service_runtime/nacl_memory_object.h

   1 /*
   2  * Copyright 2008, Google Inc.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met:
   8  *
   9  *     * Redistributions of source code must retain the above copyright
  10  * notice, this list of conditions and the following disclaimer.
  11  *     * Redistributions in binary form must reproduce the above
  12  * copyright notice, this list of conditions and the following disclaimer
  13  * in the documentation and/or other materials provided with the
  14  * distribution.
  15  *     * Neither the name of Google Inc. nor the names of its
  16  * contributors may be used to endorse or promote products derived from
  17  * this software without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  20  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  21  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  22  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  23  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  24  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  25  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  26  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  27  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  28  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  29  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  30  */
  31
  32 /*
  33  * NaCl Simple/secure ELF loader (NaCl SEL) memory object.
  34  */
  35
  36 #ifndef NATIVE_CLIENT_SERVICE_RUNTIME_MEMORY_OBJECT_H_
  37 #define NATIVE_CLIENT_SERVICE_RUNTIME_MEMORY_OBJECT_H_
  38
  39 #include "native_client/include/nacl_base.h"
  40 #include "native_client/include/portability.h"
  41
  42 #include "native_client/service_runtime/nacl_sync.h"
  43 #include "native_client/service_runtime/nacl_desc_base.h"
  44
  45 #include "native_client/intermodule_comm/nacl_imc_c.h"
  46
  47 EXTERN_C_BEGIN
  48
  49 /*
  50  * Memory object for the virtual memory map.  We map in 64KB chunks,
  51  * and we need this so that we can recreate the memory from the
  52  * original source should we need to move the address space.
  53  *
  54  * This also means that once a descriptor / handle is used to map in
  55  * memory, we cannot close it unless we know how to recreate it.
  56  * Thus, the NaClDesc objects are reference counted.
  57  *
  58  * Any splitting of NaClMemObj objects should be done with the VM map
  59  * lock held, so these NaClMemObj objects do not themselves contain a
  60  * lock.
  61  */
  62
  63 struct NaClMemObj {
  64   struct NaClDesc *ndp;
  65   /*
  66    * The size of the memory object when the mapping took place.  This
  67    * is important becaues the last page in the mapping has to be
  68    * handled especially:
  69    *
  70    * If the object ends in the middle of an allocation, the kernel
  71    * will zero pad the allocation.  The zero bytes are writable, but
  72    * are not reflected back into the file.  First, assume that the
  73    * file size does not change.  This means that for a shared mapping,
  74    * when an address space move occurs we have to re-map the file at
  75    * the new position, and then copy the contents of the rest of the
  76    * allocation to the new location.
  77    *
  78    * If the file has shrunk, then the shared portion between the new
  79    * end of file and the original end of file is impossible to
  80    * duplicate as a shared mapping -- we may need to just crash and
  81    * burn at that point.
  82    *
  83    * If the file has grown, then the unshared portion between the old
  84    * end-of-file and end of that page (assuming it has grown past the
  85    * page boundary) probably should not get overwritten -- and we may
  86    * need to crash and burn at this point as well.
  87    *
  88    * On linux, we could use mremap, but then there's no need: the race
  89    * condition with not being able to atomically update the memory
  90    * mappings doesn't exist.
  91    *
  92    * TODO: figure out exactly what we need to do.
  93    */
  94   off_t           nbytes;  /* stat member is off_t st_size */
  95   /*
  96    * All memory objects that back virtual memory must support
  97    * offset/nbytes mapping.  NB: the VM map code may split a
  98    * NaClMemObj into two if some middle page got unmapped, etc.
  99    */
 100   off_t           offset;
 101 };
 102
 103 /*
 104  * base class ctor and dtor.  NULL != ndp must hold.
 105  */
 106 int NaClMemObjCtor(struct NaClMemObj  *nmop,
 107                    struct NaClDesc    *ndp,
 108                    off_t              nbytes,
 109                    off_t              offset);
 110
 111 int NaClMemObjCopyCtorOff(struct NaClMemObj *nmop,
 112                           struct NaClMemObj *src,
 113                           off_t             additional);
 114
 115 void NaClMemObjDtor(struct NaClMemObj *nmop);
 116
 117 /*
 118  * Allocating Ctor.  Increments refcount on ndp, which must not be NULL.
 119  */
 120 struct NaClMemObj *NaClMemObjMake(struct NaClDesc *ndp,
 121                                   off_t           nbytes,
 122                                   off_t           offset);
 123
 124 struct NaClMemObj *NaClMemObjSplit(struct NaClMemObj  *nmop,
 125                                    off_t              additional);
 126
 127 void NaClMemObjIncOffset(struct NaClMemObj  *nmop,
 128                          off_t              additional);
 129
 130 EXTERN_C_END
 131
 132 #endif