File 24275-x86-emul-lzcnt.patch of Package xen

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File 24275-x86-emul-lzcnt.patch of Package xen (Revision 768cdc8a741dfb1acb12b9f33d93ddfd)

Currently displaying revision 768cdc8a741dfb1acb12b9f33d93ddfd , Show latest

# HG changeset patch
# User Jan Beulich <jbeulich@suse.com>
# Date 1322725849 -3600
# Node ID 76ea126f21724b72c120aff59460f7bbe9e6960d
# Parent  07cf778d517fdf661a34027af653a489489bf222
x86/emulator: properly handle lzcnt and tzcnt

These instructions are prefix selected flavors of bsf and bsr
respectively, and hence the presences of the F3 prefix must be handled
in the emulation code in order to avoid running into problems on newer
CPUs.

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -990,6 +990,9 @@ static bool_t vcpu_has(
     return rc == X86EMUL_OKAY;
 }
 
+#define vcpu_has_lzcnt() vcpu_has(0x80000001, ECX,  5, ctxt, ops)
+#define vcpu_has_bmi1()  vcpu_has(0x00000007, EBX,  3, ctxt, ops)
+
 #define vcpu_must_have(leaf, reg, bit) \
     generate_exception_if(!vcpu_has(leaf, reg, bit, ctxt, ops), EXC_UD, -1)
 #define vcpu_must_have_sse2() vcpu_must_have(0x00000001, EDX, 26)
@@ -4114,13 +4117,24 @@ x86_emulate(
         dst.val   = (uint8_t)src.val;
         break;
 
-    case 0xbc: /* bsf */ {
-        int zf;
+    case 0xbc: /* bsf or tzcnt */ {
+        bool_t zf;
         asm ( "bsf %2,%0; setz %b1"
               : "=r" (dst.val), "=q" (zf)
-              : "r" (src.val), "1" (0) );
+              : "r" (src.val) );
         _regs.eflags &= ~EFLG_ZF;
-        if ( zf )
+        if ( (rep_prefix == REPE_PREFIX) && vcpu_has_bmi1() )
+        {
+            _regs.eflags &= ~EFLG_CF;
+            if ( zf )
+            {
+                _regs.eflags |= EFLG_CF;
+                dst.val = op_bytes * 8;
+            }
+            else if ( !dst.val )
+                _regs.eflags |= EFLG_ZF;
+        }
+        else if ( zf )
         {
             _regs.eflags |= EFLG_ZF;
             dst.type = OP_NONE;
@@ -4128,13 +4142,28 @@ x86_emulate(
         break;
     }
 
-    case 0xbd: /* bsr */ {
-        int zf;
+    case 0xbd: /* bsr or lzcnt */ {
+        bool_t zf;
         asm ( "bsr %2,%0; setz %b1"
               : "=r" (dst.val), "=q" (zf)
-              : "r" (src.val), "1" (0) );
+              : "r" (src.val) );
         _regs.eflags &= ~EFLG_ZF;
-        if ( zf )
+        if ( (rep_prefix == REPE_PREFIX) && vcpu_has_lzcnt() )
+        {
+            _regs.eflags &= ~EFLG_CF;
+            if ( zf )
+            {
+                _regs.eflags |= EFLG_CF;
+                dst.val = op_bytes * 8;
+            }
+            else
+            {
+                dst.val = op_bytes * 8 - 1 - dst.val;
+                if ( !dst.val )
+                    _regs.eflags |= EFLG_ZF;
+            }
+        }
+        else if ( zf )
         {
             _regs.eflags |= EFLG_ZF;
             dst.type = OP_NONE;

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File 24275-x86-emul-lzcnt.patch of Package xen (Revision 768cdc8a741dfb1acb12b9f33d93ddfd)

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