Change the pnacl shim from doing real shimming to just intercepting

src/untrusted/pnacl_irt_shim/shim_entry.c

 /*
- * Copyright (c) 2011 The Native Client Authors. All rights reserved.
+ * Copyright 2011 The Native Client Authors. All rights reserved.

[jvoung (off chromium), 2012/08/27 21:57:39]

Is the new copyright header not supposed to have a (c), or was that an accident?

[Robert Muth (chromium), 2012/08/27 22:38:18]

yes, "(c)" is meaningless I was told

  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
+#include <stddef.h>
 #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/irt/irt.h"
 #include "native_client/src/untrusted/nacl/nacl_startup.h"
 
+/*
+ * For more information about this hack cf.
+ * src/untrusted/irt/irt_ppapi.c
+ */
+
+static TYPE_nacl_irt_query real_irt_interface;
+
+/* cf. src/untrusted/irt/irt.h  NACL_IRT_PPAPIHOOK_(SHIMMED_)v0_1 */
+char prefix_search[] = "nacl-irt-ppapihook";

[jvoung (off chromium), 2012/08/27 21:57:39]

static const ?

[Robert Muth (chromium), 2012/08/27 22:38:18]

Done.

+char prefix_replace[] = "nacl-irt-ppapihook-shimmed";
+
+int my_strcmp(const char* s1, const char* s2) {

[jvoung (off chromium), 2012/08/27 21:57:39]

Comments about why we provide a custom strcmp, strcpy.

Make them "static" ?

[Robert Muth (chromium), 2012/08/27 22:38:18]

Done.

+  while( *s1 != '\0' && *s2 != '\0' && *s1 == *s2) {
+    s1++;
+    s2++;
+  }
+  return *s1 - *s2;
+}
+
+void my_strpy(char* s1, const char* s2) {

[jvoung (off chromium), 2012/08/27 21:57:39]

my_strcpy

[Robert Muth (chromium), 2012/08/27 22:38:18]

Done.

+  while( *s2 != '\0') {

[jvoung (off chromium), 2012/08/27 21:57:39]

"strcpy"

extra space in front of *s2.

[Robert Muth (chromium), 2012/08/27 22:38:18]

Done.

+    *s1 = *s2;
+    s1++;
+    s2++;
+  }
+  *s1 = '\0';
+}
+
+static size_t pnacl_irt_interface_interceptor(const char *interface_ident,
+                                              void *table, size_t tablesize) {
+  /* make this big enough to hold prefix_replace + version suffix */
+  char buffer[2 * sizeof(prefix_replace)];
+
+  const char* ident = interface_ident;
+  /* rewrite: "nacl-irt-ppapihook-XXX" -> "nacl-irt-ppapihook-shimmed-XXX" */
+  if (0 == my_strcmp(interface_ident, prefix_search)) {
+    /* but  not if it is already  "nacl-irt-ppapihook-shimmed-XXX" */

[jvoung (off chromium), 2012/08/27 21:57:39]

extra space "but  not"

[Robert Muth (chromium), 2012/08/27 22:38:18]

Done.

+    if (0 != my_strcmp(interface_ident, prefix_replace)) {
+      my_strpy(buffer, prefix_replace);
+      my_strpy(buffer + sizeof(prefix_replace) - 1,
+               interface_ident + sizeof(prefix_search) - 1);
+      ident = buffer;
+    }
+  }
+  return real_irt_interface(ident, table, tablesize);
+}
 
 /*
  * 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;
+    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;
+    entry->a_un.a_val = (uintptr_t) pnacl_irt_interface_interceptor;
   }
 
   /* 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);
 }