Porting memmove() workaround from Realm Java. (#1901)

CHANGELOG.md

@@ -15,7 +15,7 @@ X.Y.Z Release notes
 * Improved performance of `Realm.compact()`.
 
 ### Bug fixes
-* None.
+* [RN Android] Ported workaround for crashes in `memmove`/`memcpy` on some old Android devices (#1163 and #1895).
 
 ### Internals
 * Upgraded to Realm Core v5.6.3.

react-native/android/src/main/jni/Android.mk

@@ -82,6 +82,14 @@ LOCAL_SRC_FILES += src/object-store/src/sync/impl/sync_metadata.cpp
 LOCAL_SRC_FILES += src/object-store/src/sync/impl/work_queue.cpp
 endif
 
+# Workaround for memmove/memcpy bug
+ifeq ($(strip $(TARGET_ARCH_ABI)),armeabi-v7a)
+LOCAL_SRC_FILES += src/android/hack.cpp
+BUILD_WRAP_MEMMOVE = 1
+else
+BUILD_WRAP_MEMMOVE = 0
+endif
+
 LOCAL_C_INCLUDES := src
 LOCAL_C_INCLUDES += src/jsc
 LOCAL_C_INCLUDES += src/object-store/src

react-native/android/src/main/jni/Application.mk

@@ -21,6 +21,15 @@ APP_LDFLAGS += -llog
 APP_LDFLAGS += -landroid
 APP_LDFLAGS += -fvisibility=hidden
 
+# Workaround for memmove/memcpy bug
+ifeq ($(strip $(BUILD_WRAP_MEMMOVE)),1)
+APP_CPPFLAGS += -DREALM_WRAP_MEMMOVE=1
+APP_LDFLAGS += -Wl,--wrap,memmove
+APP_LDFLAGS += -Wl,--wrap,memcpy
+else
+APP_CPPFLAGS += -DREALM_WRAP_MEMMOVE=0
+endif
+
 ifeq ($(strip $(BUILD_TYPE_SYNC)),1)
 APP_CPPFLAGS += -DREALM_ENABLE_SYNC=1
 APP_LDFLAGS += -lz

src/android/hack.cpp

@@ -0,0 +1,116 @@
+/*
+ * Copyright 2017 Realm Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "hack.hpp"
+
+#include <string.h>
+#include <android/log.h>
+
+#include <realm/util/assert.hpp>
+
+#ifndef REALM_WRAP_MEMMOVE
+#error "REALM_WRAP_MEMMOVE is not defined!"
+#endif
+
+#if REALM_WRAP_MEMMOVE
+extern "C" {
+void* __wrap_memmove(void *dest, const void *src, size_t n);
+void* __real_memmove(void *dest, const void *src, size_t n);
+
+void* __wrap_memcpy(void *dest, const void *src, size_t n);
+void* __real_memcpy(void *dest, const void *src, size_t n);
+}
+
+using namespace realm::jni_util;
+
+typedef void* (*MemMoveFunc)(void *dest, const void *src, size_t n);
+static MemMoveFunc s_wrap_memmove_ptr = &__real_memmove;
+static MemMoveFunc s_wrap_memcpy_ptr = &__real_memcpy;
+
+static void* hacked_memmove(void* s1, const void* s2, size_t n)
+{
+    // adapted from https://github.com/dryc/libc11/blob/master/src/string/memmove.c
+    char* dest = (char*)s1;
+    const char* src = (const char*)s2;
+    if (dest <= src) {
+        while (n--) {
+            *dest++ = *src++;
+        }
+    }
+    else {
+        src += n;
+        dest += n;
+        while (n--) {
+            *--dest = *--src;
+        }
+    }
+    return static_cast<void*>(s1);
+}
+
+static void* hacked_memcpy(void* s1, const void* s2, size_t n)
+{
+    // adapted from https://github.com/dryc/libc11/blob/master/src/string/memcpy.c
+    char* dest = (char*)s1;
+    const char* src = (const char*)s2;
+    while (n--) {
+        *dest++ = *src++;
+    }
+    return static_cast<void*>(s1);
+}
+
+void* __wrap_memmove(void *dest, const void *src, size_t n)
+{
+    return (*s_wrap_memmove_ptr)(dest, src, n);
+}
+
+void* __wrap_memcpy(void *dest, const void *src, size_t n)
+{
+    return (*s_wrap_memcpy_ptr)(dest, src, n);
+}
+
+
+// See https://github.com/realm/realm-java/issues/3651#issuecomment-290290228
+// There is a bug in memmove for some Samsung devices which will return "dest-n" instead of dest.
+// The bug was originally found by QT, see https://bugreports.qt.io/browse/QTBUG-34984 .
+// To work around it, we use linker's wrap feature to use a pure C implementation of memmove if the device has the
+// problem.
+static void check_memmove()
+{
+    char* array = strdup("Foobar");
+    size_t len = strlen(array);
+    void* ptr = __real_memmove(array + 1, array, len - 1);
+    if (ptr != array + 1 || strncmp(array, "FFooba", len) != 0) {
+        __android_log_print(ANDROID_LOG_DEBUG, "JSRealm", "memmove is broken on this device. Switching to the builtin implementation.");
+        s_wrap_memmove_ptr = &hacked_memmove;
+        s_wrap_memcpy_ptr  = &hacked_memcpy;
+    }
+    free(array);
+}
+#endif
+
+namespace realm {
+namespace jni_util {
+
+void hack_init()
+{
+#if REALM_WRAP_MEMMOVE
+    check_memmove();
+#endif
+}
+
+}
+}
+

src/android/hack.hpp

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2017 Realm Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef REALM_JNI_UTIL_HACK_HPP
+#define REALM_JNI_UTIL_HACK_HPP
+
+namespace realm {
+namespace jni_util {
+
+// Workaround bugs on some devices.
+void hack_init();
+
+}
+}
+#endif // REALM_JNI_UTIL_HACK_HPP

src/android/io_realm_react_RealmReactModule.cpp

@@ -24,6 +24,7 @@
 #include "rpc.hpp"
 #include "platform.hpp"
 #include "jni_utils.hpp"
+#include "hack.hpp"
 
 using namespace realm::rpc;
 using namespace realm::jni_util;
@@ -39,6 +40,9 @@ namespace realm {
 
 JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm, void*)
 {
+    // Workaround for some known bugs in system calls on specific devices.
+    hack_init();
+
     JNIEnv* env;
     if (vm->GetEnv((void**)&env, JNI_VERSION_1_6) != JNI_OK) {
         return JNI_ERR;