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cxxalloc.h (3174B)

      1 /* This Source Code Form is subject to the terms of the Mozilla Public
      2 * License, v. 2.0. If a copy of the MPL was not distributed with this
      3 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      4 
      5 #ifndef mozilla_cxxalloc_h
      6 #define mozilla_cxxalloc_h
      7 
      8 /*
      9 * We implement the default operators new/delete as part of
     10 * libmozalloc, replacing their definitions in libstdc++.  The
     11 * operator new* definitions in libmozalloc will never return a NULL
     12 * pointer.
     13 *
     14 * Each operator new immediately below returns a pointer to memory
     15 * that can be delete'd by any of
     16 *
     17 *   (1) the matching infallible operator delete immediately below
     18 *   (2) the matching system |operator delete(void*, std::nothrow)|
     19 *   (3) the matching system |operator delete(void*) noexcept(false)|
     20 *
     21 * NB: these are declared |noexcept(false)|, though they will never
     22 * throw that exception.  This declaration is consistent with the rule
     23 * that |::operator new() noexcept(false)| will never return NULL.
     24 *
     25 * NB: mozilla::fallible can be used instead of std::nothrow.
     26 */
     27 
     28 #ifndef MOZALLOC_EXPORT_NEW
     29 #  define MOZALLOC_EXPORT_NEW MFBT_API
     30 #endif
     31 
     32 MOZALLOC_EXPORT_NEW void* operator new(size_t size) noexcept(false) {
     33  return moz_xmalloc(size);
     34 }
     35 
     36 MOZALLOC_EXPORT_NEW void* operator new(size_t size,
     37                                       const std::nothrow_t&) noexcept(true) {
     38  return malloc_impl(size);
     39 }
     40 
     41 MOZALLOC_EXPORT_NEW void* operator new[](size_t size) noexcept(false) {
     42  return moz_xmalloc(size);
     43 }
     44 
     45 // Inlining `new` like this is technically against C++ spec, but we crave perf.
     46 MOZALLOC_EXPORT_NEW void* operator new[](size_t size,
     47                                         const std::nothrow_t&) noexcept(true) {
     48 #if defined(__GNUC__) && !defined(__clang__)
     49 // GCC-14 codegen at -O2 causes false positive due to converting
     50 // `new A[n]` to `malloc(-1)` when `n > PTRDIFF_MAX/sizeof(A)`.
     51 // (See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85783, WONTFIX'd)
     52 #  pragma GCC diagnostic push
     53 #  pragma GCC diagnostic ignored "-Walloc-size-larger-than="
     54 #endif
     55 
     56  return malloc_impl(size);
     57 
     58 #if defined(__GNUC__) && !defined(__clang__)
     59 #  pragma GCC diagnostic pop
     60 #endif
     61 }
     62 
     63 MOZALLOC_EXPORT_NEW void operator delete(void* ptr) noexcept(true) {
     64  return free_impl(ptr);
     65 }
     66 
     67 MOZALLOC_EXPORT_NEW void operator delete(void* ptr,
     68                                         const std::nothrow_t&) noexcept(true) {
     69  return free_impl(ptr);
     70 }
     71 
     72 MOZALLOC_EXPORT_NEW void operator delete[](void* ptr) noexcept(true) {
     73  return free_impl(ptr);
     74 }
     75 
     76 MOZALLOC_EXPORT_NEW void operator delete[](
     77    void* ptr, const std::nothrow_t&) noexcept(true) {
     78  return free_impl(ptr);
     79 }
     80 
     81 #if defined(XP_WIN)
     82 // We provide the global sized delete overloads unconditionally because the
     83 // MSVC runtime headers do, despite compiling with /Zc:sizedDealloc-
     84 MOZALLOC_EXPORT_NEW void operator delete(void* ptr,
     85                                         size_t /*size*/) noexcept(true) {
     86  return free_impl(ptr);
     87 }
     88 
     89 MOZALLOC_EXPORT_NEW void operator delete[](void* ptr,
     90                                           size_t /*size*/) noexcept(true) {
     91  return free_impl(ptr);
     92 }
     93 #endif
     94 
     95 #endif /* mozilla_cxxalloc_h */