wasm,wasi: make sure buffers returned by malloc are not freed until f… (#3148)

* wasm,wasi: make sure buffers returned by malloc are not freed until free is called

1 files changed, 127 insertions, 0 deletions

diff --git a/tests/runtime_wasi/malloc_test.go b/tests/runtime_wasi/malloc_test.go
new file mode 100644
index 000000000..06b197f13
--- /dev/null
+++ b/tests/runtime_wasi/malloc_test.go
@@ -0,0 +1,127 @@
+//go:build tinygo.wasm
+// +build tinygo.wasm
+
+package runtime_wasi
+
+import (
+	"reflect"
+	"runtime"
+	"strconv"
+	"testing"
+	"unsafe"
+)
+
+//export malloc
+func libc_malloc(size uintptr) unsafe.Pointer
+
+//export free
+func libc_free(ptr unsafe.Pointer)
+
+//export calloc
+func libc_calloc(nmemb, size uintptr) unsafe.Pointer
+
+//export realloc
+func libc_realloc(ptr unsafe.Pointer, size uintptr) unsafe.Pointer
+
+func getFilledBuffer_malloc() uintptr {
+	ptr := libc_malloc(5)
+	fillPanda(ptr)
+	return uintptr(ptr)
+}
+
+func getFilledBuffer_calloc() uintptr {
+	ptr := libc_calloc(2, 5)
+	fillPanda(ptr)
+	*(*byte)(unsafe.Add(ptr, 5)) = 'b'
+	*(*byte)(unsafe.Add(ptr, 6)) = 'e'
+	*(*byte)(unsafe.Add(ptr, 7)) = 'a'
+	*(*byte)(unsafe.Add(ptr, 8)) = 'r'
+	*(*byte)(unsafe.Add(ptr, 9)) = 's'
+	return uintptr(ptr)
+}
+
+func getFilledBuffer_realloc() uintptr {
+	origPtr := getFilledBuffer_malloc()
+	ptr := libc_realloc(unsafe.Pointer(origPtr), 9)
+	*(*byte)(unsafe.Add(ptr, 5)) = 'b'
+	*(*byte)(unsafe.Add(ptr, 6)) = 'e'
+	*(*byte)(unsafe.Add(ptr, 7)) = 'a'
+	*(*byte)(unsafe.Add(ptr, 8)) = 'r'
+	return uintptr(ptr)
+}
+
+func getFilledBuffer_reallocNil() uintptr {
+	ptr := libc_realloc(nil, 5)
+	fillPanda(ptr)
+	return uintptr(ptr)
+}
+
+func fillPanda(ptr unsafe.Pointer) {
+	*(*byte)(unsafe.Add(ptr, 0)) = 'p'
+	*(*byte)(unsafe.Add(ptr, 1)) = 'a'
+	*(*byte)(unsafe.Add(ptr, 2)) = 'n'
+	*(*byte)(unsafe.Add(ptr, 3)) = 'd'
+	*(*byte)(unsafe.Add(ptr, 4)) = 'a'
+}
+
+func checkFilledBuffer(t *testing.T, ptr uintptr, content string) {
+	t.Helper()
+	buf := *(*string)(unsafe.Pointer(&reflect.StringHeader{
+		Data: ptr,
+		Len:  uintptr(len(content)),
+	}))
+	if buf != content {
+		t.Errorf("expected %q, got %q", content, buf)
+	}
+}
+
+func TestMallocFree(t *testing.T) {
+	tests := []struct {
+		name      string
+		getBuffer func() uintptr
+		content   string
+	}{
+		{
+			name:      "malloc",
+			getBuffer: getFilledBuffer_malloc,
+			content:   "panda",
+		},
+		{
+			name:      "calloc",
+			getBuffer: getFilledBuffer_calloc,
+			content:   "pandabears",
+		},
+		{
+			name:      "realloc",
+			getBuffer: getFilledBuffer_realloc,
+			content:   "pandabear",
+		},
+		{
+			name:      "realloc nil",
+			getBuffer: getFilledBuffer_reallocNil,
+			content:   "panda",
+		},
+	}
+
+	for _, tc := range tests {
+		tt := tc
+		t.Run(tt.name, func(t *testing.T) {
+			bufPtr := tt.getBuffer()
+			// Don't use defer to free the buffer as it seems to cause the GC to track it.
+
+			// Churn GC, the pointer should still be valid until free is called.
+			for i := 0; i < 1000; i++ {
+				a := "hello" + strconv.Itoa(i)
+				// Some conditional logic to ensure optimization doesn't remove the loop completely.
+				if len(a) < 0 {
+					break
+				}
+				runtime.GC()
+			}
+
+			checkFilledBuffer(t, bufPtr, tt.content)
+
+			libc_free(unsafe.Pointer(bufPtr))
+		})
+	}
+}