x86/emul: Simplfy L{ES,DS,SS,FS,GS} handling

%ss, %fs and %gs can be calculated by directly masking the opcode.  %es and
%ds cant, but the calculation isn't hard.

Use seg rather than dst.val for storing the calculated segment, which is
appropriately typed.  Drop the sel local variable entirely and use dst.val
instead.  The mode_64bit() check can be repositioned and simplified to drop
the ext check.  Replace opencoding of X86EMUL_OKAY.

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

diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c
index 6313b57bf82c3a574c697660dd63380c5844ace6..f69decee10e94fd6b89c3644e71e5081954438c2 100644 (file)
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -3398,24 +3398,20 @@ x86_emulate(
         _regs.eip = dst.val;
         break;
 
-    case 0xc4: /* les */ {
-        unsigned long sel;
-        dst.val = x86_seg_es;
-    les: /* dst.val identifies the segment */
-        generate_exception_if(mode_64bit() && !ext, EXC_UD);
+    case 0xc4: /* les */
+    case 0xc5: /* lds */
+        generate_exception_if(mode_64bit(), EXC_UD);
+        seg = (b & 1) * 3; /* es = 0, ds = 3 */
+    les:
         generate_exception_if(src.type != OP_MEM, EXC_UD);
         if ( (rc = read_ulong(src.mem.seg, src.mem.off + src.bytes,
-                              &sel, 2, ctxt, ops)) != 0 )
+                              &dst.val, 2, ctxt, ops)) != X86EMUL_OKAY )
             goto done;
-        if ( (rc = load_seg(dst.val, sel, 0, NULL, ctxt, ops)) != 0 )
+        ASSERT(is_x86_user_segment(seg));
+        if ( (rc = load_seg(seg, dst.val, 0, NULL, ctxt, ops)) != X86EMUL_OKAY )
             goto done;
         dst.val = src.val;
         break;
-    }
-
-    case 0xc5: /* lds */
-        dst.val = x86_seg_ds;
-        goto les;
 
     case 0xc8: /* enter imm16,imm8 */ {
         uint8_t depth = imm2 & 31;
@@ -5274,21 +5270,15 @@ x86_emulate(
         break;
 
     case X86EMUL_OPC(0x0f, 0xb2): /* lss */
-        dst.val = x86_seg_ss;
+    case X86EMUL_OPC(0x0f, 0xb4): /* lfs */
+    case X86EMUL_OPC(0x0f, 0xb5): /* lgs */
+        seg = b & 7;
         goto les;
 
     case X86EMUL_OPC(0x0f, 0xb3): btr: /* btr */
         emulate_2op_SrcV_nobyte("btr", src, dst, _regs.eflags);
         break;
 
-    case X86EMUL_OPC(0x0f, 0xb4): /* lfs */
-        dst.val = x86_seg_fs;
-        goto les;
-
-    case X86EMUL_OPC(0x0f, 0xb5): /* lgs */
-        dst.val = x86_seg_gs;
-        goto les;
-
     case X86EMUL_OPC(0x0f, 0xb6): /* movzx rm8,r{16,32,64} */
         /* Recompute DstReg as we may have decoded AH/BH/CH/DH. */
         dst.reg   = decode_register(modrm_reg, &_regs, 0);