Fix virtual memory allocation and access (#193)

* Fix virtual memory allocation and access

* Update test dependency lock file

src/SharpEmu.Core/Cpu/TrackedCpuMemory.cs

@@ -50,4 +50,9 @@ public sealed class TrackedCpuMemory : ICpuMemory, ITrackedCpuMemory, IGuestMemo
         address = 0;
         return false;
     }
+
+    public bool TryFreeGuestMemory(ulong address)
+    {
+        return _inner is IGuestMemoryAllocator allocator && allocator.TryFreeGuestMemory(address);
+    }
 }

src/SharpEmu.Core/Memory/PhysicalVirtualMemory.cs

@@ -42,7 +42,8 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
 
     private readonly IHostMemory _hostMemory;
     private ulong _guestAllocationArenaBase;
-    private ulong _guestAllocationOffset;
+    private readonly SortedDictionary<ulong, ulong> _guestAllocationFreeRanges = new();
+    private readonly Dictionary<ulong, (ulong Offset, ulong Size)> _guestAllocations = new();
     private static readonly ulong LazyReservePrimeBytes = ResolveLazyReservePrimeBytes();
 
     public PhysicalVirtualMemory(IHostMemory? hostMemory = null)
@@ -301,7 +302,9 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
                         GuestAllocationArenaSize,
                         executable: false,
                         allowAlternative: true);
-                    _guestAllocationOffset = GuestAllocationArenaStartOffset;
+                    _guestAllocationFreeRanges.Add(
+                        GuestAllocationArenaStartOffset,
+                        GuestAllocationArenaSize - GuestAllocationArenaStartOffset);
                 }
                 catch (Exception)
                 {
@@ -309,14 +312,89 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
                 }
             }
 
-            var alignedOffset = AlignUp(_guestAllocationOffset, alignment);
-            if (alignedOffset > GuestAllocationArenaSize || size > GuestAllocationArenaSize - alignedOffset)
+            ulong rangeOffset = 0;
+            ulong rangeSize = 0;
+            ulong alignedOffset = 0;
+            var found = false;
+            foreach (var range in _guestAllocationFreeRanges)
+            {
+                alignedOffset = AlignUp(range.Key, alignment);
+                if (alignedOffset >= range.Key &&
+                    alignedOffset - range.Key <= range.Value &&
+                    size <= range.Value - (alignedOffset - range.Key))
+                {
+                    rangeOffset = range.Key;
+                    rangeSize = range.Value;
+                    found = true;
+                    break;
+                }
+            }
+
+            if (!found)
             {
                 return false;
             }
 
+            _guestAllocationFreeRanges.Remove(rangeOffset);
+            if (alignedOffset > rangeOffset)
+            {
+                _guestAllocationFreeRanges.Add(rangeOffset, alignedOffset - rangeOffset);
+            }
+
+            var allocationEnd = alignedOffset + size;
+            var rangeEnd = rangeOffset + rangeSize;
+            if (allocationEnd < rangeEnd)
+            {
+                _guestAllocationFreeRanges.Add(allocationEnd, rangeEnd - allocationEnd);
+            }
+
             address = _guestAllocationArenaBase + alignedOffset;
-            _guestAllocationOffset = alignedOffset + size;
+            _guestAllocations.Add(address, (alignedOffset, size));
+            return true;
+        }
+    }
+
+    public bool TryFreeGuestMemory(ulong address)
+    {
+        lock (_guestAllocationGate)
+        {
+            if (!_guestAllocations.Remove(address, out var allocation))
+            {
+                return false;
+            }
+
+            var freeOffset = allocation.Offset;
+            var freeSize = allocation.Size;
+            ulong? previousOffset = null;
+            ulong? nextOffset = null;
+
+            foreach (var range in _guestAllocationFreeRanges)
+            {
+                if (range.Key < freeOffset)
+                {
+                    previousOffset = range.Key;
+                    continue;
+                }
+
+                nextOffset = range.Key;
+                break;
+            }
+
+            if (previousOffset is { } previous &&
+                previous + _guestAllocationFreeRanges[previous] == freeOffset)
+            {
+                freeOffset = previous;
+                freeSize += _guestAllocationFreeRanges[previous];
+                _guestAllocationFreeRanges.Remove(previous);
+            }
+
+            if (nextOffset is { } next && freeOffset + freeSize == next)
+            {
+                freeSize += _guestAllocationFreeRanges[next];
+                _guestAllocationFreeRanges.Remove(next);
+            }
+
+            _guestAllocationFreeRanges.Add(freeOffset, freeSize);
             return true;
         }
     }
@@ -380,7 +458,8 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
             }
 
             _guestAllocationArenaBase = 0;
-            _guestAllocationOffset = 0;
+            _guestAllocationFreeRanges.Clear();
+            _guestAllocations.Clear();
         }
     }
 
@@ -439,12 +518,33 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
 
     private void ApplySegmentProtection(ulong mapStart, ulong mapEnd, ProgramHeaderFlags flags)
     {
+        var runStart = mapStart;
+        var runFlags = ProgramHeaderFlags.None;
+        var hasRun = false;
+
         for (var pageAddress = mapStart; pageAddress < mapEnd; pageAddress += PageSize)
         {
             _pageProtections.TryGetValue(pageAddress, out var existingFlags);
             var mergedFlags = existingFlags | flags;
             _pageProtections[pageAddress] = mergedFlags;
-            SetProtection(pageAddress, PageSize, mergedFlags);
+
+            if (!hasRun)
+            {
+                runStart = pageAddress;
+                runFlags = mergedFlags;
+                hasRun = true;
+            }
+            else if (mergedFlags != runFlags)
+            {
+                SetProtection(runStart, pageAddress - runStart, runFlags);
+                runStart = pageAddress;
+                runFlags = mergedFlags;
+            }
+        }
+
+        if (hasRun)
+        {
+            SetProtection(runStart, mapEnd - runStart, runFlags);
         }
     }
 
@@ -789,9 +889,14 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
         _gate.EnterReadLock();
         try
         {
-            return FindRegion(virtualAddress, 1) is not null
-                ? (void*)virtualAddress
-                : null;
+            var region = FindRegion(virtualAddress, 1);
+            if (region is null ||
+                (region.IsReservedOnly && !EnsureRangeCommitted(virtualAddress, 1, region)))
+            {
+                return null;
+            }
+
+            return (void*)virtualAddress;
         }
         finally
         {

src/SharpEmu.Core/Memory/VirtualMemory.cs

@@ -41,15 +41,14 @@ public sealed class VirtualMemory : IVirtualMemory
 
         lock (_gate)
         {
-            foreach (var existing in _regions)
+            var insertionIndex = FindInsertionIndex(virtualAddress);
+            if ((insertionIndex > 0 && virtualAddress < _regions[insertionIndex - 1].EndAddress) ||
+                (insertionIndex < _regions.Count && endAddress > _regions[insertionIndex].Region.VirtualAddress))
             {
-                if (virtualAddress < existing.EndAddress && endAddress > existing.Region.VirtualAddress)
-                {
-                    throw new InvalidOperationException("Attempted to map an overlapping virtual memory region.");
-                }
+                throw new InvalidOperationException("Attempted to map an overlapping virtual memory region.");
             }
 
-            _regions.Add(new MappedRegion(
+            _regions.Insert(insertionIndex, new MappedRegion(
                 new VirtualMemoryRegion(virtualAddress, memorySize, fileOffset, (ulong)fileData.Length, protection),
                 endAddress,
                 backingMemory));
@@ -74,12 +73,12 @@ public sealed class VirtualMemory : IVirtualMemory
     {
         lock (_gate)
         {
-            if (!TryResolveRegion(virtualAddress, destination.Length, out var region, out var offset))
+            if (!TryValidateRange(virtualAddress, destination.Length, ProgramHeaderFlags.Read, out var regionIndex))
             {
                 return false;
             }
 
-            region.BackingMemory.AsSpan(offset, destination.Length).CopyTo(destination);
+            CopyFromRegions(virtualAddress, destination, regionIndex);
             return true;
         }
     }
@@ -88,39 +87,127 @@ public sealed class VirtualMemory : IVirtualMemory
     {
         lock (_gate)
         {
-            if (!TryResolveRegion(virtualAddress, source.Length, out var region, out var offset))
+            if (!TryValidateRange(virtualAddress, source.Length, ProgramHeaderFlags.Write, out var regionIndex))
             {
                 return false;
             }
 
-            source.CopyTo(region.BackingMemory.AsSpan(offset, source.Length));
+            CopyToRegions(virtualAddress, source, regionIndex);
             return true;
         }
     }
 
-    private bool TryResolveRegion(ulong virtualAddress, int length, out MappedRegion region, out int offset)
+    private bool TryValidateRange(
+        ulong virtualAddress,
+        int length,
+        ProgramHeaderFlags requiredProtection,
+        out int regionIndex)
     {
-        foreach (var candidate in _regions)
+        regionIndex = FindContainingRegionIndex(virtualAddress);
+        if (regionIndex < 0)
         {
-            if (virtualAddress < candidate.Region.VirtualAddress || virtualAddress >= candidate.EndAddress)
-            {
-                continue;
-            }
-
-            var candidateOffset = checked((int)(virtualAddress - candidate.Region.VirtualAddress));
-            if (candidateOffset + length > candidate.BackingMemory.Length)
-            {
-                break;
-            }
-
-            region = candidate;
-            offset = candidateOffset;
-            return true;
+            return false;
         }
 
-        region = default;
-        offset = 0;
-        return false;
+        var currentAddress = virtualAddress;
+        var remaining = length;
+        var currentIndex = regionIndex;
+        while (true)
+        {
+            if (currentIndex >= _regions.Count)
+            {
+                return false;
+            }
+
+            var region = _regions[currentIndex];
+            if (currentAddress < region.Region.VirtualAddress ||
+                currentAddress >= region.EndAddress ||
+                (region.Region.Protection & requiredProtection) == 0)
+            {
+                return false;
+            }
+
+            if (remaining == 0)
+            {
+                return true;
+            }
+
+            var available = region.EndAddress - currentAddress;
+            var chunkLength = (int)Math.Min((ulong)remaining, available);
+            remaining -= chunkLength;
+            if (remaining == 0)
+            {
+                return true;
+            }
+
+            currentAddress += (ulong)chunkLength;
+            currentIndex++;
+        }
+    }
+
+    private int FindContainingRegionIndex(ulong virtualAddress)
+    {
+        var insertionIndex = FindInsertionIndex(virtualAddress);
+        if (insertionIndex < _regions.Count &&
+            _regions[insertionIndex].Region.VirtualAddress == virtualAddress)
+        {
+            return insertionIndex;
+        }
+
+        var candidateIndex = insertionIndex - 1;
+        return candidateIndex >= 0 && virtualAddress < _regions[candidateIndex].EndAddress
+            ? candidateIndex
+            : -1;
+    }
+
+    private void CopyFromRegions(ulong virtualAddress, Span<byte> destination, int regionIndex)
+    {
+        var copied = 0;
+        var currentAddress = virtualAddress;
+        while (copied < destination.Length)
+        {
+            var region = _regions[regionIndex++];
+            var regionOffset = checked((int)(currentAddress - region.Region.VirtualAddress));
+            var chunkLength = Math.Min(destination.Length - copied, region.BackingMemory.Length - regionOffset);
+            region.BackingMemory.AsSpan(regionOffset, chunkLength).CopyTo(destination[copied..]);
+            copied += chunkLength;
+            currentAddress += (ulong)chunkLength;
+        }
+    }
+
+    private void CopyToRegions(ulong virtualAddress, ReadOnlySpan<byte> source, int regionIndex)
+    {
+        var copied = 0;
+        var currentAddress = virtualAddress;
+        while (copied < source.Length)
+        {
+            var region = _regions[regionIndex++];
+            var regionOffset = checked((int)(currentAddress - region.Region.VirtualAddress));
+            var chunkLength = Math.Min(source.Length - copied, region.BackingMemory.Length - regionOffset);
+            source.Slice(copied, chunkLength).CopyTo(region.BackingMemory.AsSpan(regionOffset, chunkLength));
+            copied += chunkLength;
+            currentAddress += (ulong)chunkLength;
+        }
+    }
+
+    private int FindInsertionIndex(ulong virtualAddress)
+    {
+        var lower = 0;
+        var upper = _regions.Count;
+        while (lower < upper)
+        {
+            var middle = lower + ((upper - lower) / 2);
+            if (_regions[middle].Region.VirtualAddress < virtualAddress)
+            {
+                lower = middle + 1;
+            }
+            else
+            {
+                upper = middle;
+            }
+        }
+
+        return lower;
     }
 
     private readonly record struct MappedRegion(VirtualMemoryRegion Region, ulong EndAddress, byte[] BackingMemory);

src/SharpEmu.HLE/IGuestMemoryAllocator.cs

@@ -6,4 +6,6 @@ namespace SharpEmu.HLE;
 public interface IGuestMemoryAllocator
 {
     bool TryAllocateGuestMemory(ulong size, ulong alignment, out ulong address);
+
+    bool TryFreeGuestMemory(ulong address);
 }

src/SharpEmu.Libs/Kernel/KernelPthreadCompatExports.cs

@@ -629,6 +629,7 @@ public static class KernelPthreadCompatExports
         }
         if (!InitializeMutexObject(ctx, handle, state))
         {
+            TryFreeOpaqueObject(ctx, handle);
             state.Semaphore.Dispose();
             return (int)OrbisGen2Result.ORBIS_GEN2_ERROR_MEMORY_FAULT;
         }
@@ -641,6 +642,7 @@ public static class KernelPthreadCompatExports
             _mutexStates.TryRemove(mutexAddress, out _);
             _mutexStates.TryRemove(handle, out _);
 
+            TryFreeOpaqueObject(ctx, handle);
             state.Semaphore.Dispose();
             return (int)OrbisGen2Result.ORBIS_GEN2_ERROR_MEMORY_FAULT;
         }
@@ -668,6 +670,7 @@ public static class KernelPthreadCompatExports
         }
 
         _ = KernelMemoryCompatExports.TryWriteUInt64Compat(ctx, mutexAddress, 0);
+        TryFreeOpaqueObject(ctx, resolvedAddress);
         state.Semaphore.Dispose();
         return (int)OrbisGen2Result.ORBIS_GEN2_OK;
     }
@@ -895,6 +898,7 @@ public static class KernelPthreadCompatExports
         var initialState = new PthreadMutexAttrState(MutexTypeErrorCheck, 0);
         if (!WriteMutexAttrObject(ctx, handle, initialState))
         {
+            TryFreeOpaqueObject(ctx, handle);
             return (int)OrbisGen2Result.ORBIS_GEN2_ERROR_MEMORY_FAULT;
         }
 
@@ -912,6 +916,7 @@ public static class KernelPthreadCompatExports
                 _mutexAttrStates.Remove(handle);
             }
 
+            TryFreeOpaqueObject(ctx, handle);
             return (int)OrbisGen2Result.ORBIS_GEN2_ERROR_MEMORY_FAULT;
         }
 
@@ -935,6 +940,7 @@ public static class KernelPthreadCompatExports
             }
         }
 
+        TryFreeOpaqueObject(ctx, resolvedAddress);
         return (int)OrbisGen2Result.ORBIS_GEN2_OK;
     }
 
@@ -1195,6 +1201,7 @@ public static class KernelPthreadCompatExports
         {
             if (_condStates.TryGetValue(condAddress, out var raced))
             {
+                TryFreeOpaqueObject(ctx, handle);
                 resolvedAddress = condAddress;
                 state = raced;
                 return true;
@@ -1212,6 +1219,7 @@ public static class KernelPthreadCompatExports
                 _condStates.Remove(handle);
             }
 
+            TryFreeOpaqueObject(ctx, handle);
             return false;
         }
 
@@ -1231,7 +1239,22 @@ public static class KernelPthreadCompatExports
 
         Span<byte> initialData = stackalloc byte[size];
         initialData.Clear();
-        return ctx.Memory.TryWrite(address, initialData);
+        if (ctx.Memory.TryWrite(address, initialData))
+        {
+            return true;
+        }
+
+        allocator.TryFreeGuestMemory(address);
+        address = 0;
+        return false;
+    }
+
+    private static void TryFreeOpaqueObject(CpuContext ctx, ulong address)
+    {
+        if (ctx.Memory is IGuestMemoryAllocator allocator)
+        {
+            allocator.TryFreeGuestMemory(address);
+        }
     }
 
     private static bool InitializeMutexObject(CpuContext ctx, ulong address, PthreadMutexState state) =>
@@ -1269,6 +1292,7 @@ public static class KernelPthreadCompatExports
                 _condStates.Remove(handle);
             }
 
+            TryFreeOpaqueObject(ctx, handle);
             return (int)OrbisGen2Result.ORBIS_GEN2_ERROR_MEMORY_FAULT;
         }
 
@@ -1293,6 +1317,7 @@ public static class KernelPthreadCompatExports
         }
 
         _ = KernelMemoryCompatExports.TryWriteUInt64Compat(ctx, condAddress, 0);
+        TryFreeOpaqueObject(ctx, resolvedAddress);
         return (int)OrbisGen2Result.ORBIS_GEN2_OK;
     }
 
@@ -1775,6 +1800,7 @@ public static class KernelPthreadCompatExports
         }
         if (!InitializeMutexObject(ctx, handle, createdState))
         {
+            TryFreeOpaqueObject(ctx, handle);
             resolvedAddress = 0;
             state = null;
             return false;
@@ -1784,12 +1810,14 @@ public static class KernelPthreadCompatExports
         {
             if (_mutexStates.TryGetValue(mutexAddress, out state))
             {
+                TryFreeOpaqueObject(ctx, handle);
                 resolvedAddress = mutexAddress;
                 return true;
             }
 
             if (_mutexStates.TryGetValue(handle, out state))
             {
+                TryFreeOpaqueObject(ctx, handle);
                 resolvedAddress = handle;
                 return true;
             }
@@ -1803,6 +1831,7 @@ public static class KernelPthreadCompatExports
             _mutexStates.TryRemove(mutexAddress, out _);
             _mutexStates.TryRemove(handle, out _);
 
+            TryFreeOpaqueObject(ctx, handle);
             resolvedAddress = 0;
             state = null;
             return false;

tests/SharpEmu.Libs.Tests/Memory/GuestMemoryAllocatorTests.cs

@@ -0,0 +1,254 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.Core.Memory;
+using SharpEmu.Core.Loader;
+using SharpEmu.HLE.Host;
+using Xunit;
+
+namespace SharpEmu.Libs.Tests.Memory;
+
+public sealed class GuestMemoryAllocatorTests
+{
+    [Fact]
+    public void FreedRangesAreReusedAndCoalesced()
+    {
+        using var memory = new PhysicalVirtualMemory(new FakeHostMemory());
+        const ulong usableArenaSize = 0x0100_0000 - 0x1000;
+
+        Assert.True(memory.TryAllocateGuestMemory(0x4000, 0x1000, out var first));
+        Assert.True(memory.TryAllocateGuestMemory(0x8000, 0x1000, out var second));
+        Assert.True(memory.TryAllocateGuestMemory(usableArenaSize - 0xC000, 0x1000, out var third));
+        Assert.False(memory.TryAllocateGuestMemory(1, 1, out _));
+
+        Assert.True(memory.TryFreeGuestMemory(second));
+        Assert.True(memory.TryAllocateGuestMemory(0x8000, 0x1000, out var reused));
+        Assert.Equal(second, reused);
+
+        Assert.True(memory.TryFreeGuestMemory(first));
+        Assert.True(memory.TryFreeGuestMemory(reused));
+        Assert.True(memory.TryFreeGuestMemory(third));
+        Assert.False(memory.TryFreeGuestMemory(third));
+
+        Assert.True(memory.TryAllocateGuestMemory(usableArenaSize, 0x1000, out var coalesced));
+        Assert.Equal(first, coalesced);
+    }
+
+    [Fact]
+    public void SegmentProtectionIsAppliedInContiguousRuns()
+    {
+        const ulong pageSize = 0x1000;
+        using var host = new RecordingHostMemory(3 * pageSize);
+        using var memory = new PhysicalVirtualMemory(host);
+
+        memory.Map(host.Address, 3 * pageSize, 0, ReadOnlySpan<byte>.Empty, ProgramHeaderFlags.Read);
+
+        Assert.Equal(
+            [
+                (host.Address, 3 * pageSize, HostPageProtection.ReadWrite),
+                (host.Address, 3 * pageSize, HostPageProtection.ReadOnly),
+            ],
+            host.ProtectionCalls);
+
+        host.ProtectionCalls.Clear();
+        memory.Map(host.Address + pageSize, pageSize, 0, ReadOnlySpan<byte>.Empty, ProgramHeaderFlags.Write);
+        host.ProtectionCalls.Clear();
+
+        memory.Map(host.Address, 3 * pageSize, 0, ReadOnlySpan<byte>.Empty, ProgramHeaderFlags.Execute);
+
+        Assert.Equal(
+            [
+                (host.Address, 3 * pageSize, HostPageProtection.ReadWriteExecute),
+                (host.Address, pageSize, HostPageProtection.ReadExecute),
+                (host.Address + pageSize, pageSize, HostPageProtection.ReadWriteExecute),
+                (host.Address + (2 * pageSize), pageSize, HostPageProtection.ReadExecute),
+            ],
+            host.ProtectionCalls);
+    }
+
+    [Fact]
+    public unsafe void GetPointerCommitsLazyPageBeforeReturningIt()
+    {
+        const ulong address = 0x00005000_0000_0000;
+        const ulong pageSize = 0x1000;
+        using var host = new LazyHostMemory(address);
+        using var memory = new PhysicalVirtualMemory(host);
+        memory.AllocateAt(address, (4UL << 30) + pageSize, executable: false, allowAlternative: false);
+        host.CommitCalls.Clear();
+
+        var pointer = memory.GetPointer(address + 0x123);
+
+        Assert.Equal(address + 0x123, (ulong)pointer);
+        Assert.Equal([(address, pageSize, HostPageProtection.ReadWrite)], host.CommitCalls);
+    }
+
+    [Fact]
+    public unsafe void GetPointerReturnsNullWhenLazyCommitFails()
+    {
+        const ulong address = 0x00005000_0000_0000;
+        using var host = new LazyHostMemory(address);
+        using var memory = new PhysicalVirtualMemory(host);
+        memory.AllocateAt(address, (4UL << 30) + 0x1000, executable: false, allowAlternative: false);
+        host.CommitCalls.Clear();
+        host.CommitSucceeds = false;
+
+        Assert.Equal(0UL, (ulong)memory.GetPointer(address));
+    }
+
+    private sealed class FakeHostMemory : IHostMemory
+    {
+        public ulong Allocate(ulong desiredAddress, ulong size, HostPageProtection protection) =>
+            desiredAddress != 0 ? desiredAddress : 0x00007000_0000_0000;
+
+        public ulong Reserve(ulong desiredAddress, ulong size, HostPageProtection protection) =>
+            Allocate(desiredAddress, size, protection);
+
+        public bool Commit(ulong address, ulong size, HostPageProtection protection) => true;
+
+        public bool Free(ulong address) => true;
+
+        public bool Protect(ulong address, ulong size, HostPageProtection protection, out uint rawOldProtection)
+        {
+            rawOldProtection = 0;
+            return true;
+        }
+
+        public bool ProtectRaw(ulong address, ulong size, uint rawProtection, out uint rawOldProtection)
+        {
+            rawOldProtection = 0;
+            return true;
+        }
+
+        public bool Query(ulong address, out HostRegionInfo info)
+        {
+            info = default;
+            return false;
+        }
+
+        public void FlushInstructionCache(ulong address, ulong size)
+        {
+        }
+    }
+
+    private sealed class RecordingHostMemory : IHostMemory, IDisposable
+    {
+        private readonly nint _allocation;
+        private bool _freed;
+
+        public RecordingHostMemory(ulong size)
+        {
+            _allocation = System.Runtime.InteropServices.Marshal.AllocHGlobal(checked((nint)(size + 0xFFF)));
+            Address = (unchecked((ulong)_allocation) + 0xFFF) & ~0xFFFUL;
+        }
+
+        public ulong Address { get; }
+
+        public List<(ulong Address, ulong Size, HostPageProtection Protection)> ProtectionCalls { get; } = [];
+
+        public ulong Allocate(ulong desiredAddress, ulong size, HostPageProtection protection) =>
+            desiredAddress == Address ? Address : 0;
+
+        public ulong Reserve(ulong desiredAddress, ulong size, HostPageProtection protection) => 0;
+
+        public bool Commit(ulong address, ulong size, HostPageProtection protection) => true;
+
+        public bool Free(ulong address)
+        {
+            if (address != Address || _freed)
+            {
+                return false;
+            }
+
+            System.Runtime.InteropServices.Marshal.FreeHGlobal(_allocation);
+            _freed = true;
+            return true;
+        }
+
+        public bool Protect(ulong address, ulong size, HostPageProtection protection, out uint rawOldProtection)
+        {
+            ProtectionCalls.Add((address, size, protection));
+            rawOldProtection = 0;
+            return true;
+        }
+
+        public bool ProtectRaw(ulong address, ulong size, uint rawProtection, out uint rawOldProtection)
+        {
+            rawOldProtection = 0;
+            return true;
+        }
+
+        public bool Query(ulong address, out HostRegionInfo info)
+        {
+            info = default;
+            return false;
+        }
+
+        public void FlushInstructionCache(ulong address, ulong size)
+        {
+        }
+
+        public void Dispose()
+        {
+            if (!_freed)
+            {
+                System.Runtime.InteropServices.Marshal.FreeHGlobal(_allocation);
+                _freed = true;
+            }
+        }
+    }
+
+    private sealed class LazyHostMemory(ulong address) : IHostMemory, IDisposable
+    {
+        public bool CommitSucceeds { get; set; } = true;
+
+        public List<(ulong Address, ulong Size, HostPageProtection Protection)> CommitCalls { get; } = [];
+
+        public ulong Allocate(ulong desiredAddress, ulong size, HostPageProtection protection) => 0;
+
+        public ulong Reserve(ulong desiredAddress, ulong size, HostPageProtection protection) =>
+            desiredAddress == address ? address : 0;
+
+        public bool Commit(ulong commitAddress, ulong size, HostPageProtection protection)
+        {
+            CommitCalls.Add((commitAddress, size, protection));
+            return CommitSucceeds;
+        }
+
+        public bool Free(ulong freeAddress) => freeAddress == address;
+
+        public bool Protect(ulong protectAddress, ulong size, HostPageProtection protection, out uint rawOldProtection)
+        {
+            rawOldProtection = 0;
+            return true;
+        }
+
+        public bool ProtectRaw(ulong protectAddress, ulong size, uint rawProtection, out uint rawOldProtection)
+        {
+            rawOldProtection = 0;
+            return true;
+        }
+
+        public bool Query(ulong queryAddress, out HostRegionInfo info)
+        {
+            var pageAddress = queryAddress & ~0xFFFUL;
+            info = new HostRegionInfo(
+                pageAddress,
+                address,
+                0x1000,
+                HostRegionState.Reserved,
+                0,
+                HostPageProtection.NoAccess,
+                0,
+                0);
+            return true;
+        }
+
+        public void FlushInstructionCache(ulong flushAddress, ulong size)
+        {
+        }
+
+        public void Dispose()
+        {
+        }
+    }
+}

tests/SharpEmu.Libs.Tests/Memory/VirtualMemoryTests.cs

@@ -0,0 +1,87 @@
+// Copyright (C) 2026 SharpEmu Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+using SharpEmu.Core.Loader;
+using SharpEmu.Core.Memory;
+using Xunit;
+
+namespace SharpEmu.Libs.Tests.Memory;
+
+public sealed class VirtualMemoryTests
+{
+    [Fact]
+    public void OutOfOrderMappingsRemainSortedAndResolveAtBoundaries()
+    {
+        var memory = new VirtualMemory();
+        memory.Map(0x3000, 0x100, 0, [3], ProgramHeaderFlags.Read | ProgramHeaderFlags.Write);
+        memory.Map(0x1000, 0x100, 0, [1], ProgramHeaderFlags.Read | ProgramHeaderFlags.Write);
+        memory.Map(0x2000, 0x100, 0, [2], ProgramHeaderFlags.Read | ProgramHeaderFlags.Write);
+
+        Assert.Equal([0x1000UL, 0x2000UL, 0x3000UL], memory.SnapshotRegions().Select(region => region.VirtualAddress));
+
+        Span<byte> value = stackalloc byte[1];
+        Assert.True(memory.TryRead(0x1000, value));
+        Assert.Equal(1, value[0]);
+        Assert.True(memory.TryRead(0x2000, value));
+        Assert.Equal(2, value[0]);
+        Assert.True(memory.TryRead(0x3000, value));
+        Assert.Equal(3, value[0]);
+        Assert.False(memory.TryRead(0x1100, value));
+        Assert.False(memory.TryRead(0x0FFF, value));
+    }
+
+    [Fact]
+    public void MappingRejectsOverlapWithEitherNeighbor()
+    {
+        var memory = new VirtualMemory();
+        memory.Map(0x2000, 0x100, 0, [], ProgramHeaderFlags.Read);
+        memory.Map(0x4000, 0x100, 0, [], ProgramHeaderFlags.Read);
+
+        Assert.Throws<InvalidOperationException>(() =>
+            memory.Map(0x1FFF, 2, 0, [], ProgramHeaderFlags.Read));
+        Assert.Throws<InvalidOperationException>(() =>
+            memory.Map(0x3FFF, 2, 0, [], ProgramHeaderFlags.Read));
+
+        memory.Map(0x2100, 0x1F00, 0, [], ProgramHeaderFlags.Read);
+        Assert.Equal(3, memory.SnapshotRegions().Count);
+    }
+
+    [Fact]
+    public void ReadAndWriteSpanAdjacentRegions()
+    {
+        var memory = new VirtualMemory();
+        const ProgramHeaderFlags protection = ProgramHeaderFlags.Read | ProgramHeaderFlags.Write;
+        memory.Map(0x1000, 4, 0, [1, 2, 3, 4], protection);
+        memory.Map(0x1004, 4, 0, [5, 6, 7, 8], protection);
+
+        Span<byte> read = stackalloc byte[4];
+        Assert.True(memory.TryRead(0x1002, read));
+        Assert.Equal([3, 4, 5, 6], read.ToArray());
+
+        Assert.True(memory.TryWrite(0x1002, [9, 10, 11, 12]));
+        Assert.True(memory.TryRead(0x1000, read));
+        Assert.Equal([1, 2, 9, 10], read.ToArray());
+        Assert.True(memory.TryRead(0x1004, read));
+        Assert.Equal([11, 12, 7, 8], read.ToArray());
+    }
+
+    [Fact]
+    public void AccessRequiresPermissionAcrossEntireRange()
+    {
+        var memory = new VirtualMemory();
+        memory.Map(0x1000, 4, 0, [1, 2, 3, 4], ProgramHeaderFlags.Read | ProgramHeaderFlags.Write);
+        memory.Map(0x1004, 4, 0, [5, 6, 7, 8], ProgramHeaderFlags.Read);
+        memory.Map(0x2000, 4, 0, [1, 2, 3, 4], ProgramHeaderFlags.Execute);
+        memory.Map(0x3000, 4, 0, [], ProgramHeaderFlags.Write);
+
+        Assert.False(memory.TryWrite(0x1002, [9, 9, 9, 9]));
+        Span<byte> unchanged = stackalloc byte[4];
+        Assert.True(memory.TryRead(0x1000, unchanged));
+        Assert.Equal([1, 2, 3, 4], unchanged.ToArray());
+
+        Assert.False(memory.TryRead(0x2000, unchanged));
+        Assert.False(memory.TryWrite(0x2000, [9]));
+        Assert.False(memory.TryRead(0x3000, unchanged));
+        Assert.True(memory.TryWrite(0x3000, [9]));
+    }
+}

tests/SharpEmu.Libs.Tests/SharpEmu.Libs.Tests.csproj

@@ -7,9 +7,11 @@ SPDX-License-Identifier: GPL-2.0-or-later
   <PropertyGroup>
     <IsPackable>false</IsPackable>
     <GenerateDocumentationFile>false</GenerateDocumentationFile>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 
   <ItemGroup>
+    <ProjectReference Include="..\..\src\SharpEmu.Core\SharpEmu.Core.csproj" />
     <ProjectReference Include="..\..\src\SharpEmu.Libs\SharpEmu.Libs.csproj" />
     <ProjectReference Include="..\..\src\SharpEmu.HLE\SharpEmu.HLE.csproj" />
   </ItemGroup>

tests/SharpEmu.Libs.Tests/packages.lock.json

@@ -149,6 +149,15 @@
           "xunit.extensibility.core": "[2.9.3]"
         }
       },
+      "sharpemu.core": {
+        "type": "Project",
+        "dependencies": {
+          "Iced": "[1.21.0, )",
+          "SharpEmu.HLE": "[1.0.0, )",
+          "SharpEmu.Libs": "[1.0.0, )",
+          "SharpEmu.Logging": "[1.0.0, )"
+        }
+      },
       "sharpemu.hle": {
         "type": "Project",
         "dependencies": {
@@ -168,6 +177,12 @@
       "sharpemu.logging": {
         "type": "Project"
       },
+      "Iced": {
+        "type": "CentralTransitive",
+        "requested": "[1.21.0, )",
+        "resolved": "1.21.0",
+        "contentHash": "dv5+81Q1TBQvVMSOOOmRcjJmvWcX3BZPZsIq31+RLc5cNft0IHAyNlkdb7ZarOWG913PyBoFDsDXoCIlKmLclg=="
+      },
       "Silk.NET.Vulkan": {
         "type": "CentralTransitive",
         "requested": "[2.23.0, )",