[Kernel] Return largest available direct-memory span (#334)

src/SharpEmu.Libs/Kernel/KernelMemoryCompatExports.cs

@@ -2459,7 +2459,20 @@ public static partial class KernelMemoryCompatExports
                 return (int)OrbisGen2Result.ORBIS_GEN2_ERROR_INVALID_ARGUMENT;
             }
 
-            if (!TryFindAvailableDirectMemorySpanLocked(searchStart, searchEnd, alignment, out var candidate, out var rangeAvailable))
+            bool foundSpan;
+            ulong candidate;
+            ulong rangeAvailable;
+            lock (_memoryGate)
+            {
+                foundSpan = TryFindAvailableDirectMemorySpanLocked(
+                    searchStart,
+                    searchEnd,
+                    alignment,
+                    out candidate,
+                    out rangeAvailable);
+            }
+
+            if (!foundSpan)
             {
                 return (int)OrbisGen2Result.ORBIS_GEN2_ERROR_NOT_FOUND;
             }
@@ -5909,9 +5922,12 @@ public static partial class KernelMemoryCompatExports
             var gapEnd = Math.Min(allocation.Start, effectiveEnd);
             if (candidate < gapEnd)
             {
-                spanStart = candidate;
+                var candidateLength = gapEnd - candidate;
-                spanLength = gapEnd - candidate;
+                if (candidateLength > spanLength)
-                return true;
+                {
+                    spanStart = candidate;
+                    spanLength = candidateLength;
+                }
             }
 
             if (allocation.Start >= effectiveEnd)
@@ -5922,12 +5938,20 @@ public static partial class KernelMemoryCompatExports
             candidate = AlignUp(Math.Max(candidate, allocationEnd), alignment);
             if (candidate >= effectiveEnd)
             {
-                return false;
+                break;
+            }
+        }
+
+        if (candidate < effectiveEnd)
+        {
+            var candidateLength = effectiveEnd - candidate;
+            if (candidateLength > spanLength)
+            {
+                spanStart = candidate;
+                spanLength = candidateLength;
             }
         }
 
-        spanStart = candidate;
-        spanLength = effectiveEnd - candidate;
         return spanLength != 0;
     }
 

tests/SharpEmu.Libs.Tests/Kernel/KernelMemoryCompatExportsTests.cs

@@ -9,8 +9,20 @@ using Xunit;
 
 namespace SharpEmu.Libs.Tests.Kernel;
 
+[CollectionDefinition(KernelMemoryCompatStateCollection.Name, DisableParallelization = true)]
+public sealed class KernelMemoryCompatStateCollection
+{
+    public const string Name = "KernelMemoryCompatState";
+}
+
+[Collection(KernelMemoryCompatStateCollection.Name)]
 public sealed class KernelMemoryCompatExportsTests
 {
+    private const ulong GuestMemoryBase = 0x1_0000_0000;
+    private const ulong AllocationOutAddress = GuestMemoryBase + 0x100;
+    private const ulong SpanStartOutAddress = GuestMemoryBase + 0x108;
+    private const ulong SpanSizeOutAddress = GuestMemoryBase + 0x110;
+
     [Fact]
     public void PosixStat_MissingFileReturnsMinusOne()
     {
@@ -63,4 +75,93 @@ public sealed class KernelMemoryCompatExportsTests
             CultureInfo.CurrentCulture = previousCulture;
         }
     }
+
+    [Fact]
+    public void AvailableDirectMemorySize_FragmentedRangeReturnsLargestAlignedSpan()
+    {
+        const ulong firstAllocationStart = 0x0020_0000;
+        const ulong firstAllocationLength = 0x0020_0000;
+        const ulong secondAllocationStart = 0x00C0_0000;
+        const ulong secondAllocationLength = 0x0040_0000;
+        var context = new CpuContext(new FakeCpuMemory(GuestMemoryBase, 0x1000), Generation.Gen5);
+
+        try
+        {
+            AllocateDirectMemory(context, firstAllocationStart, firstAllocationLength);
+            AllocateDirectMemory(context, secondAllocationStart, secondAllocationLength);
+
+            QueryAvailableDirectMemory(context, 0, 0x0100_0000, 0x4000);
+
+            Assert.True(context.TryReadUInt64(SpanStartOutAddress, out var spanStart));
+            Assert.True(context.TryReadUInt64(SpanSizeOutAddress, out var spanSize));
+            Assert.Equal(0x0040_0000UL, spanStart);
+            Assert.Equal(0x0080_0000UL, spanSize);
+        }
+        finally
+        {
+            ReleaseDirectMemory(context, firstAllocationStart, firstAllocationLength);
+            ReleaseDirectMemory(context, secondAllocationStart, secondAllocationLength);
+        }
+    }
+
+    [Fact]
+    public void AvailableDirectMemorySize_AppliesAlignmentBeforeComparingSpans()
+    {
+        const ulong allocationStart = 0x0070_0000;
+        const ulong allocationLength = 0x0010_0000;
+        var context = new CpuContext(new FakeCpuMemory(GuestMemoryBase, 0x1000), Generation.Gen5);
+
+        try
+        {
+            AllocateDirectMemory(context, allocationStart, allocationLength);
+
+            QueryAvailableDirectMemory(context, 0x0010_0000, 0x00C0_0000, 0x0040_0000);
+
+            Assert.True(context.TryReadUInt64(SpanStartOutAddress, out var spanStart));
+            Assert.True(context.TryReadUInt64(SpanSizeOutAddress, out var spanSize));
+            Assert.Equal(0x0080_0000UL, spanStart);
+            Assert.Equal(0x0040_0000UL, spanSize);
+        }
+        finally
+        {
+            ReleaseDirectMemory(context, allocationStart, allocationLength);
+        }
+    }
+
+    private static void AllocateDirectMemory(CpuContext context, ulong start, ulong length)
+    {
+        context[CpuRegister.Rdi] = start;
+        context[CpuRegister.Rsi] = start + length;
+        context[CpuRegister.Rdx] = length;
+        context[CpuRegister.Rcx] = 0x4000;
+        context[CpuRegister.R8] = 0;
+        context[CpuRegister.R9] = AllocationOutAddress;
+
+        Assert.Equal(0, KernelMemoryCompatExports.KernelAllocateDirectMemory(context));
+        Assert.True(context.TryReadUInt64(AllocationOutAddress, out var allocatedAddress));
+        Assert.Equal(start, allocatedAddress);
+    }
+
+    private static void QueryAvailableDirectMemory(
+        CpuContext context,
+        ulong searchStart,
+        ulong searchEnd,
+        ulong alignment)
+    {
+        context[CpuRegister.Rdi] = searchStart;
+        context[CpuRegister.Rsi] = searchEnd;
+        context[CpuRegister.Rdx] = alignment;
+        context[CpuRegister.Rcx] = SpanStartOutAddress;
+        context[CpuRegister.R8] = SpanSizeOutAddress;
+
+        Assert.Equal(0, KernelMemoryCompatExports.KernelAvailableDirectMemorySize(context));
+    }
+
+    private static void ReleaseDirectMemory(CpuContext context, ulong start, ulong length)
+    {
+        context[CpuRegister.Rdi] = start;
+        context[CpuRegister.Rsi] = length;
+
+        Assert.Equal(0, KernelMemoryCompatExports.KernelReleaseDirectMemory(context));
+    }
 }