From 8a764a875fe3cf3a83296bacd00bfc41917e95e2 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Thu, 12 Feb 2015 20:04:39 +0100 Subject: [PATCH] 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 Acked-by: Masami Hiramatsu Cc: Ananth N Mavinakayanahalli Cc: Frank Ch. Eigler Cc: Jim Keniston Cc: Oleg Nesterov Cc: Srikar Dronamraju Link: http://lkml.kernel.org/r/1423767879-31691-1-git-send-email-dvlasenk@redhat.com Signed-off-by: Ingo Molnar --- 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 1313ae6b478b..5ea00ddc1825 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; }