[PATCH] x86: insn decoder: create artificial 3rd byte for 2-byte VEX

[PATCH] x86: insn decoder: create artificial 3rd byte for 2-byte VEX

[Denys Vlasenko]

Before this patch, users need to do this to fetch vex.vvvv:

        if (insn->vex_prefix.nbytes == 2) {
                vex_vvvv = ((insn->vex_prefix.bytes[1] >> 3) & 0xf) ^ 0xf;
        }
        if (insn->vex_prefix.nbytes == 3) {
                vex_vvvv = ((insn->vex_prefix.bytes[2] >> 3) & 0xf) ^ 0xf;
        }

Make it so that insn->vex_prefix.bytes[2] always contains vex.wvvvvLpp bits.

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>
Cc: linux-kernel@vger.kernel.org
---

Masami, you were ok with this patch last time it was posted.
Can you "officially" add your Acked-By?

 arch/x86/lib/insn.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 54fcffe..829ca4c 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -163,6 +163,12 @@ found:
 				/* VEX.W overrides opnd_size */
 				insn->opnd_bytes = 8;
 		} else {
+			/*
+			 * For VEX2, fake VEX3-like byte#2.
+			 * Makes it easier to decode vex.W, vex.vvvv,
+			 * vex.L and vex.pp. Masking with 0x7f sets vex.W == 0.
+			 */
+			insn->vex_prefix.bytes[2] = b2 & 0x7f;
 			insn->vex_prefix.nbytes = 2;
 			insn->next_byte += 2;
 		}
-- 
1.8.1.4

Re: [PATCH] x86: insn decoder: create artificial 3rd byte for 2-byte VEX

[Masami Hiramatsu]

(2015/02/13 4:04), Denys Vlasenko wrote:
> Before this patch, users need to do this to fetch vex.vvvv:
> 
>         if (insn->vex_prefix.nbytes == 2) {
>                 vex_vvvv = ((insn->vex_prefix.bytes[1] >> 3) & 0xf) ^ 0xf;
>         }
>         if (insn->vex_prefix.nbytes == 3) {
>                 vex_vvvv = ((insn->vex_prefix.bytes[2] >> 3) & 0xf) ^ 0xf;
>         }
> 
> Make it so that insn->vex_prefix.bytes[2] always contains vex.wvvvvLpp bits.
> 
> Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>

Looks OK for me :)

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

BTW, where would you use this ??

> 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>
> Cc: linux-kernel@vger.kernel.org
> ---
> 
> Masami, you were ok with this patch last time it was posted.
> Can you "officially" add your Acked-By?
> 
>  arch/x86/lib/insn.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
> index 54fcffe..829ca4c 100644
> --- a/arch/x86/lib/insn.c
> +++ b/arch/x86/lib/insn.c
> @@ -163,6 +163,12 @@ found:
>  				/* VEX.W overrides opnd_size */
>  				insn->opnd_bytes = 8;
>  		} else {
> +			/*
> +			 * For VEX2, fake VEX3-like byte#2.
> +			 * Makes it easier to decode vex.W, vex.vvvv,
> +			 * vex.L and vex.pp. Masking with 0x7f sets vex.W == 0.
> +			 */
> +			insn->vex_prefix.bytes[2] = b2 & 0x7f;
>  			insn->vex_prefix.nbytes = 2;
>  			insn->next_byte += 2;
>  		}
> 


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

Re: [PATCH] x86: insn decoder: create artificial 3rd byte for 2-byte VEX

[Denys Vlasenko]

On Fri, Feb 13, 2015 at 1:32 PM, Masami Hiramatsu
<masami.hiramatsu.pt@hitachi.com> wrote:
> (2015/02/13 4:04), Denys Vlasenko wrote:
>> Before this patch, users need to do this to fetch vex.vvvv:
>>
>>         if (insn->vex_prefix.nbytes == 2) {
>>                 vex_vvvv = ((insn->vex_prefix.bytes[1] >> 3) & 0xf) ^ 0xf;
>>         }
>>         if (insn->vex_prefix.nbytes == 3) {
>>                 vex_vvvv = ((insn->vex_prefix.bytes[2] >> 3) & 0xf) ^ 0xf;
>>         }
>>
>> Make it so that insn->vex_prefix.bytes[2] always contains vex.wvvvvLpp bits.
>>
>> Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
>
> Looks OK for me :)
>
> Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
>
> BTW, where would you use this ??

arch/x86/kernel/uprobes.c

    reg2 = 0xff;        /* Fetch vex.vvvv */
    if (insn->vex_prefix.nbytes == 2)
        reg2 = insn->vex_prefix.bytes[1];
    else if (insn->vex_prefix.nbytes == 3)
        reg2 = insn->vex_prefix.bytes[2];


https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/arch/x86/kernel/uprobes.c#n354

[tip:x86/asm] x86/asm/decoder: Create artificial 3rd byte for 2-byte VEX

[tip-bot for Denys Vlasenko]

Commit-ID:  8a764a875fe3cf3a83296bacd00bfc41917e95e2
Gitweb:     http://git.kernel.org/tip/8a764a875fe3cf3a83296bacd00bfc41917e95e2
Author:     Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Thu, 12 Feb 2015 20:04:39 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 18 Feb 2015 21:01:50 +0100

x86/asm/decoder: Create artificial 3rd byte for 2-byte VEX

Before this patch, users need to do this to fetch vex.vvvv:

        if (insn->vex_prefix.nbytes == 2) {
                vex_vvvv = ((insn->vex_prefix.bytes[1] >> 3) & 0xf) ^ 0xf;
        }
        if (insn->vex_prefix.nbytes == 3) {
                vex_vvvv = ((insn->vex_prefix.bytes[2] >> 3) & 0xf) ^ 0xf;
        }

Make it so that insn->vex_prefix.bytes[2] always contains
vex.wvvvvLpp bits.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Frank Ch. Eigler <fche@redhat.com>
Cc: Jim Keniston <jkenisto@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1423767879-31691-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/lib/insn.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 1313ae6..5ea00dd 100644
--- a/arch/x86/lib/insn.c
+++ b/arch/x86/lib/insn.c
@@ -164,6 +164,12 @@ found:
 				/* VEX.W overrides opnd_size */
 				insn->opnd_bytes = 8;
 		} else {
+			/*
+			 * For VEX2, fake VEX3-like byte#2.
+			 * Makes it easier to decode vex.W, vex.vvvv,
+			 * vex.L and vex.pp. Masking with 0x7f sets vex.W == 0.
+			 */
+			insn->vex_prefix.bytes[2] = b2 & 0x7f;
 			insn->vex_prefix.nbytes = 2;
 			insn->next_byte += 2;
 		}