add: Android 9 support (#117)

This commit makes ReZygisk load Zygisk libraries directly, not utilizing memfd, as it doesn't exist in older versions of Android.

loader/src/common/dl.cpp

@@ -6,6 +6,7 @@
 #include <android/dlext.h>
 
 #include "dl.h"
+#include "files.hpp"
 #include "logging.h"
 
 extern "C" [[gnu::weak]] struct android_namespace_t*
@@ -50,11 +51,22 @@ void* DlopenMem(int fd, int flags) {
         .library_fd = fd
     };
 
-    auto* handle = android_dlopen_ext("/jit-cache-zygisk", flags, &info);
+    /* INFO: We need to find the path of the fd since passing "" to android_dlopen_ext
+        will not work and passing the original "jit-cache-zygisk" will cause a detection again. */
+    char path[PATH_MAX];
+    if (get_path_from_fd(fd, path, sizeof(path)) != 0) {
+        LOGE("Failed to get path for fd: %d", fd);
+        return NULL;
+    }
+        
+    LOGD("Path for fd %d: %s", fd, path);
+
+    auto *handle = android_dlopen_ext(path, flags, &info);
     if (handle) {
         LOGV("dlopen fd %d: %p", fd, handle);
     } else {
         LOGE("dlopen fd %d: %s", fd, dlerror());
     }
+
     return handle;
 }

loader/src/common/files.cpp

@@ -120,3 +120,18 @@ sDIR make_dir(DIR *dp) {
 sFILE make_file(FILE *fp) {
     return sFILE(fp, [](FILE *fp){ return fp ? fclose(fp) : 1; });
 }
+
+int get_path_from_fd(int fd, char *buf, size_t size) {
+    if (fd < 0 || !buf || size == 0) return -1;
+
+    /* NOTE: We assume that the path is always at /data/adb/modules/xxx
+        which should never be longer than 128 chars. */
+    char proc_path[128];
+    snprintf(proc_path, sizeof(proc_path), "/proc/self/fd/%d", fd);
+
+    ssize_t len = readlink(proc_path, buf, size - 1);
+    if (len == -1) return -1;
+
+    buf[len] = '\0';
+    return 0;
+}