From: Jan Beulich <jbeulich@suse.com>
Date: Mon, 12 Dec 2016 08:41:57 +0000 (+0100)
Subject: x86emul: use SrcEax/DstEax where suitable for string insns
X-Git-Tag: archive/raspbian/4.11.1-1+rpi1~1^2~66^2~3195
X-Git-Url: https://dgit.raspbian.org/%22http://www.example.com/cgi/success//%22http:/www.example.com/cgi/success/?a=commitdiff_plain;h=fd3656422f2dd3b8157907f4da9f239386621759;p=xen.git

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 a2e10ec6b5..c9d48feb77 100644
--- 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;