diff -r a0ca00815cc4 -r 4f92469f5b1d src/arch/x86/linux/process.hh
--- a/src/arch/x86/linux/process.hh	Fri Sep 28 09:35:25 2012 -0400
+++ b/src/arch/x86/linux/process.hh	Mon Sep 24 17:15:57 2012 +0200
@@ -53,9 +53,14 @@
     static SyscallDesc syscallDescs[];
     static const int numSyscalls;
 
+    static const unsigned int gdt_user_cs; // Linux: GDT_ENTRY_DEFAULT_USER_CS
+    static const unsigned int gdt_user_ds; // Linux: GDT_ENTRY_DEFAULT_USER_DS
+
   public:
     /// Constructor.
     X86_64LinuxProcess(LiveProcessParams * params, ObjectFile *objFile);
+
+    void initState();
 };
 
 class I386LinuxProcess : public I386LiveProcess
@@ -65,9 +70,14 @@
     static SyscallDesc syscallDescs[];
     static const int numSyscalls;
 
+    static const unsigned int gdt_user_cs; // Linux: GDT_ENTRY_DEFAULT_USER_CS
+    static const unsigned int gdt_user_ds; // Linux: GDT_ENTRY_DEFAULT_USER_DS
+
   public:
     /// Constructor.
     I386LinuxProcess(LiveProcessParams * params, ObjectFile *objFile);
+
+    void initState();
 };
 
 } // namespace X86ISA
diff -r a0ca00815cc4 -r 4f92469f5b1d src/arch/x86/linux/process.cc
--- a/src/arch/x86/linux/process.cc	Fri Sep 28 09:35:25 2012 -0400
+++ b/src/arch/x86/linux/process.cc	Mon Sep 24 17:15:57 2012 +0200
@@ -48,12 +48,98 @@
 using namespace std;
 using namespace X86ISA;
 
+static
+void
+setSegmentEntry(SETranslatingPortProxy & vmem,
+                Addr gdt_start,
+                unsigned int entry,
+                const SegDescriptor &sdesc)
+{
+    vmem.write(gdt_start + entry * sizeof(uint64_t),
+               static_cast<uint64_t>(sdesc));
+}
+
+static
+void
+setDefaultSegments (SETranslatingPortProxy & vmem,
+                    Addr gdt_start,
+                    const unsigned int gdt_user_cs,
+                    const unsigned int gdt_user_ds,
+                    const bool long_mode)
+{
+    SegDescriptor user_cs = 0;
+    user_cs.baseHigh = 0;
+    user_cs.baseLow = 0;
+    user_cs.g = 1;
+    user_cs.d = 1;
+    user_cs.b = 1;
+    user_cs.l = long_mode ? 1 : 0;
+    user_cs.avl = 0;
+    user_cs.limitHigh = ~0;
+    user_cs.limitLow = ~0;
+    user_cs.p = 1;
+    user_cs.dpl = 3;
+    user_cs.s = 1;
+    user_cs.type.codeOrData = 1;
+    user_cs.type.c = 0;
+    user_cs.type.r = 1;
+    user_cs.type.a = 0;
+    setSegmentEntry(vmem, gdt_start, gdt_user_cs, user_cs);
+
+    SegDescriptor user_ds = 0;
+    user_ds.baseHigh = 0;
+    user_ds.baseLow = 0;
+    user_ds.g = 1;
+    user_ds.d = 1;
+    user_ds.b = 1;
+    user_ds.l = 0;
+    user_ds.avl = 0;
+    user_ds.limitHigh = ~0;
+    user_ds.limitLow = ~0;
+    user_ds.p = 1;
+    user_ds.dpl = 3;
+    user_ds.s = 1;
+    user_ds.type.codeOrData = 0;
+    user_ds.type.e = 0;
+    user_ds.type.w = 1;
+    user_ds.type.a = 0;
+    setSegmentEntry(vmem, gdt_start, gdt_user_ds, user_ds);
+}
+
+
+// Linux: include/asm-x86/segment.h (when !defined(CONFIG_X86_32))
+const unsigned int X86_64LinuxProcess::gdt_user_cs   = 6;
+const unsigned int X86_64LinuxProcess::gdt_user_ds   = 5;
+// NOTE: We're ignoring GDT_ENTRY_DEFAULT_USER32_CS as GEM5 will use
+//       I386LinuxProcess instead.
+
+
 X86_64LinuxProcess::X86_64LinuxProcess(LiveProcessParams * params,
         ObjectFile *objFile)
     : X86_64LiveProcess(params, objFile, syscallDescs, numSyscalls)
 {}
 
+void
+X86_64LinuxProcess::initState()
+{
+    this->X86_64LiveProcess::initState();
+    setDefaultSegments(initVirtMem, _gdtStart, gdt_user_cs, gdt_user_ds, true);
+}
+
+
+// Linux: include/asm-x86/segment.h (when defined(CONFIG_X86_32))
+const unsigned int I386LinuxProcess::gdt_user_cs = 14;
+const unsigned int I386LinuxProcess::gdt_user_ds = 15;
+
+
 I386LinuxProcess::I386LinuxProcess(LiveProcessParams * params,
         ObjectFile *objFile)
     : I386LiveProcess(params, objFile, syscallDescs, numSyscalls)
 {}
+
+void
+I386LinuxProcess::initState()
+{
+    this->I386LiveProcess::initState();
+    setDefaultSegments(initVirtMem, _gdtStart, gdt_user_cs, gdt_user_ds, false);
+}
diff -r a0ca00815cc4 -r 4f92469f5b1d src/arch/x86/process.hh
--- a/src/arch/x86/process.hh	Fri Sep 28 09:35:25 2012 -0400
+++ b/src/arch/x86/process.hh	Mon Sep 24 17:15:57 2012 +0200
@@ -100,7 +100,7 @@
 
       public:
         void argsInit(int intSize, int pageSize);
-        void initState();
+        virtual void initState();
 
         X86ISA::IntReg getSyscallArg(ThreadContext *tc, int &i);
         void setSyscallArg(ThreadContext *tc, int i, X86ISA::IntReg val);
@@ -124,7 +124,7 @@
 
       public:
         void argsInit(int intSize, int pageSize);
-        void initState();
+        virtual void initState();
 
         void syscall(int64_t callnum, ThreadContext *tc);
         X86ISA::IntReg getSyscallArg(ThreadContext *tc, int &i);
diff -r a0ca00815cc4 -r 4f92469f5b1d src/arch/x86/process.cc
--- a/src/arch/x86/process.cc	Fri Sep 28 09:35:25 2012 -0400
+++ b/src/arch/x86/process.cc	Mon Sep 24 17:15:57 2012 +0200
@@ -205,12 +205,14 @@
             tc->setMiscRegNoEffect(MISCREG_SEG_BASE(seg), 0);
             tc->setMiscRegNoEffect(MISCREG_SEG_EFF_BASE(seg), 0);
             tc->setMiscRegNoEffect(MISCREG_SEG_ATTR(seg), dataAttr);
+            tc->setMiscRegNoEffect(MISCREG_SEG_SEL(seg), 0xB);
+            tc->setMiscRegNoEffect(MISCREG_SEG_LIMIT(seg), (uint64_t)(-1));
         }
 
         SegAttr csAttr = 0;
         csAttr.dpl = 3;
         csAttr.unusable = 0;
-        csAttr.defaultSize = 0;
+        csAttr.defaultSize = 1;
         csAttr.longMode = 1;
         csAttr.avl = 0;
         csAttr.granularity = 1;
@@ -223,6 +225,13 @@
 
         tc->setMiscRegNoEffect(MISCREG_CS_ATTR, csAttr);
 
+        tc->setMiscRegNoEffect(MISCREG_TSG_BASE, _gdtStart);
+        tc->setMiscRegNoEffect(MISCREG_TSG_EFF_BASE, _gdtStart);
+        tc->setMiscRegNoEffect(MISCREG_TSG_LIMIT, _gdtStart + _gdtSize - 1);
+
+        // Set the LDT selector to 0 to deactivate it.
+        tc->setMiscRegNoEffect(MISCREG_TSL, 0);
+
         Efer efer = 0;
         efer.sce = 1; // Enable system call extensions.
         efer.lme = 1; // Enable long mode.