fixes

core/src/main/java/org/teavm/backend/wasm/WasmGCTarget.java

@@ -321,16 +321,14 @@ public class WasmGCTarget implements TeaVMTarget, TeaVMWasmGCHost {
         customGenerators.contributeToModule(module);
         generateExceptionExports(declarationsGenerator);
         if (enableDirectMallocSupport) {
-            var heapSegment = new WasmMemorySegment();
+            var heapSegmentStart = 0;
             if (!module.getSegments().isEmpty()) {
                 var lastSegment = module.getSegments().get(module.getSegments().size() - 1);
-                heapSegment.setOffset(WasmRuntime.align(lastSegment.getOffset()
-                        + lastSegment.getLength(), WasmHeap.PAGE_SIZE));
+                heapSegmentStart = WasmRuntime.align(lastSegment.getOffset()
+                        + lastSegment.getLength(), WasmHeap.PAGE_SIZE);
             }
-            heapSegment.setLength(WasmHeap.PAGE_SIZE);
-            module.getSegments().add(heapSegment);
-            intrinsics.setupLaxMallocHeap(heapSegment.getOffset(), heapSegment.getOffset() + directMallocMinHeapSize,
-                    heapSegment.getOffset() + directMallocMaxHeapSize);
+            intrinsics.setupLaxMallocHeap(heapSegmentStart, heapSegmentStart + directMallocMinHeapSize,
+                    heapSegmentStart + directMallocMaxHeapSize);
         }
         adjustModuleMemory(module);
 
@@ -439,7 +437,7 @@ public class WasmGCTarget implements TeaVMTarget, TeaVMWasmGCHost {
 
         if (enableDirectMallocSupport) {
             var minPages = (memorySize - 1) / WasmHeap.PAGE_SIZE + 1;
-            var maxPages = (memorySize + directMallocMaxHeapSize - WasmHeap.PAGE_SIZE - 1) / WasmHeap.PAGE_SIZE + 1;
+            var maxPages = minPages + (directMallocMaxHeapSize - 1) / WasmHeap.PAGE_SIZE + 1;
             module.setMinMemorySize(minPages);
             module.setMaxMemorySize(maxPages);
         } else {

core/src/main/java/org/teavm/runtime/LaxMalloc.java

@@ -76,17 +76,19 @@ public final class LaxMalloc {
     private static native void notifyHeapResized();
 
     static {
+        int initialGrowAmount = getHeapMinAddr().toInt() >>> 16;
+        if (growHeapOuter(initialGrowAmount) == -1) {
+            initialGrowAmount = 1;
+            if (growHeapOuter(initialGrowAmount) == -1) {
+                //TODO: Handle failure to initialize fallback 64KiB heap
+            }
+        }
+        
         // zero out the control region
         DirectMalloc.zmemset(addrHeap(0), ADDR_HEAP_DATA_START);
         // initialize heap limit
         addrHeap(ADDR_HEAP_INNER_LIMIT).putAddress(addrHeap(ADDR_HEAP_DATA_START));
-        addrHeap(ADDR_HEAP_OUTER_LIMIT).putAddress(getHeapMinAddr());
-        
-        int initialGrowAmount = getHeapMinAddr().toInt() >>> 16 - 1;
-        if (initialGrowAmount > 0) {
-            //TODO: Need to handle error setting the heap to its initial size
-            growHeapOuter(initialGrowAmount);
-        }
+        addrHeap(ADDR_HEAP_OUTER_LIMIT).putAddress(addrHeap(initialGrowAmount << 16));
     }
 
     /**
@@ -136,7 +138,7 @@ public final class LaxMalloc {
         // need to sbrk
         if (bucketMask == 0L) {
             int sizePlusInts = sizeBytes + 8; // size + 2 ints
-            Address newChunk = growHeap(sizePlusInts); // sbrk
+            Address newChunk = growLastChunk(sizePlusInts);
             
             // Out of memory
             if (newChunk.toInt() == 0) {
@@ -248,7 +250,7 @@ public final class LaxMalloc {
         // no other options, time to sbrk
         
         int sizePlusInts = sizeBytes + 8; // size + 2 ints
-        Address newChunk = growHeap(sizePlusInts); // sbrk
+        Address newChunk = growLastChunk(sizePlusInts);
         
         // Out of memory
         if (newChunk.toInt() == 0) {
@@ -300,7 +302,7 @@ public final class LaxMalloc {
         // no free huge chunks found, time to sbrk
         
         int sizePlusInts = sizeBytes + 8; // size + 2 ints
-        Address newChunk = growHeap(sizePlusInts); // sbrk
+        Address newChunk = growLastChunk(sizePlusInts);
         
         // Out of memory
         if (newChunk.toInt() == 0) {
@@ -514,6 +516,46 @@ public final class LaxMalloc {
         return bucketIndex;
     }
 
+    /**
+     * Removes the last chunk from the heap (if free), then grows the heap by amount minus
+     * the length of the last chunk, this shouldn't be called unless the program has failed
+     * to find a free chunk that is larger than the requested amount
+     */
+    private static Address growLastChunk(int amount) {
+        Address lastAddr = addrHeap(ADDR_HEAP_INNER_LIMIT).getAddress();
+        
+        // make sure it doesn't crash if the heap is empty
+        if (!addrHeap(ADDR_HEAP_DATA_START).isLessThan(lastAddr)) {
+            return growHeap(amount);
+        }
+        
+        // get the length and address of the last chunk 
+        int lastLen = lastAddr.add(-4).getInt();
+        Address lastChunk = lastAddr.add(-lastLen);
+        lastLen = lastChunk.getInt();
+        
+        // check if the last chunk is free
+        if ((lastLen & 0x80000000) == 0) {
+            
+            // chunk is free, attempt to resize the heap first
+            // so errors can be handled
+            if (growHeap(amount - lastLen).toInt() == 0) {
+                // out of memory
+                return Address.fromInt(0);
+            }
+            
+            // unlink last chunk from free list
+            unlinkChunkFromFreeList(lastChunk, lastLen);
+            
+            // return the start of the last chunk
+            return lastChunk;
+        } else {
+            // no free chunk at the end of the heap
+            // just grow the heap by the full amount
+            return growHeap(amount);
+        }
+    }
+
     /**
      * This is our sbrk
      */