The previous check erroneously allowed CMP to be modified with LOCK.
Instead, tag explicitly the instructions that do support LOCK.

Acked-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 target/i386/tcg/decode-new.c.inc | 17 ++++++++++-------
 target/i386/tcg/decode-new.h     |  3 +++
 target/i386/tcg/emit.c.inc       |  5 -----
 3 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/target/i386/tcg/decode-new.c.inc b/target/i386/tcg/decode-new.c.inc
index 232c6a45c96..5eb2e9d0224 100644
--- a/target/i386/tcg/decode-new.c.inc
+++ b/target/i386/tcg/decode-new.c.inc
@@ -151,6 +151,7 @@
 
 #define cpuid(feat) .cpuid = X86_FEAT_##feat,
 #define xchg .special = X86_SPECIAL_Locked,
+#define lock .special = X86_SPECIAL_HasLock,
 #define mmx .special = X86_SPECIAL_MMX,
 #define zext0 .special = X86_SPECIAL_ZExtOp0,
 #define zext2 .special = X86_SPECIAL_ZExtOp2,
@@ -1103,10 +1104,6 @@ static int decode_modrm(DisasContext *s, CPUX86State *env, X86DecodedInsn *decod
 {
     int modrm = get_modrm(s, env);
     if ((modrm >> 6) == 3) {
-        if (s->prefix & PREFIX_LOCK) {
-            decode->e.gen = gen_illegal;
-            return 0xff;
-        }
         op->n = (modrm & 7);
         if (type != X86_TYPE_Q && type != X86_TYPE_N) {
             op->n |= REX_B(s);
@@ -1881,6 +1878,9 @@ static void disas_insn_new(DisasContext *s, CPUState *cpu, int b)
         if (decode.op[0].has_ea) {
             s->prefix |= PREFIX_LOCK;
         }
+        decode.e.special = X86_SPECIAL_HasLock;
+        /* fallthrough */
+    case X86_SPECIAL_HasLock:
         break;
 
     case X86_SPECIAL_ZExtOp0:
@@ -1909,6 +1909,12 @@ static void disas_insn_new(DisasContext *s, CPUState *cpu, int b)
         break;
     }
 
+    if (s->prefix & PREFIX_LOCK) {
+        if (decode.e.special != X86_SPECIAL_HasLock || !decode.op[0].has_ea) {
+            goto illegal_op;
+        }
+    }
+
     if (!validate_vex(s, &decode)) {
         return;
     }
@@ -1952,9 +1958,6 @@ static void disas_insn_new(DisasContext *s, CPUState *cpu, int b)
         gen_load_ea(s, &decode.mem, decode.e.vex_class == 12);
     }
     if (s->prefix & PREFIX_LOCK) {
-        if (decode.op[0].unit != X86_OP_INT || !decode.op[0].has_ea) {
-            goto illegal_op;
-        }
         gen_load(s, &decode, 2, s->T1);
         decode.e.gen(s, env, &decode);
     } else {
diff --git a/target/i386/tcg/decode-new.h b/target/i386/tcg/decode-new.h
index e6c904a3192..611bfddd957 100644
--- a/target/i386/tcg/decode-new.h
+++ b/target/i386/tcg/decode-new.h
@@ -158,6 +158,9 @@ typedef enum X86InsnCheck {
 typedef enum X86InsnSpecial {
     X86_SPECIAL_None,
 
+    /* Accepts LOCK prefix; LOCKed operations do not load or writeback operand 0 */
+    X86_SPECIAL_HasLock,
+
     /* Always locked if it has a memory operand (XCHG) */
     X86_SPECIAL_Locked,
 
diff --git a/target/i386/tcg/emit.c.inc b/target/i386/tcg/emit.c.inc
index d444d83e534..98c4c9569ef 100644
--- a/target/i386/tcg/emit.c.inc
+++ b/target/i386/tcg/emit.c.inc
@@ -55,11 +55,6 @@ static void gen_NM_exception(DisasContext *s)
     gen_exception(s, EXCP07_PREX);
 }
 
-static void gen_illegal(DisasContext *s, CPUX86State *env, X86DecodedInsn *decode)
-{
-    gen_illegal_opcode(s);
-}
-
 static void gen_load_ea(DisasContext *s, AddressParts *mem, bool is_vsib)
 {
     TCGv ea = gen_lea_modrm_1(s, *mem, is_vsib);
-- 
2.43.0