gnulib/import/malloca.h

   1 /* Safe automatic memory allocation.
   2    Copyright (C) 2003-2007, 2009-2022 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2003.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 #ifndef _MALLOCA_H
  19 #define _MALLOCA_H
  20
  21 #include <alloca.h>
  22 #include <stddef.h>
  23 #include <stdlib.h>
  24 #include <stdint.h>
  25
  26 #include "xalloc-oversized.h"
  27
  28
  29 #ifdef __cplusplus
  30 extern "C" {
  31 #endif
  32
  33
  34 /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
  35    alloca(N); otherwise it returns NULL.  It either returns N bytes of
  36    memory allocated on the stack, that lasts until the function returns,
  37    or NULL.
  38    Use of safe_alloca should be avoided:
  39      - inside arguments of function calls - undefined behaviour,
  40      - in inline functions - the allocation may actually last until the
  41        calling function returns.
  42 */
  43 #if HAVE_ALLOCA
  44 /* The OS usually guarantees only one guard page at the bottom of the stack,
  45    and a page size can be as small as 4096 bytes.  So we cannot safely
  46    allocate anything larger than 4096 bytes.  Also care for the possibility
  47    of a few compiler-allocated temporary stack slots.
  48    This must be a macro, not a function.  */
  49 # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
  50 #else
  51 # define safe_alloca(N) ((void) (N), NULL)
  52 #endif
  53
  54 /* Free a block of memory allocated through malloca().  */
  55 #if HAVE_ALLOCA
  56 extern void freea (void *p);
  57 #else
  58 # define freea free
  59 #endif
  60
  61 /* malloca(N) is a safe variant of alloca(N).  It allocates N bytes of
  62    memory allocated on the stack, that must be freed using freea() before
  63    the function returns.  Upon failure, it returns NULL.  */
  64 #if HAVE_ALLOCA
  65 # define malloca(N) \
  66   ((N) < 4032 - (2 * sa_alignment_max - 1)                                   \
  67    ? (void *) (((uintptr_t) (char *) alloca ((N) + 2 * sa_alignment_max - 1) \
  68                 + (2 * sa_alignment_max - 1))                                \
  69                & ~(uintptr_t)(2 * sa_alignment_max - 1))                     \
  70    : mmalloca (N))
  71 #else
  72 # define malloca(N) \
  73   mmalloca (N)
  74 #endif
  75 extern void *mmalloca (size_t n)
  76   _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC (freea, 1)
  77   _GL_ATTRIBUTE_ALLOC_SIZE ((1));
  78
  79 /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
  80    It allocates an array of N objects, each with S bytes of memory,
  81    on the stack.  N and S should be nonnegative and free of side effects.
  82    The array must be freed using freea() before the function returns.  */
  83 #define nmalloca(n, s) \
  84   (xalloc_oversized (n, s) ? NULL : malloca ((n) * (size_t) (s)))
  85
  86
  87 #ifdef __cplusplus
  88 }
  89 #endif
  90
  91
  92 /* ------------------- Auxiliary, non-public definitions ------------------- */
  93
  94 /* Determine the alignment of a type at compile time.  */
  95 #if defined __GNUC__ || defined __clang__ || defined __IBM__ALIGNOF__
  96 # define sa_alignof __alignof__
  97 #elif defined __cplusplus
  98   template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
  99 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
 100 #elif defined __hpux
 101   /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
 102      values.  */
 103 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
 104 #elif defined _AIX
 105   /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
 106      values.  */
 107 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
 108 #else
 109 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
 110 #endif
 111
 112 enum
 113 {
 114 /* The desired alignment of memory allocations is the maximum alignment
 115    among all elementary types.  */
 116   sa_alignment_long = sa_alignof (long),
 117   sa_alignment_double = sa_alignof (double),
 118   sa_alignment_longlong = sa_alignof (long long),
 119   sa_alignment_longdouble = sa_alignof (long double),
 120   sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
 121                       | (sa_alignment_longlong - 1)
 122                       | (sa_alignment_longdouble - 1)
 123                      ) + 1
 124 };
 125
 126 #endif /* _MALLOCA_H */