lib/malloca.h

   1 /* Safe automatic memory allocation.
   2    Copyright (C) 2003-2007, 2009-2019 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2003.
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2, or (at your option)
   8    any later version.
   9
  10    This program 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 General Public License for more details.
  14
  15    You should have received a copy of the GNU 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 /* malloca(N) is a safe variant of alloca(N).  It allocates N bytes of
  55    memory allocated on the stack, that must be freed using freea() before
  56    the function returns.  Upon failure, it returns NULL.  */
  57 #if HAVE_ALLOCA
  58 # define malloca(N) \
  59   ((N) < 4032 - (2 * sa_alignment_max - 1)                                   \
  60    ? (void *) (((uintptr_t) (char *) alloca ((N) + 2 * sa_alignment_max - 1) \
  61                 + (2 * sa_alignment_max - 1))                                \
  62                & ~(uintptr_t)(2 * sa_alignment_max - 1))                     \
  63    : mmalloca (N))
  64 #else
  65 # define malloca(N) \
  66   mmalloca (N)
  67 #endif
  68 extern void * mmalloca (size_t n);
  69
  70 /* Free a block of memory allocated through malloca().  */
  71 #if HAVE_ALLOCA
  72 extern void freea (void *p);
  73 #else
  74 # define freea free
  75 #endif
  76
  77 /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
  78    It allocates an array of N objects, each with S bytes of memory,
  79    on the stack.  S must be positive and N must be nonnegative.
  80    The array must be freed using freea() before the function returns.  */
  81 #define nmalloca(n, s) (xalloc_oversized (n, s) ? NULL : malloca ((n) * (s)))
  82
  83
  84 #ifdef __cplusplus
  85 }
  86 #endif
  87
  88
  89 /* ------------------- Auxiliary, non-public definitions ------------------- */
  90
  91 /* Determine the alignment of a type at compile time.  */
  92 #if defined __GNUC__ || defined __IBM__ALIGNOF__
  93 # define sa_alignof __alignof__
  94 #elif defined __cplusplus
  95   template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
  96 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
  97 #elif defined __hpux
  98   /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
  99      values.  */
 100 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
 101 #elif defined _AIX
 102   /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
 103      values.  */
 104 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
 105 #else
 106 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
 107 #endif
 108
 109 enum
 110 {
 111 /* The desired alignment of memory allocations is the maximum alignment
 112    among all elementary types.  */
 113   sa_alignment_long = sa_alignof (long),
 114   sa_alignment_double = sa_alignof (double),
 115 #if HAVE_LONG_LONG_INT
 116   sa_alignment_longlong = sa_alignof (long long),
 117 #endif
 118   sa_alignment_longdouble = sa_alignof (long double),
 119   sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
 120 #if HAVE_LONG_LONG_INT
 121                       | (sa_alignment_longlong - 1)
 122 #endif
 123                       | (sa_alignment_longdouble - 1)
 124                      ) + 1
 125 };
 126
 127 #endif /* _MALLOCA_H */