Home | History | Annotate | Line # | Download | only in gnulib-lib 
      1 /* Safe automatic memory allocation.
      2    Copyright (C) 2003-2006 Free Software Foundation, Inc.
      3    Written by Bruno Haible <bruno (at) 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, write to the Free Software Foundation,
     17    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
     18 
     19 #ifndef _ALLOCSA_H
     20 #define _ALLOCSA_H
     21 
     22 #include <alloca.h>
     23 #include <stddef.h>
     24 #include <stdlib.h>
     25 
     26 
     27 #ifdef __cplusplus
     28 extern "C" {
     29 #endif
     30 
     31 
     32 /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call
     33    alloca(N); otherwise it returns NULL.  It either returns N bytes of
     34    memory allocated on the stack, that lasts until the function returns,
     35    or NULL.
     36    Use of safe_alloca should be avoided:
     37      - inside arguments of function calls - undefined behaviour,
     38      - in inline functions - the allocation may actually last until the
     39        calling function returns.
     40 */
     41 #if HAVE_ALLOCA
     42 /* The OS usually guarantees only one guard page at the bottom of the stack,
     43    and a page size can be as small as 4096 bytes.  So we cannot safely
     44    allocate anything larger than 4096 bytes.  Also care for the possibility
     45    of a few compiler-allocated temporary stack slots.
     46    This must be a macro, not an inline function.  */
     47 # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL)
     48 #else
     49 # define safe_alloca(N) ((N), NULL)
     50 #endif
     51 
     52 /* allocsa(N) is a safe variant of alloca(N).  It allocates N bytes of
     53    memory allocated on the stack, that must be freed using freesa() before
     54    the function returns.  Upon failure, it returns NULL.  */
     55 #if HAVE_ALLOCA
     56 # define allocsa(N) \
     57   ((N) < 4032 - sa_increment					    \
     58    ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \
     59    : mallocsa (N))
     60 #else
     61 # define allocsa(N) \
     62   mallocsa (N)
     63 #endif
     64 extern void * mallocsa (size_t n);
     65 
     66 /* Free a block of memory allocated through allocsa().  */
     67 #if HAVE_ALLOCA
     68 extern void freesa (void *p);
     69 #else
     70 # define freesa free
     71 #endif
     72 
     73 /* Maybe we should also define a variant
     74     nallocsa (size_t n, size_t s) - behaves like allocsa (n * s)
     75    If this would be useful in your application. please speak up.  */
     76 
     77 
     78 #ifdef __cplusplus
     79 }
     80 #endif
     81 
     82 
     83 /* ------------------- Auxiliary, non-public definitions ------------------- */
     84 
     85 /* Determine the alignment of a type at compile time.  */
     86 #if defined __GNUC__
     87 # define sa_alignof __alignof__
     88 #elif defined __cplusplus
     89   template <class type> struct sa_alignof_helper { char __slot1; type __slot2; };
     90 # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2)
     91 #elif defined __hpux
     92   /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof
     93      values.  */
     94 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
     95 #elif defined _AIX
     96   /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof
     97      values.  */
     98 # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8)
     99 #else
    100 # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2)
    101 #endif
    102 
    103 enum
    104 {
    105 /* The desired alignment of memory allocations is the maximum alignment
    106    among all elementary types.  */
    107   sa_alignment_long = sa_alignof (long),
    108   sa_alignment_double = sa_alignof (double),
    109 #ifdef HAVE_LONG_LONG_INT
    110   sa_alignment_longlong = sa_alignof (long long),
    111 #endif
    112 #ifdef HAVE_LONG_DOUBLE
    113   sa_alignment_longdouble = sa_alignof (long double),
    114 #endif
    115   sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1)
    116 #ifdef HAVE_LONG_LONG_INT
    117 		      | (sa_alignment_longlong - 1)
    118 #endif
    119 #ifdef HAVE_LONG_DOUBLE
    120 		      | (sa_alignment_longdouble - 1)
    121 #endif
    122 		     ) + 1,
    123 /* The increment that guarantees room for a magic word must be >= sizeof (int)
    124    and a multiple of sa_alignment_max.  */
    125   sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max
    126 };
    127 
    128 #endif /* _ALLOCSA_H */
    129