPE/LOOPZ Jb (f64)
>  e2: LOOP Jb (f64)
> @@ -281,6 +284,10 @@ e4: IN AL,Ib
>  e5: IN eAX,Ib
>  e6: OUT Ib,AL
>  e7: OUT Ib,eAX
> +# With 0x66 prefix in 64-bit mode, for AMD CPUs immediate offset
> +# in "near" jumps and calls is 16-bit. For CALL,
> +# push of return address is 16-bit wide, RSP is decremented by 2
> +# but is not truncated to 16 bits, unlike RIP.
>  e8: CALL Jz (f64)
>  e9: JMP-near Jz (f64)
>  ea: JMP-far Ap (i64)
> @@ -456,6 +463,7 @@ AVXcode: 1
>  7e: movd/q Ey,Pd | vmovd/q Ey,Vy (66),(v1) | vmovq Vq,Wq (F3),(v1)
>  7f: movq Qq,Pq | vmovdqa Wx,Vx (66) | vmovdqu Wx,Vx (F3)
>  # 0x0f 0x80-0x8f
> +# Note: "forced64" is Intel CPU behavior (see comment about CALL insn).
>  80: JO Jz (f64)
>  81: JNO Jz (f64)
>  82: JB/JC/JNAE Jz (f64)
> @@ -842,6 +850,7 @@ EndTable
>  GrpTable: Grp5
>  0: INC Ev
>  1: DEC Ev
> +# Note: "forced64" is Intel CPU behavior (see comment about CALL insn).
>  2: CALLN Ev (f64)
>  3: CALLF Ep
>  4: JMPN Ev (f64)
> 


-- 
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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