engine: android: restore dlsym hack for old Android(<5.0)

engine/platform/android/dlsym-weak.cpp

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2008, 2009 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#ifdef __ANDROID__
+#include <android/log.h>
+#include "linker.h"
+
+static Elf_Sym* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name) {
+    Elf_Sym* symtab = si->symtab;
+    const char* strtab = si->strtab;
+
+    for (unsigned n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]) {
+        Elf_Sym* s = symtab + n;
+        if (strcmp(strtab + s->st_name, name)) continue;
+
+            /* only concern ourselves with global and weak symbol definitions */
+        switch (ELF_ST_BIND(s->st_info)) {
+        case STB_GLOBAL:
+        case STB_WEAK:
+            if (s->st_shndx == SHN_UNDEF) {
+                continue;
+            }
+            return s;
+        }
+    }
+
+    return NULL;
+}
+
+static unsigned elfhash(const char* _name) {
+    const unsigned char* name = (const unsigned char*) _name;
+    unsigned h = 0, g;
+
+    while(*name) {
+        h = (h << 4) + *name++;
+        g = h & 0xf0000000;
+        h ^= g;
+        h ^= g >> 24;
+    }
+    return h;
+}
+
+/* This is used by dlsym(3).  It performs symbol lookup only within the
+   specified soinfo object and not in any of its dependencies.
+
+   TODO: Only looking in the specified soinfo seems wrong. dlsym(3) says
+   that it should do a breadth first search through the dependency
+   tree. This agrees with the ELF spec (aka System V Application
+   Binary Interface) where in Chapter 5 it discuss resolving "Shared
+   Object Dependencies" in breadth first search order.
+ */
+Elf_Sym* dlsym_handle_lookup(soinfo* si, const char* name) {
+    return soinfo_elf_lookup(si, elfhash(name), name);
+}
+
+extern "C" void* dlsym_weak(void* handle, const char* symbol) {
+
+  soinfo* found = NULL;
+  Elf_Sym* sym = NULL;
+  found = reinterpret_cast<soinfo*>(handle);
+  sym = dlsym_handle_lookup(found, symbol);
+
+  if (sym != NULL) {
+    return reinterpret_cast<void*>(sym->st_value + found->base/*load_bias*/);
+  }
+  __android_log_print(ANDROID_LOG_ERROR, "dlsym-weak", "Failed when looking up %s\n", symbol);
+  return NULL;
+}
+#endif