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

   1 /*
   2  * Copyright (c) 2012 The Chromium Authors. All rights reserved.
   3  * Use of this source code is governed by a BSD-style license that can be
   4  * found in the LICENSE file.
   5  */
   6
   7 #include "native_client/src/include/elf32.h"
   8 #include "native_client/src/include/elf_auxv.h"
   9 #include "native_client/src/include/nacl_macros.h"
  10 #include "native_client/src/untrusted/nacl/nacl_startup.h"
  11 #include "ppapi/native_client/src/untrusted/pnacl_irt_shim/shim_ppapi.h"
  12
  13
  14 /*
  15  * This is the true entry point for untrusted code.
  16  * See nacl_startup.h for the layout at the argument pointer.
  17  */
  18 void _pnacl_wrapper_start(uint32_t *info) {
  19   Elf32_auxv_t *auxv = nacl_startup_auxv(info);
  20
  21   Elf32_auxv_t *entry = NULL;
  22   for (Elf32_auxv_t *av = auxv; av->a_type != AT_NULL; ++av) {
  23     if (av->a_type == AT_SYSINFO) {
  24       entry = av;
  25       break;
  26     }
  27   }
  28
  29   if (entry != NULL) {
  30     /*
  31      * Save the real irt interface query function.
  32      */
  33     __pnacl_real_irt_query_func = (TYPE_nacl_irt_query) entry->a_un.a_val;
  34
  35     /*
  36      * Overwrite the auxv slot with the pnacl IRT shim query function.
  37      */
  38     entry->a_type = AT_SYSINFO;
  39     entry->a_un.a_val = (uintptr_t) __pnacl_wrap_irt_query_func;
  40   }
  41
  42   /* If entry is NULL still allow startup to continue.  It may be the case
  43    * that the IRT was not actually used (e.g., for some commandline tests).
  44    * For newlib, we can tell that the IRT isn't used when libnacl_sys_private.a
  45    * is in the bitcode link line. However, glibc does not use
  46    * libnacl_sys_private, so that would not work. We could look for -lppapi
  47    * in the bitcode link line, but looking at the bitcode link line
  48    * seems brittle (what if the bitcode link was separated from translation).
  49    * Thus we always wrap _start, even if there is no IRT auxv entry.
  50    */
  51
  52   /*
  53    * Call the user entry point function.  It should not return.
  54    * TODO(sehr): Find a way to ensure this is invoked via a tail call.
  55    */
  56   _start(info);
  57 }