Change startup ABI for untrusted code to be C-compatible

src/trusted/service_runtime/arch/arm/nacl_switch_to_app_arm.c

Index: src/trusted/service_runtime/arch/arm/nacl_switch_to_app_arm.c
diff --git a/src/trusted/service_runtime/arch/arm/nacl_switch_to_app_arm.c b/src/trusted/service_runtime/arch/arm/nacl_switch_to_app_arm.c
index 5bd0438d931366f48ca10729a24245232c60cd73..87129dee375e07fbfe3ae831d885b80b466c6587 100644
--- a/src/trusted/service_runtime/arch/arm/nacl_switch_to_app_arm.c
+++ b/src/trusted/service_runtime/arch/arm/nacl_switch_to_app_arm.c
@@ -1,32 +1,7 @@
 /*
- * Copyright 2008, Google Inc.
- * 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.
- *     * Neither the name of Google Inc. nor the names of its
- * contributors may be used to endorse or promote products derived from
- * this software without specific prior written permission.
- *
- * 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.
+ * Copyright (c) 2011 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.
  */
 
 /*
@@ -47,18 +22,27 @@ NORETURN void NaClStartThreadInApp(struct NaClAppThread *natp,
 
   natp->sys.stack_ptr = (NaClGetSp() & ~0xf) + 4;
 
-  /*
-   * springboard pops 4 words from stack which are the parameters for
-   * syscall. In this case, it is not a syscall so no parameters, but we still
-   * need to adjust the stack
-   */
-  natp->user.stack_ptr -= 16;
   nap = natp->nap;
   context = &natp->user;
   context->spring_addr = NaClSysToUser(nap,
                                        nap->mem_start + nap->springboard_addr);
   context->new_eip = new_prog_ctr;
-  context->sysret = 0; /* not used to return */
+
+  /*
+   * At startup this is not the return value, but the first argument.
+   * In the initial thread, it gets the pointer to the information
+   * block on the stack.  Additional threads do not expect anything in
+   * particular in the first argument register, so we don't bother to
+   * conditionalize this.
+   */
+  context->sysret = context->stack_ptr;
+
+  /*
+   * springboard pops 4 words from stack which are the parameters for
+   * syscall. In this case, it is not a syscall so no parameters, but we still
+   * need to adjust the stack
+   */
+  context->stack_ptr -= 16;
 
   NaClSwitch(context);
 }