lib/malloca.h

   1 /* Safe automatic memory allocation.
   2    Copyright (C) 2003-2007, 2009-2024 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 /* This file uses _GL_ATTRIBUTE_ALLOC_SIZE, _GL_ATTRIBUTE_DEALLOC,
  22    _GL_ATTRIBUTE_MALLOC, HAVE_ALLOCA.  */
  23 #if !_GL_CONFIG_H_INCLUDED
  24  #error "Please include config.h first."
  25 #endif
  26
  27 #include <alloca.h>
  28 #include <stddef.h>
  29 #include <stdlib.h>
  30 #include <stdint.h>
  31 #if defined __CHERI_PURE_CAPABILITY__
  32 # include <cheri.h>
  33 #endif
  34
  35 #include "xalloc-oversized.h"
  36
  37
  38 #ifdef __cplusplus
  39 extern "C" {
  40 #endif
  41
  42
  43 /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
  44    alloca(N); otherwise it returns NULL.  It either returns N bytes of
  45    memory allocated on the stack, that lasts until the function returns,
  46    or NULL.
  47    Use of safe_alloca should be avoided:
  48      - inside arguments of function calls - undefined behaviour,
  49      - in inline functions - the allocation may actually last until the
  50        calling function returns.
  51 */
  52 #if HAVE_ALLOCA
  53 /* The OS usually guarantees only one guard page at the bottom of the stack,
  54    and a page size can be as small as 4096 bytes.  So we cannot safely
  55    allocate anything larger than 4096 bytes.  Also care for the possibility
  56    of a few compiler-allocated temporary stack slots.
  57    This must be a macro, not a function.  */
  58 # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
  59 #else
  60 # define safe_alloca(N) ((void) (N), NULL)
  61 #endif
  62
  63 /* Free a block of memory allocated through malloca().  */
  64 #if HAVE_ALLOCA
  65 extern void freea (void *p);
  66 #else
  67 # define freea free
  68 #endif
  69
  70 /* malloca(N) is a safe variant of alloca(N).  It allocates N bytes of
  71    memory allocated on the stack, that must be freed using freea() before
  72    the function returns.  Upon failure, it returns NULL.  */
  73 #if HAVE_ALLOCA
  74 # if defined __CHERI_PURE_CAPABILITY__
  75 #  define malloca(N) \
  76     ((N) < 4032 - (2 * sa_alignment_max - 1)                                  \
  77      ? cheri_bounds_set ((void *) (((uintptr_t)                               \
  78                                      (char *)                                 \
  79                                       alloca ((N) + 2 * sa_alignment_max - 1) \
  80                                     + (2 * sa_alignment_max - 1))             \
  81                                    & ~(uintptr_t)(2 * sa_alignment_max - 1)), \
  82                          (N))                                                 \
  83      : mmalloca (N))
  84 # else
  85 #  define malloca(N) \
  86     ((N) < 4032 - (2 * sa_alignment_max - 1)                                   \
  87      ? (void *) (((uintptr_t) (char *) alloca ((N) + 2 * sa_alignment_max - 1) \
  88                   + (2 * sa_alignment_max - 1))                                \
  89                  & ~(uintptr_t)(2 * sa_alignment_max - 1))                     \
  90      : mmalloca (N))
  91 # endif
  92 #else
  93 # define malloca(N) \
  94   mmalloca (N)
  95 #endif
  96 extern void *mmalloca (size_t n)
  97   _GL_ATTRIBUTE_MALLOC _GL_ATTRIBUTE_DEALLOC (freea, 1)
  98   _GL_ATTRIBUTE_ALLOC_SIZE ((1));
  99
 100 /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S).
 101    It allocates an array of N objects, each with S bytes of memory,
 102    on the stack.  N and S should be nonnegative and free of side effects.
 103    The array must be freed using freea() before the function returns.  */
 104 #define nmalloca(n, s) \
 105   (xalloc_oversized (n, s) ? NULL : malloca ((n) * (size_t) (s)))
 106
 107
 108 #ifdef __cplusplus
 109 }
 110 #endif
 111
 112
 113 /* ------------------- Auxiliary, non-public definitions ------------------- */
 114
 115 /* Determine the alignment of a type at compile time.  */
 116 #if defined __GNUC__ || defined __clang__ || defined __IBM__ALIGNOF__
 117 # define sa_alignof __alignof__
 118 #elif defined __cplusplus
 119   template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
 120 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
 121 #elif defined __hpux
 122   /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
 123      values.  */
 124 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
 125 #elif defined _AIX
 126   /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
 127      values.  */
 128 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
 129 #else
 130 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
 131 #endif
 132
 133 enum
 134 {
 135 /* The desired alignment of memory allocations is the maximum alignment
 136    among all elementary types.  */
 137   sa_alignment_long = sa_alignof (long),
 138   sa_alignment_double = sa_alignof (double),
 139   sa_alignment_longlong = sa_alignof (long long),
 140   sa_alignment_longdouble = sa_alignof (long double),
 141   sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
 142                       | (sa_alignment_longlong - 1)
 143                       | (sa_alignment_longdouble - 1)
 144                      ) + 1
 145 };
 146
 147 #endif /* _MALLOCA_H */