x86_emulate: PUSH <mem> must read source operand just once

... for the case of accessing MMIO.

Rather than doing the early operand type adjustment for just for that
case, do it for all of the 0xF6, 0xF7, and 0xFF groups (allowing some
other code to be dropped instead).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

xen/arch/x86/x86_emulate/x86_emulate.c

@@ -1632,6 +1632,41 @@ x86_emulate(
     if ( override_seg != -1 )
         ea.mem.seg = override_seg;
 
+    /* Early operand adjustments. */
+    if ( !twobyte )
+        switch ( b )
+        {
+        case 0xf6 ... 0xf7: /* Grp3 */
+            switch ( modrm_reg & 7 )
+            {
+            case 0 ... 1: /* test */
+                d = (d & ~SrcMask) | SrcImm;
+                break;
+            case 4: /* mul */
+            case 5: /* imul */
+            case 6: /* div */
+            case 7: /* idiv */
+                d = (d & (ByteOp | ModRM)) | DstImplicit | SrcMem;
+                break;
+            }
+            break;
+        case 0xff: /* Grp5 */
+            switch ( modrm_reg & 7 )
+            {
+            case 2: /* call (near) */
+            case 4: /* jmp (near) */
+            case 6: /* push */
+                if ( mode_64bit() && op_bytes == 4 )
+                    op_bytes = 8;
+                /* fall through */
+            case 3: /* call (far, absolute indirect) */
+            case 5: /* jmp (far, absolute indirect) */
+                d = DstNone|SrcMem|ModRM;
+                break;
+            }
+            break;
+        }
+
     /* Decode and fetch the source operand: register, memory or immediate. */
     switch ( d & SrcMask )
     {
@@ -3318,16 +3353,6 @@ x86_emulate(
         switch ( modrm_reg & 7 )
         {
         case 0 ... 1: /* test */
-            /* Special case in Grp3: test has an immediate source operand. */
-            src.type = OP_IMM;
-            src.bytes = (d & ByteOp) ? 1 : op_bytes;
-            if ( src.bytes == 8 ) src.bytes = 4;
-            switch ( src.bytes )
-            {
-            case 1: src.val = insn_fetch_type(int8_t);  break;
-            case 2: src.val = insn_fetch_type(int16_t); break;
-            case 4: src.val = insn_fetch_type(int32_t); break;
-            }
             goto test;
         case 2: /* not */
             dst.val = ~dst.val;
@@ -3336,12 +3361,11 @@ x86_emulate(
             emulate_1op("neg", dst, _regs.eflags);
             break;
         case 4: /* mul */
-            src = dst;
             dst.type = OP_REG;
             dst.reg  = (unsigned long *)&_regs.eax;
             dst.val  = *dst.reg;
             _regs.eflags &= ~(EFLG_OF|EFLG_CF);
-            switch ( src.bytes )
+            switch ( dst.bytes = src.bytes )
             {
             case 1:
                 dst.val = (uint8_t)dst.val;
@@ -3377,12 +3401,11 @@ x86_emulate(
             }
             break;
         case 5: /* imul */
-            src = dst;
             dst.type = OP_REG;
             dst.reg  = (unsigned long *)&_regs.eax;
             dst.val  = *dst.reg;
             _regs.eflags &= ~(EFLG_OF|EFLG_CF);
-            switch ( src.bytes )
+            switch ( dst.bytes = src.bytes )
             {
             case 1:
                 dst.val = ((uint16_t)(int8_t)src.val *
@@ -3419,10 +3442,10 @@ x86_emulate(
             break;
         case 6: /* div */ {
             unsigned long u[2], v;
-            src = dst;
+
             dst.type = OP_REG;
             dst.reg  = (unsigned long *)&_regs.eax;
-            switch ( src.bytes )
+            switch ( dst.bytes = src.bytes )
             {
             case 1:
                 u[0] = (uint16_t)_regs.eax;
@@ -3469,10 +3492,10 @@ x86_emulate(
         }
         case 7: /* idiv */ {
             unsigned long u[2], v;
-            src = dst;
+
             dst.type = OP_REG;
             dst.reg  = (unsigned long *)&_regs.eax;
-            switch ( src.bytes )
+            switch ( dst.bytes = src.bytes )
             {
             case 1:
                 u[0] = (int16_t)_regs.eax;
@@ -3564,20 +3587,13 @@ x86_emulate(
             emulate_1op("dec", dst, _regs.eflags);
             break;
         case 2: /* call (near) */
+            dst.val = _regs.eip;
+            _regs.eip = src.val;
+            src.val = dst.val;
+            goto push;
+            break;
         case 4: /* jmp (near) */
-            if ( (dst.bytes == 4) && mode_64bit() )
-            {
-                dst.bytes = op_bytes = 8;
-                if ( dst.type == OP_REG )
-                    dst.val = *dst.reg;
-                else if ( (rc = read_ulong(dst.mem.seg, dst.mem.off,
-                                           &dst.val, 8, ctxt, ops)) != 0 )
-                    goto done;
-            }
-            src.val = _regs.eip;
-            _regs.eip = dst.val;
-            if ( (modrm_reg & 7) == 2 )
-                goto push; /* call */
+            _regs.eip = src.val;
             dst.type = OP_NONE;
             break;
         case 3: /* call (far, absolute indirect) */
@@ -3610,21 +3626,7 @@ x86_emulate(
             break;
         }
         case 6: /* push */
-            /* 64-bit mode: PUSH defaults to a 64-bit operand. */
-            if ( mode_64bit() && (dst.bytes == 4) )
-            {
-                dst.bytes = 8;
-                if ( dst.type == OP_REG )
-                    dst.val = *dst.reg;
-                else if ( (rc = read_ulong(dst.mem.seg, dst.mem.off,
-                                           &dst.val, 8, ctxt, ops)) != 0 )
-                    goto done;
-            }
-            if ( (rc = ops->write(x86_seg_ss, sp_pre_dec(dst.bytes),
-                                  &dst.val, dst.bytes, ctxt)) != 0 )
-                goto done;
-            dst.type = OP_NONE;
-            break;
+            goto push;
         case 7:
             generate_exception_if(1, EXC_UD, -1);
         default: