Use XDG basedir spec on Linux

diff --git a/java/zylib/src/main/java/com/google/security/zynamics/zylib/system/SystemHelpers.java b/java/zylib/src/main/java/com/google/security/zynamics/zylib/system/SystemHelpers.java
index aa8754b9..eddf021c 100644
--- a/java/zylib/src/main/java/com/google/security/zynamics/zylib/system/SystemHelpers.java
+++ b/java/zylib/src/main/java/com/google/security/zynamics/zylib/system/SystemHelpers.java
@@ -38,7 +38,7 @@ public final class SystemHelpers {
       // Win32 function.
       result = System.getenv("ProgramData");
     } else if (isRunningLinux()) {
-      result = "/etc/opt";
+      result = "/etc/xdg";
     } else if (isRunningMacOSX()) {
       result = "/Library/Application Support";
     } else {
@@ -76,9 +76,15 @@ public final class SystemHelpers {
       // function.
       result = System.getenv("APPDATA");
     } else {
-      result = System.getProperty("user.home");
-      if (isRunningMacOSX()) {
-        result += "/Library/Application Support";
+      result = System.getenv("XDG_DATA_HOME");
+      if (result == null || !result.startsWith("/")) {
+        result = System.getProperty("user.home");
+        if (isRunningLinux()) {
+            result += "/.local/share";
+        }
+        if (isRunningMacOSX()) { // Since there isn't a standard way to get this path on macOS (at least I'm not aware of), should we also put this codepath in here?
+          result += "/Library/Application Support";
+        }
       }
     }
     return FileUtils.ensureTrailingSlash(result);
@@ -93,7 +99,7 @@ public final class SystemHelpers {
    */
   public static String getApplicationDataDirectory(final String product) {
     return getApplicationDataDirectory()
-        + (isRunningLinux() ? "." + product.toLowerCase() : product)
+        + (isRunningLinux() ? product.toLowerCase() : product)
         + File.separator;
   }
 

diff --git a/util/process.cc b/util/process.cc
index 6fdeb42..bc46b04 100644
--- a/util/process.cc
+++ b/util/process.cc
@@ -241,15 +241,25 @@ absl::StatusOr<std::string> GetOrCreateAppDataDirectory(
     absl::string_view product_name) {
   std::string path;
 #ifndef _WIN32
-  const char* home_dir = getenv("HOME");
-  if (!home_dir) {
-    return absl::NotFoundError("Home directory not set");
+  std::string data_home;
+  const char* data_home_env = getenv("XDG_DATA_HOME");
+  if (data_home_env && data_home_env[0] == '/') {
+    data_home = data_home_env;
+  } else {
+    const char* home_dir = getenv("HOME");
+    if (!home_dir) {
+      return absl::NotFoundError("Home directory not set");
+    }
+#ifdef __APPLE__
+    data_home = JoinPath(home_dir, "Library", "Application Support");
+#else
+    data_home = JoinPath(home_dir, ".local", "share");
+#endif  // __APPLE__
   }
 #ifdef __APPLE__
-  path = JoinPath(home_dir, "Library", "Application Support", product_name);
+  path = JoinPath(data_home, product_name);
 #else
-  path = JoinPath(home_dir,
-                  absl::StrCat(".", absl::AsciiStrToLower(product_name)));
+  path = JoinPath(data_home, absl::AsciiStrToLower(product_name));
 #endif  // __APPLE__
 #else
   char buffer[MAX_PATH] = {0};
@@ -270,7 +280,7 @@ absl::StatusOr<std::string> GetCommonAppDataDirectory(
 #ifdef __APPLE__
   path = JoinPath("/Library", "Application Support", product_name);
 #else
-  path = JoinPath("/etc/opt/", absl::AsciiStrToLower(product_name));
+  path = JoinPath("/etc", "xdg", absl::AsciiStrToLower(product_name));
 #endif  // __APPLE__
 #else
   char buffer[MAX_PATH] = {0};