From c2c4303a07ae20af5268b08f673263102454b97e Mon Sep 17 00:00:00 2001
From: Gabe Black <gabe.black@gmail.com>
Date: Fri, 14 Jan 2022 00:15:21 -0800
Subject: [PATCH] arch-x86: Use 16 bit modRM encoding if address size is 16
 bit.

The modRM byte should be interpreted with 16 bit rules if the address
size is 16 bits, whether that's because the address size is that by
default, or because it was overridden. It should not be based on the
operand size in any case.

Change-Id: I8827abe1eea8905b0404f7402fb9531804d63fae
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55503
Maintainer: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
---
 src/arch/x86/decoder.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/arch/x86/decoder.cc b/src/arch/x86/decoder.cc
index 842e0ad3fb..4c798721b0 100644
--- a/src/arch/x86/decoder.cc
+++ b/src/arch/x86/decoder.cc
@@ -515,7 +515,7 @@ Decoder::doModRMState(uint8_t nextByte)
     State nextState = ErrorState;
     ModRM modRM = nextByte;
     DPRINTF(Decoder, "Found modrm byte %#x.\n", nextByte);
-    if (defOp == 1) {
+    if (emi.addrSize == 2) {
         // Figure out 16 bit displacement size.
         if ((modRM.mod == 0 && modRM.rm == 6) || modRM.mod == 2)
             displacementSize = 2;