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

Masami Hiramatsu
2015-02-13T12:52:40Z

(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@redhat.com>
> CC: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> CC: Ingo Molnar <mingo@kernel.org>
> CC: Oleg Nesterov <oleg@redhat.com>
> CC: linux-kernel@vger.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@hitachi.com