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      1 /* Safe automatic memory allocation.
      2    Copyright (C) 2003-2007, 2009-2022 Free Software Foundation, Inc.
      3    Written by Bruno Haible <bruno (at) 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 */
    127