The Tor Browser: mfbt/PodOperations.h@97036ab72558 (annotated)

mfbt/PodOperations.h@97036ab72558 (annotated)

mfbt/PodOperations.h

Tue, 06 Jan 2015 21:39:09 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Tue, 06 Jan 2015 21:39:09 +0100
branch: TOR_BUG_9701
changeset 8: 97036ab72558
permissions: -rw-r--r--

Conditionally force memory storage according to privacy.thirdparty.isolate;
This solves Tor bug #9701, complying with disk avoidance documented in
https://www.torproject.org/projects/torbrowser/design/#disk-avoidance.

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 /*
  * Operations for zeroing POD types, arrays, and so on.
  *
  * These operations are preferable to memset, memcmp, and the like because they
  * don't require remembering to multiply by sizeof(T), array lengths, and so on
  * everywhere.
  */
 #ifndef mozilla_PodOperations_h
 #define mozilla_PodOperations_h
 #include "mozilla/Array.h"
 #include "mozilla/ArrayUtils.h"
 #include "mozilla/Attributes.h"
 #include <stdint.h>
 #include <string.h>
 namespace mozilla {
 /** Set the contents of |t| to 0. */
 template<typename T>
 static MOZ_ALWAYS_INLINE void
 PodZero(T* t)
 {
   memset(t, 0, sizeof(T));
 }
 /** Set the contents of |nelem| elements starting at |t| to 0. */
 template<typename T>
 static MOZ_ALWAYS_INLINE void
 PodZero(T* t, size_t nelem)
 {
   /*
    * This function is often called with 'nelem' small; we use an inline loop
    * instead of calling 'memset' with a non-constant length.  The compiler
    * should inline the memset call with constant size, though.
    */
   for (T* end = t + nelem; t < end; t++)
     memset(t, 0, sizeof(T));
 }
 /*
  * Arrays implicitly convert to pointers to their first element, which is
  * dangerous when combined with the above PodZero definitions.  Adding an
  * overload for arrays is ambiguous, so we need another identifier.  The
  * ambiguous overload is left to catch mistaken uses of PodZero; if you get a
  * compile error involving PodZero and array types, use PodArrayZero instead.
  */
 template<typename T, size_t N>
 static void PodZero(T (&t)[N]) MOZ_DELETE;
 template<typename T, size_t N>
 static void PodZero(T (&t)[N], size_t nelem) MOZ_DELETE;
 /** Set the contents of the array |t| to zero. */
 template <class T, size_t N>
 static MOZ_ALWAYS_INLINE void
 PodArrayZero(T (&t)[N])
 {
   memset(t, 0, N * sizeof(T));
 }
 template <typename T, size_t N>
 static MOZ_ALWAYS_INLINE void
 PodArrayZero(Array<T, N>& arr)
 {
   memset(&arr[0], 0, N * sizeof(T));
 }
 /**
  * Assign |*src| to |*dst|.  The locations must not be the same and must not
  * overlap.
  */
 template<typename T>
 static MOZ_ALWAYS_INLINE void
 PodAssign(T* dst, const T* src)
 {
   MOZ_ASSERT(dst != src);
   MOZ_ASSERT_IF(src < dst, PointerRangeSize(src, static_cast<const T*>(dst)) >= 1);
   MOZ_ASSERT_IF(dst < src, PointerRangeSize(static_cast<const T*>(dst), src) >= 1);
   memcpy(reinterpret_cast<char*>(dst), reinterpret_cast<const char*>(src), sizeof(T));
 }
 /**
  * Copy |nelem| T elements from |src| to |dst|.  The two memory ranges must not
  * overlap!
  */
 template<typename T>
 static MOZ_ALWAYS_INLINE void
 PodCopy(T* dst, const T* src, size_t nelem)
 {
   MOZ_ASSERT(dst != src);
   MOZ_ASSERT_IF(src < dst, PointerRangeSize(src, static_cast<const T*>(dst)) >= nelem);
   MOZ_ASSERT_IF(dst < src, PointerRangeSize(static_cast<const T*>(dst), src) >= nelem);
   if (nelem < 128) {
     /*
      * Avoid using operator= in this loop, as it may have been
      * intentionally deleted by the POD type.
      */
     for (const T* srcend = src + nelem; src < srcend; src++, dst++)
       PodAssign(dst, src);
   } else {
     memcpy(dst, src, nelem * sizeof(T));
   }
 }
 template<typename T>
 static MOZ_ALWAYS_INLINE void
 PodCopy(volatile T* dst, const volatile T* src, size_t nelem)
 {
   MOZ_ASSERT(dst != src);
   MOZ_ASSERT_IF(src < dst,
                 PointerRangeSize(src, static_cast<const volatile T*>(dst)) >= nelem);
   MOZ_ASSERT_IF(dst < src,
                 PointerRangeSize(static_cast<const volatile T*>(dst), src) >= nelem);
   /*
    * Volatile |dst| requires extra work, because it's undefined behavior to
    * modify volatile objects using the mem* functions.  Just write out the
    * loops manually, using operator= rather than memcpy for the same reason,
    * and let the compiler optimize to the extent it can.
    */
   for (const volatile T* srcend = src + nelem; src < srcend; src++, dst++)
     *dst = *src;
 }
 /*
  * Copy the contents of the array |src| into the array |dst|, both of size N.
  * The arrays must not overlap!
  */
 template <class T, size_t N>
 static MOZ_ALWAYS_INLINE void
 PodArrayCopy(T (&dst)[N], const T (&src)[N])
 {
   PodCopy(dst, src, N);
 }
 /**
  * Copy the memory for |nelem| T elements from |src| to |dst|.  If the two
  * memory ranges overlap, then the effect is as if the |nelem| elements are
  * first copied from |src| to a temporary array, and then from the temporary
  * array to |dst|.
  */
 template<typename T>
 static MOZ_ALWAYS_INLINE void
 PodMove(T* dst, const T* src, size_t nelem)
 {
   MOZ_ASSERT(nelem <= SIZE_MAX / sizeof(T),
              "trying to move an impossible number of elements");
   memmove(dst, src, nelem * sizeof(T));
 }
 /**
  * Determine whether the |len| elements at |one| are memory-identical to the
  * |len| elements at |two|.
  */
 template<typename T>
 static MOZ_ALWAYS_INLINE bool
 PodEqual(const T* one, const T* two, size_t len)
 {
   if (len < 128) {
     const T* p1end = one + len;
     const T* p1 = one;
     const T* p2 = two;
     for (; p1 < p1end; p1++, p2++) {
       if (*p1 != *p2)
         return false;
     }
     return true;
   }
   return !memcmp(one, two, len * sizeof(T));
 }
 } // namespace mozilla
 #endif /* mozilla_PodOperations_h */

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mfbt/PodOperations.h@97036ab72558 (annotated)

mfbt/PodOperations.h