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

dvlasenk · Ingo Molnar · commit 8a764a875fe3 · 2015-02-18T21:01:50.000+01:00
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
@@ -164,6 +164,12 @@ void insn_get_prefixes(struct insn *insn)
 				/* 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;
 		}
