From 9bacb883f111f9823277da085a65d2d1079b5a09 Mon Sep 17 00:00:00 2001
From: Spooks <62370103+Spooks4576@users.noreply.github.com>
Date: Wed, 15 Jul 2026 19:34:35 -0600
Subject: [PATCH] Fix Linux aligned mapping retention (#247)

* Fix Linux aligned mapping retention

* Cover Linux aligned mapping retention
---
 .../Memory/PhysicalVirtualMemory.cs           |  6 +-
 .../Memory/GuestMemoryAllocatorTests.cs       | 83 +++++++++++++++++++
 2 files changed, 85 insertions(+), 4 deletions(-)

diff --git a/src/SharpEmu.Core/Memory/PhysicalVirtualMemory.cs b/src/SharpEmu.Core/Memory/PhysicalVirtualMemory.cs
index f069d8f1..4e88262e 100644
--- a/src/SharpEmu.Core/Memory/PhysicalVirtualMemory.cs
+++ b/src/SharpEmu.Core/Memory/PhysicalVirtualMemory.cs
@@ -349,10 +349,8 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
         var requestedCursor = AlignUp(desiredAddress, effectiveAlignment);
         var cursor = GetAllocationSearchCursor(desiredAddress, requestedCursor, effectiveAlignment, executable);
 
-        // POSIX treats the requested address as a hint, and Rosetta may
-        // relocate whole guest windows. Over-allocate once so the returned
-        // host range always contains an aligned guest-visible start.
-        if (!OperatingSystem.IsWindows())
+        // macOS needs alignment over-allocation; Linux uses exact-address search.
+        if (OperatingSystem.IsMacOS())
         {
             var reserveSize = effectiveAlignment > PageSize
                 ? alignedSize + effectiveAlignment
diff --git a/tests/SharpEmu.Libs.Tests/Memory/GuestMemoryAllocatorTests.cs b/tests/SharpEmu.Libs.Tests/Memory/GuestMemoryAllocatorTests.cs
index 23cd11d2..435fd207 100644
--- a/tests/SharpEmu.Libs.Tests/Memory/GuestMemoryAllocatorTests.cs
+++ b/tests/SharpEmu.Libs.Tests/Memory/GuestMemoryAllocatorTests.cs
@@ -95,6 +95,32 @@ public sealed class GuestMemoryAllocatorTests
         Assert.Equal(0UL, (ulong)memory.GetPointer(address));
     }
 
+    [Fact]
+    public void AlignedAllocationDoesNotRetainOverallocatedMappingsOutsideMacOS()
+    {
+        if (OperatingSystem.IsMacOS())
+        {
+            return;
+        }
+
+        const ulong desiredAddress = 0x00005000_0000_0123;
+        const ulong alignment = 0x10000;
+        const ulong alignedAddress = 0x00005000_0001_0000;
+        const ulong allocationSize = 0x2000;
+        using var host = new RelocatingHostMemory(alignedAddress);
+        using var memory = new PhysicalVirtualMemory(host);
+
+        Assert.True(memory.TryAllocateAtOrAbove(desiredAddress, 0x1234, false, alignment, out var actualAddress));
+        Assert.Equal(alignedAddress + alignment, actualAddress);
+        Assert.Equal(
+            [
+                (alignedAddress, allocationSize),
+                (alignedAddress + alignment, allocationSize),
+            ],
+            host.AllocationCalls);
+        Assert.Equal([alignedAddress + 0x1000], host.FreedAddresses);
+    }
+
     private sealed class FakeHostMemory : IHostMemory
     {
         public ulong Allocate(ulong desiredAddress, ulong size, HostPageProtection protection) =>
@@ -197,6 +223,63 @@ public sealed class GuestMemoryAllocatorTests
         }
     }
 
+    private sealed class RelocatingHostMemory(ulong firstAddress) : IHostMemory, IDisposable
+    {
+        private bool _relocatedFirstAllocation;
+
+        public List<(ulong Address, ulong Size)> AllocationCalls { get; } = [];
+
+        public List<ulong> FreedAddresses { get; } = [];
+
+        public ulong Allocate(ulong desiredAddress, ulong size, HostPageProtection protection)
+        {
+            AllocationCalls.Add((desiredAddress, size));
+            if (!_relocatedFirstAllocation)
+            {
+                _relocatedFirstAllocation = true;
+                return firstAddress + 0x1000;
+            }
+
+            return desiredAddress;
+        }
+
+        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)
+        {
+            FreedAddresses.Add(address);
+            return 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)
+        {
+        }
+
+        public void Dispose()
+        {
+        }
+    }
+
     private sealed class LazyHostMemory(ulong address) : IHostMemory, IDisposable
     {
         public bool CommitSucceeds { get; set; } = true;