Add pnacl shims to the chrome build.

ppapi/native_client/src/untrusted/pnacl_irt_shim/shim_entry.c

+/*
+ * Copyright (c) 2012 The Chromium 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 "native_client/src/include/elf32.h"
+#include "native_client/src/include/elf_auxv.h"
+#include "native_client/src/include/nacl_macros.h"
+#include "native_client/src/untrusted/pnacl_irt_shim/shim_ppapi.h"
+#include "native_client/src/untrusted/nacl/nacl_startup.h"
+
+
+/*
+ * This is the true entry point for untrusted code.
+ * See nacl_startup.h for the layout at the argument pointer.
+ */
+void _pnacl_wrapper_start(uint32_t *info) {
+  Elf32_auxv_t *auxv = nacl_startup_auxv(info);
+
+  Elf32_auxv_t *entry = NULL;
+  for (Elf32_auxv_t *av = auxv; av->a_type != AT_NULL; ++av) {
+    if (av->a_type == AT_SYSINFO) {
+      entry = av;
+      break;
+    }
+  }
+
+  if (entry != NULL) {
+    /*
+     * Save the real irt interface.
+     */
+    __pnacl_real_irt_interface = (TYPE_nacl_irt_query) entry->a_un.a_val;
+
+    /*
+     * Overwrite the auxv slot with the pnacl IRT shim query function.
+     */
+    entry->a_type = AT_SYSINFO;
+    entry->a_un.a_val = (uintptr_t) __pnacl_irt_interface_wrapper;
+  }
+
+  /* If entry is NULL still allow startup to continue.  It may be the case
+   * that the IRT was not actually used (e.g., for some commandline tests).
+   * For newlib, we can tell that the IRT isn't used when libnacl_sys_private.a
+   * is in the bitcode link line. However, glibc does not use
+   * libnacl_sys_private, so that would not work. We could look for -lppapi
+   * in the bitcode link line, but looking at the bitcode link line
+   * seems brittle (what if the bitcode link was separated from translation).
+   * Thus we always wrap _start, even if there is no IRT auxv entry.
+   */
+
+  /*
+   * Call the user entry point function.  It should not return.
+   * TODO(sehr): Find a way to ensure this is invoked via a tail call.
+   */
+  _start(info);
+}