PNaCl dynamic linking: Build an initial dynamically-linked newlib-based libc

tests/pnacl_dynamic_loading/libc_entry.c

+/*
+ * Copyright (c) 2016 The Native Client Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include <stdlib.h>
+#include <unistd.h>
+
+#include "native_client/src/include/elf32.h"
+#include "native_client/src/untrusted/nacl/nacl_irt.h"
+#include "native_client/src/untrusted/nacl/start.h"
+#include "native_client/src/untrusted/nacl/tls.h"
+
+
+/*
+ * Provide dummy definitions of _init() and _fini() because they are
+ * referenced by libc.a's __libc_init_array(), which we do not use in this
+ * context.
+ */
+
+void _init(void) {
+  abort();
+}
+
+void _fini(void) {
+  abort();
+}
+
+/*
+ * Provide dummy definitions of the TLS layout functions because they are
+ * referenced by libnacl.a's tls.c, which we do not use in this context.
+ */
+
+ptrdiff_t __nacl_tp_tls_offset(size_t tls_size) {
+  abort();
+}
+
+ptrdiff_t __nacl_tp_tdb_offset(size_t tdb_size) {
+  abort();
+}
+
+void __libc_start(int argc, char **argv, char **envp, Elf32_auxv_t *auxv) {
+  environ = envp;
+
+  __libnacl_irt_init(auxv);
+
+  /*
+   * We don't support TLS or pthreads yet, so we skip
+   * __pthread_initialize() for now.
+   */
+  __newlib_thread_init();
+
+  exit(main(argc, argv, envp));
+
+  __builtin_trap();
+}