Workaround Go issue causing the app to crash on older Android versions

* Fix app crashes when using Go > 1.23 and Android < 12
* See golang/go#70508

tray/CMakeLists.txt

@@ -412,10 +412,21 @@ if (ANDROID)
     endif ()
 
     if (USE_LIBSYNCTHING)
+        # bundle internal Syncthing library
         set_property(
             TARGET ${META_TARGET_NAME}
             APPEND
             PROPERTY QT_ANDROID_EXTRA_LIBS "${SYNCTHINGINTERNAL_LIBRARY_PATH}")
+
+        # workaround https://github.com/golang/go/issues/70508
+        set(ANDROID_SIGNAL_HANDLER_LIBRARY "androidsignalhandler")
+        add_library("${ANDROID_SIGNAL_HANDLER_LIBRARY}" MODULE android/signalhandler.cpp)
+        find_library(ANDROID_LOG_LIB log)
+        target_link_libraries("${ANDROID_SIGNAL_HANDLER_LIBRARY}" "${ANDROID_LOG_LIB}")
+        set_property(
+            TARGET ${META_TARGET_NAME}
+            APPEND
+            PROPERTY QT_ANDROID_EXTRA_LIBS "${CMAKE_CURRENT_BINARY_DIR}/lib${ANDROID_SIGNAL_HANDLER_LIBRARY}.so")
     endif ()
 
     set(QT_ANDROID_SIGN_APK ON)

tray/android/signalhandler.cpp

@@ -0,0 +1,36 @@
+#include <android/log.h>
+#include <jni.h>
+
+#include <csignal>
+
+#define ST_LIB_LOG_TAG "SyncthingLibrary"
+#define ST_LIB_LOG_INF(...) __android_log_print(ANDROID_LOG_INFO, ST_LIB_LOG_TAG, __VA_ARGS__)
+
+static void handleSigsys(int signum, siginfo_t *info, void *context)
+{
+    // ignore the signal to prevent the app from crashing
+    ST_LIB_LOG_INF("SIGSYS signal received and ignored");
+}
+
+static void initSigsysHandler()
+{
+    struct sigaction sa;
+    sa.sa_flags = SA_SIGINFO;
+    sa.sa_sigaction = handleSigsys;
+    sigemptyset(&sa.sa_mask);
+    if (sigaction(SIGSYS, &sa, nullptr) == -1) {
+        ST_LIB_LOG_INF("Failed to set up SIGSYS handler");
+    } else {
+        ST_LIB_LOG_INF("SIGSYS handler set up successfully");
+    }
+}
+
+extern "C" {
+
+JNIEXPORT void JNICALL
+Java_io_github_martchus_syncthingtray_Activity_initSigsysHandler(JNIEnv *env, jobject thiz)
+{
+    initSigsysHandler();
+}
+
+}

tray/android/src/io/github/martchus/syncthingtray/Activity.java

@@ -130,6 +130,11 @@ public int fontWeightAdjustment() {
     @Override
     public void onCreate(Bundle savedInstanceState) {
         Log.i(TAG, "Creating");
+
+        // workaround https://github.com/golang/go/issues/70508
+        System.loadLibrary("androidsignalhandler");
+        initSigsysHandler();
+
         super.onCreate(savedInstanceState);
 
         // read font scale as Qt does not handle this automatically on Android
@@ -200,4 +205,5 @@ private void sendAndroidIntentToQtQuickApp(String page, boolean fromNotification
 
     private static native void handleAndroidIntent(String page, boolean fromNotification);
     private static native void stopLibSyncthing();
+    private static native void initSigsysHandler();
 }