KVM: x86 emulator: simplify rip relative decoding

rip relative decoding is relative to the instruction pointer of the next
instruction; by moving address adjustment until after decoding is complete,
we remove the need to determine the instruction size.
Signed-off-by: Avi Kivity <avi@qumranet.com>

arch/x86/kvm/x86_emulate.c

@@ -664,7 +664,7 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
 {
 	struct decode_cache *c = &ctxt->decode;
 	u8 sib;
-	int index_reg = 0, base_reg = 0, scale, rip_relative = 0;
+	int index_reg = 0, base_reg = 0, scale;
 	int rc = 0;
 
 	if (c->rex_prefix) {
@@ -754,7 +754,7 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
 				c->modrm_ea += c->regs[index_reg] << scale;
 		} else if ((c->modrm_rm & 7) == 5 && c->modrm_mod == 0) {
 			if (ctxt->mode == X86EMUL_MODE_PROT64)
-				rip_relative = 1;
+				c->rip_relative = 1;
 		} else
 			c->modrm_ea += c->regs[c->modrm_rm];
 		switch (c->modrm_mod) {
@@ -770,22 +770,6 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
 			break;
 		}
 	}
-	if (rip_relative) {
-		c->modrm_ea += c->eip;
-		switch (c->d & SrcMask) {
-		case SrcImmByte:
-			c->modrm_ea += 1;
-			break;
-		case SrcImm:
-			if (c->d & ByteOp)
-				c->modrm_ea += 1;
-			else
-				if (c->op_bytes == 8)
-					c->modrm_ea += 4;
-				else
-					c->modrm_ea += c->op_bytes;
-		}
-	}
 done:
 	return rc;
 }
@@ -1044,6 +1028,9 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 		break;
 	}
 
+	if (c->rip_relative)
+		c->modrm_ea += c->eip;
+
 done:
 	return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
 }

include/asm-x86/kvm_x86_emulate.h

@@ -134,6 +134,7 @@ struct decode_cache {
 	u8 modrm_reg;
 	u8 modrm_rm;
 	u8 use_modrm_ea;
+	bool rip_relative;
 	unsigned long modrm_ea;
 	void *modrm_ptr;
 	unsigned long modrm_val;