UserspaceEmulator: Add proper segment registers

Some things will flow better if we're able to index into a table of our
segment registers.

DevTools/UserspaceEmulator/SoftCPU.cpp

@@ -36,6 +36,11 @@ SoftCPU::SoftCPU(Emulator& emulator)
     : m_emulator(emulator)
 {
     memset(m_gpr, 0, sizeof(m_gpr));
+
+    m_segment[(int)X86::SegmentRegister::CS] = 0x18;
+    m_segment[(int)X86::SegmentRegister::DS] = 0x20;
+    m_segment[(int)X86::SegmentRegister::ES] = 0x20;
+    m_segment[(int)X86::SegmentRegister::SS] = 0x20;
 }
 
 void SoftCPU::dump() const

DevTools/UserspaceEmulator/SoftCPU.h

@@ -56,6 +56,9 @@ public:
     void push32(u32);
     u32 pop32();
 
+    u16 segment(X86::SegmentRegister seg) const { return m_segment[(int)seg]; }
+    u16& segment(X86::SegmentRegister seg) { return m_segment[(int)seg]; }
+
     u32 gpr32(X86::RegisterIndex32 reg) const { return m_gpr[reg].full_u32; }
     u32& gpr32(X86::RegisterIndex32 reg) { return m_gpr[reg].full_u32; }
 
@@ -109,10 +112,10 @@ public:
     void set_pf(bool value) { m_pf = value; }
     void set_cf(bool value) { m_cf = value; }
 
-    u16 cs() const { return 0x18; }
-    u16 ds() const { return 0x20; }
-    u16 es() const { return 0x20; }
-    u16 ss() const { return 0x20; }
+    u16 cs() const { return m_segment[(int)X86::SegmentRegister::CS]; }
+    u16 ds() const { return m_segment[(int)X86::SegmentRegister::DS]; }
+    u16 es() const { return m_segment[(int)X86::SegmentRegister::ES]; }
+    u16 ss() const { return m_segment[(int)X86::SegmentRegister::SS]; }
 
     u32 read_memory32(X86::LogicalAddress);
     void write_memory32(X86::LogicalAddress, u32);
@@ -592,6 +595,7 @@ private:
     Emulator& m_emulator;
 
     PartAddressableRegister m_gpr[8];
+    u16 m_segment[8] { 0 };
 
     bool m_of { false };
     bool m_sf { false };