1*a7c91847Schristos /* Safe automatic memory allocation. 2*a7c91847Schristos Copyright (C) 2003-2004 Free Software Foundation, Inc. 3*a7c91847Schristos Written by Bruno Haible <bruno@clisp.org>, 2003. 4*a7c91847Schristos 5*a7c91847Schristos This program is free software; you can redistribute it and/or modify 6*a7c91847Schristos it under the terms of the GNU General Public License as published by 7*a7c91847Schristos the Free Software Foundation; either version 2, or (at your option) 8*a7c91847Schristos any later version. 9*a7c91847Schristos 10*a7c91847Schristos This program is distributed in the hope that it will be useful, 11*a7c91847Schristos but WITHOUT ANY WARRANTY; without even the implied warranty of 12*a7c91847Schristos MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13*a7c91847Schristos GNU General Public License for more details. 14*a7c91847Schristos 15*a7c91847Schristos You should have received a copy of the GNU General Public License 16*a7c91847Schristos along with this program; if not, write to the Free Software Foundation, 17*a7c91847Schristos Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ 18*a7c91847Schristos 19*a7c91847Schristos #ifndef _ALLOCSA_H 20*a7c91847Schristos #define _ALLOCSA_H 21*a7c91847Schristos 22*a7c91847Schristos #include <alloca.h> 23*a7c91847Schristos #include <stddef.h> 24*a7c91847Schristos #include <stdlib.h> 25*a7c91847Schristos 26*a7c91847Schristos /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call 27*a7c91847Schristos alloca(N); otherwise it returns NULL. It either returns N bytes of 28*a7c91847Schristos memory allocated on the stack, that lasts until the function returns, 29*a7c91847Schristos or NULL. 30*a7c91847Schristos Use of safe_alloca should be avoided: 31*a7c91847Schristos - inside arguments of function calls - undefined behaviour, 32*a7c91847Schristos - in inline functions - the allocation may actually last until the 33*a7c91847Schristos calling function returns. 34*a7c91847Schristos */ 35*a7c91847Schristos #if HAVE_ALLOCA 36*a7c91847Schristos /* The OS usually guarantees only one guard page at the bottom of the stack, 37*a7c91847Schristos and a page size can be as small as 4096 bytes. So we cannot safely 38*a7c91847Schristos allocate anything larger than 4096 bytes. Also care for the possibility 39*a7c91847Schristos of a few compiler-allocated temporary stack slots. 40*a7c91847Schristos This must be a macro, not an inline function. */ 41*a7c91847Schristos # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL) 42*a7c91847Schristos #else 43*a7c91847Schristos # define safe_alloca(N) ((N), NULL) 44*a7c91847Schristos #endif 45*a7c91847Schristos 46*a7c91847Schristos /* allocsa(N) is a safe variant of alloca(N). It allocates N bytes of 47*a7c91847Schristos memory allocated on the stack, that must be freed using freesa() before 48*a7c91847Schristos the function returns. Upon failure, it returns NULL. */ 49*a7c91847Schristos #if HAVE_ALLOCA 50*a7c91847Schristos # define allocsa(N) \ 51*a7c91847Schristos ((N) < 4032 - sa_increment \ 52*a7c91847Schristos ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \ 53*a7c91847Schristos : mallocsa (N)) 54*a7c91847Schristos #else 55*a7c91847Schristos # define allocsa(N) \ 56*a7c91847Schristos mallocsa (N) 57*a7c91847Schristos #endif 58*a7c91847Schristos extern void * mallocsa (size_t n); 59*a7c91847Schristos 60*a7c91847Schristos /* Free a block of memory allocated through allocsa(). */ 61*a7c91847Schristos #if HAVE_ALLOCA 62*a7c91847Schristos extern void freesa (void *p); 63*a7c91847Schristos #else 64*a7c91847Schristos # define freesa free 65*a7c91847Schristos #endif 66*a7c91847Schristos 67*a7c91847Schristos /* Maybe we should also define a variant 68*a7c91847Schristos nallocsa (size_t n, size_t s) - behaves like allocsa (n * s) 69*a7c91847Schristos If this would be useful in your application. please speak up. */ 70*a7c91847Schristos 71*a7c91847Schristos 72*a7c91847Schristos /* ------------------- Auxiliary, non-public definitions ------------------- */ 73*a7c91847Schristos 74*a7c91847Schristos /* Determine the alignment of a type at compile time. */ 75*a7c91847Schristos #if defined __GNUC__ 76*a7c91847Schristos # define sa_alignof __alignof__ 77*a7c91847Schristos #elif defined __cplusplus 78*a7c91847Schristos template <class type> struct sa_alignof_helper { char __slot1; type __slot2; }; 79*a7c91847Schristos # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2) 80*a7c91847Schristos #elif defined __hpux 81*a7c91847Schristos /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof 82*a7c91847Schristos values. */ 83*a7c91847Schristos # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) 84*a7c91847Schristos #else 85*a7c91847Schristos # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) 86*a7c91847Schristos #endif 87*a7c91847Schristos 88*a7c91847Schristos enum 89*a7c91847Schristos { 90*a7c91847Schristos /* The desired alignment of memory allocations is the maximum alignment 91*a7c91847Schristos among all elementary types. */ 92*a7c91847Schristos sa_alignment_long = sa_alignof (long), 93*a7c91847Schristos sa_alignment_double = sa_alignof (double), 94*a7c91847Schristos #ifdef HAVE_LONG_LONG 95*a7c91847Schristos sa_alignment_longlong = sa_alignof (long long), 96*a7c91847Schristos #endif 97*a7c91847Schristos #ifdef HAVE_LONG_DOUBLE 98*a7c91847Schristos sa_alignment_longdouble = sa_alignof (long double), 99*a7c91847Schristos #endif 100*a7c91847Schristos sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1) 101*a7c91847Schristos #ifdef HAVE_LONG_LONG 102*a7c91847Schristos | (sa_alignment_longlong - 1) 103*a7c91847Schristos #endif 104*a7c91847Schristos #ifdef HAVE_LONG_DOUBLE 105*a7c91847Schristos | (sa_alignment_longdouble - 1) 106*a7c91847Schristos #endif 107*a7c91847Schristos ) + 1, 108*a7c91847Schristos /* The increment that guarantees room for a magic word must be >= sizeof (int) 109*a7c91847Schristos and a multiple of sa_alignment_max. */ 110*a7c91847Schristos sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max 111*a7c91847Schristos }; 112*a7c91847Schristos 113*a7c91847Schristos #endif /* _ALLOCSA_H */ 114