core: page-aware TryReadUtf8Z and unify exit/_exit handling (#57)

Read guest C strings in page-bounded chunks without heap allocations.
Return false when the buffer fills without a null terminator. Route exit
and _exit through RequestProcessExit.

src/SharpEmu.GUI/MainWindow.axaml

@@ -43,7 +43,8 @@ SPDX-License-Identifier: GPL-2.0-or-later
     <!-- Title bar -->
     <Grid x:Name="TitleBar" Grid.Row="0" Background="{StaticResource ChromeBrush}">
       <StackPanel Orientation="Horizontal" Spacing="10" Margin="16,0" VerticalAlignment="Center">
-        <Image Source="avares://SharpEmu.GUI/Assets/logo.png" Width="20" Height="20" />
+        <Image Source="avares://SharpEmu.GUI/Assets/SharpEmu.ico" Width="20" Height="20"
+               RenderOptions.BitmapInterpolationMode="HighQuality" />
         <TextBlock Text="SharpEmu" FontSize="14" FontWeight="SemiBold" VerticalAlignment="Center" />
         <Border Classes="pill">
           <TextBlock x:Name="VersionText" Text="v0.0.1" FontSize="11" Foreground="{StaticResource MutedBrush}" />

src/SharpEmu.GUI/SharpEmu.GUI.csproj

@@ -21,7 +21,6 @@ SPDX-License-Identifier: GPL-2.0-or-later
   </ItemGroup>
 
   <ItemGroup>
-    <AvaloniaResource Include="..\..\assets\images\logo.png" Link="Assets/logo.png" />
     <AvaloniaResource Include="..\..\assets\images\SharpEmu.ico" Link="Assets/SharpEmu.ico" />
   </ItemGroup>
 

src/SharpEmu.Libs/Kernel/KernelExports.cs

@@ -52,14 +52,7 @@ public static class KernelExports
         ExportName = "exit",
         Target = Generation.Gen4 | Generation.Gen5,
         LibraryName = "libKernel")]
-    public static int Exit(CpuContext ctx)
+    public static int Exit(CpuContext ctx) => RequestProcessExit(ctx, "exit");
-    {
-        var status = unchecked((int)ctx[CpuRegister.Rdi]);
-        Console.Error.WriteLine($"[LOADER][INFO] exit(status={status})");
-        GuestThreadExecution.RequestCurrentEntryExit("exit", status);
-        ctx[CpuRegister.Rax] = unchecked((ulong)status);
-        return (int)OrbisGen2Result.ORBIS_GEN2_OK;
-    }
 
     [SysAbiExport(
         Nid = "XKRegsFpEpk",
@@ -172,11 +165,7 @@ public static class KernelExports
         ExportName = "_exit",
         Target = Generation.Gen4 | Generation.Gen5,
         LibraryName = "libKernel")]
-    public static int UnderscoreExit(CpuContext ctx)
+    public static int UnderscoreExit(CpuContext ctx) => RequestProcessExit(ctx, "_exit");
-    {
-        _ = ctx;
-        return (int)OrbisGen2Result.ORBIS_GEN2_OK;
-    }
 
     [SysAbiExport(
         Nid = "Ac86z8q7T8A",
@@ -437,4 +426,13 @@ public static class KernelExports
     {
         return string.Equals(Environment.GetEnvironmentVariable("SHARPEMU_LOG_PTHREADS"), "1", StringComparison.Ordinal);
     }
+
+    private static int RequestProcessExit(CpuContext ctx, string syscallName)
+    {
+        var status = unchecked((int)ctx[CpuRegister.Rdi]);
+        Console.Error.WriteLine($"[LOADER][INFO] {syscallName}(status={status})");
+        GuestThreadExecution.RequestCurrentEntryExit(syscallName, status);
+        ctx[CpuRegister.Rax] = unchecked((ulong)status);
+        return (int)OrbisGen2Result.ORBIS_GEN2_OK;
+    }
 }

src/SharpEmu.Libs/Kernel/KernelRuntimeCompatExports.cs

@@ -1469,26 +1469,42 @@ public static class KernelRuntimeCompatExports
             return false;
         }
 
-        var bytes = new List<byte>(Math.Min(maxLength, 64));
+        const int pageSize = 4096;
-        Span<byte> one = stackalloc byte[1];
+        const int inlineChunkSize = 64;
-        for (var i = 0; i < maxLength; i++)
+        Span<byte> buffer = stackalloc byte[Math.Min(maxLength, 512)];
+        var length = 0;
+
+        for (var offset = 0; offset < maxLength && length < buffer.Length;)
         {
-            if (!ctx.Memory.TryRead(address + (ulong)i, one))
+            var current = address + (ulong)offset;
+            var pageRemaining = pageSize - (int)(current & (pageSize - 1));
+            var chunkSize = Math.Min(
+                buffer.Length - length,
+                Math.Min(maxLength - offset, Math.Min(inlineChunkSize, pageRemaining)));
+
+            if (chunkSize <= 0)
             {
                 return false;
             }
 
-            if (one[0] == 0)
+            var chunk = buffer.Slice(length, chunkSize);
+            if (!ctx.Memory.TryRead(current, chunk))
             {
-                value = Encoding.UTF8.GetString(bytes.ToArray());
+                return false;
+            }
+
+            var nulIndex = chunk.IndexOf((byte)0);
+            if (nulIndex >= 0)
+            {
+                value = Encoding.UTF8.GetString(buffer[..(length + nulIndex)]);
                 return true;
             }
 
-            bytes.Add(one[0]);
+            length += chunkSize;
+            offset += chunkSize;
         }
 
-        value = Encoding.UTF8.GetString(bytes.ToArray());
+        return false;
-        return true;
     }
 
     private static ulong GetTlsScratchAddress(CpuContext ctx, ulong offset)