fix(memory): expand the HLE guest-allocation arena (#843)

Co-authored-by: Foued Attar <foued.attar@lyceeastier.com>

src/SharpEmu.Core/Memory/PhysicalVirtualMemory.cs

@@ -29,7 +29,13 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
     private const ulong PageSize = 0x1000;
     private const ulong HostAllocationGranularity = 0x10000;
     private const ulong GuestAllocationArenaAddress = 0x00006000_0000_0000;
-    private const ulong GuestAllocationArenaSize = 0x0100_0000;
+    // Full C++ runtimes can route large numbers of HLE-backed heap allocations
+    // through this arena. The original 16 MiB capacity could be exhausted
+    // during asset setup, turning a valid allocation request into a null
+    // pointer that failed later in unrelated guest code. Keep enough capacity
+    // for those workloads. Adapted from foufouadi's allocator-exhaustion
+    // investigation.
+    private const ulong GuestAllocationArenaSize = 0x2000_0000;
     private const ulong GuestAllocationArenaStartOffset = PageSize;
     private const ulong LargeDataReserveThreshold = 0x4000_0000UL; // 1 GiB
     private const ulong FullCommitRegionLimit = 4UL << 30;

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

@@ -14,7 +14,7 @@ public sealed class GuestMemoryAllocatorTests
     public void FreedRangesAreReusedAndCoalesced()
     {
         using var memory = new PhysicalVirtualMemory(new FakeHostMemory());
-        const ulong usableArenaSize = 0x0100_0000 - 0x1000;
+        const ulong usableArenaSize = 0x2000_0000 - 0x1000;
 
         Assert.True(memory.TryAllocateGuestMemory(0x4000, 0x1000, out var first));
         Assert.True(memory.TryAllocateGuestMemory(0x8000, 0x1000, out var second));
@@ -34,6 +34,16 @@ public sealed class GuestMemoryAllocatorTests
         Assert.Equal(first, coalesced);
     }
 
+    [Fact]
+    public void ArenaSupportsAllocationsBeyondLegacySixteenMiBLimit()
+    {
+        using var memory = new PhysicalVirtualMemory(new FakeHostMemory());
+
+        Assert.True(memory.TryAllocateGuestMemory(0x0100_0000, 0x1000, out var first));
+        Assert.True(memory.TryAllocateGuestMemory(0x0020_0000, 0x1000, out var beyondLegacyLimit));
+        Assert.Equal(first + 0x0100_0000, beyondLegacyLimit);
+    }
+
     [Fact]
     public void SegmentProtectionIsAppliedInContiguousRuns()
     {