x86emul: use SrcEax/DstEax where suitable for string insns

LODS, SCAS, and STOS all use the accumulator as one of their operands.
This avoids some open coding of things, but requires switching around
operands of SCAS.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index a2e10ec6b5f5a97d64557f2c4eafe4213890e506..c9d48feb7782d709e2a6b067a3d0aa0d30fdf187 100644 (file)
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -135,9 +135,9 @@ static const opcode_desc_t opcode_table[256] = {
     ByteOp|ImplicitOps, ImplicitOps,
     /* 0xA8 - 0xAF */
     ByteOp|DstEax|SrcImm, DstEax|SrcImm,
-    ByteOp|ImplicitOps|Mov, ImplicitOps|Mov,
-    ByteOp|ImplicitOps|Mov, ImplicitOps|Mov,
-    ByteOp|ImplicitOps, ImplicitOps,
+    ByteOp|DstImplicit|SrcEax|Mov, DstImplicit|SrcEax|Mov,
+    ByteOp|DstEax|SrcImplicit|Mov, DstEax|SrcImplicit|Mov,
+    ByteOp|DstImplicit|SrcEax, DstImplicit|SrcEax,
     /* 0xB0 - 0xB7 */
     ByteOp|DstReg|SrcImm|Mov, ByteOp|DstReg|SrcImm|Mov,
     ByteOp|DstReg|SrcImm|Mov, ByteOp|DstReg|SrcImm|Mov,
@@ -3239,15 +3239,15 @@ x86_emulate(
     case 0xaa ... 0xab: /* stos */ {
         unsigned long nr_reps = get_rep_prefix(false, true);
 
-        dst.bytes = (d & ByteOp) ? 1 : op_bytes;
+        dst.bytes = src.bytes;
         dst.mem.seg = x86_seg_es;
         dst.mem.off = truncate_ea(_regs.edi);
         if ( (nr_reps == 1) || !ops->rep_stos ||
-             ((rc = ops->rep_stos(&_regs.eax,
+             ((rc = ops->rep_stos(&src.val,
                                   dst.mem.seg, dst.mem.off, dst.bytes,
                                   &nr_reps, ctxt)) == X86EMUL_UNHANDLEABLE) )
         {
-            dst.val = _regs.eax;
+            dst.val = src.val;
             dst.type = OP_MEM;
             nr_reps = 1;
         }
@@ -3262,9 +3262,6 @@ x86_emulate(
 
     case 0xac ... 0xad: /* lods */
         get_rep_prefix(true, false);
-        dst.type  = OP_REG;
-        dst.bytes = (d & ByteOp) ? 1 : op_bytes;
-        dst.reg   = (unsigned long *)&_regs.eax;
         if ( (rc = read_ulong(ea.mem.seg, truncate_ea(_regs.esi),
                               &dst.val, dst.bytes, ctxt, ops)) != 0 )
             goto done;
@@ -3277,16 +3274,15 @@ x86_emulate(
         unsigned long next_eip = _regs.eip;
 
         get_rep_prefix(false, true);
-        src.bytes = dst.bytes = (d & ByteOp) ? 1 : op_bytes;
-        dst.val = _regs.eax;
         if ( (rc = read_ulong(x86_seg_es, truncate_ea(_regs.edi),
-                              &src.val, src.bytes, ctxt, ops)) != 0 )
+                              &dst.val, src.bytes, ctxt, ops)) != 0 )
             goto done;
         register_address_increment(
             _regs.edi, (_regs.eflags & EFLG_DF) ? -src.bytes : src.bytes);
         put_rep_prefix(1);
-        /* cmp: dst - src ==> src=*%%edi,dst=%%eax ==> %%eax - *%%edi */
-        emulate_2op_SrcV("cmp", src, dst, _regs.eflags);
+        /* cmp: %%eax - *%%edi ==> src=%%eax,dst=*%%edi ==> src - dst */
+        dst.bytes = src.bytes;
+        emulate_2op_SrcV("cmp", dst, src, _regs.eflags);
         if ( (repe_prefix() && !(_regs.eflags & EFLG_ZF)) ||
              (repne_prefix() && (_regs.eflags & EFLG_ZF)) )
             _regs.eip = next_eip;