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>

diff --git a/arch/x86/lib/insn.c b/arch/x86/lib/insn.c
index 1313ae6b478b6c439741ee032a8c33b86868ee2c..5ea00ddc18251ecb4821a904a060c136d9fa7a1a 100644 (file)
--- 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;
                }