[PATCH] x86emul: convert op_bytes/opc checks in SIMD emulation

[Jan Beulich]

Delivering #UD for an internal shortcoming of the emulator isn't quite
right. Similarly BUG() is bigger a hammer than needed.

Switch to using EXPECT() instead.

Suggested-by: Andrew Cooper <andrew.coop...@citrix.com>
Signed-off-by: Jan Beulich <jbeul...@suse.com>

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -8114,13 +8114,13 @@ x86_emulate(
     }
     else if ( state->simd_size != simd_none )
     {
-        generate_exception_if(!op_bytes, X86_EXC_UD);
         generate_exception_if((vex.opcx && (d & TwoOp) &&
                                (vex.reg != 0xf || (evex_encoded() && 
!evex.RX))),
                               X86_EXC_UD);
 
-        if ( !opc )
-            BUG();
+        EXPECT(op_bytes);
+        EXPECT(opc);
+
         if ( evex_encoded() )
         {
             opc[insn_bytes - EVEX_PFX_BYTES] = 0xc3;