1*63eb84d1Schristos /* Safe automatic memory allocation. 2*63eb84d1Schristos Copyright (C) 2003-2006 Free Software Foundation, Inc. 3*63eb84d1Schristos Written by Bruno Haible <bruno@clisp.org>, 2003. 4*63eb84d1Schristos 5*63eb84d1Schristos This program is free software; you can redistribute it and/or modify 6*63eb84d1Schristos it under the terms of the GNU General Public License as published by 7*63eb84d1Schristos the Free Software Foundation; either version 2, or (at your option) 8*63eb84d1Schristos any later version. 9*63eb84d1Schristos 10*63eb84d1Schristos This program is distributed in the hope that it will be useful, 11*63eb84d1Schristos but WITHOUT ANY WARRANTY; without even the implied warranty of 12*63eb84d1Schristos MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13*63eb84d1Schristos GNU General Public License for more details. 14*63eb84d1Schristos 15*63eb84d1Schristos You should have received a copy of the GNU General Public License 16*63eb84d1Schristos along with this program; if not, write to the Free Software Foundation, 17*63eb84d1Schristos Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ 18*63eb84d1Schristos 19*63eb84d1Schristos #ifndef _ALLOCSA_H 20*63eb84d1Schristos #define _ALLOCSA_H 21*63eb84d1Schristos 22*63eb84d1Schristos #include <alloca.h> 23*63eb84d1Schristos #include <stddef.h> 24*63eb84d1Schristos #include <stdlib.h> 25*63eb84d1Schristos 26*63eb84d1Schristos 27*63eb84d1Schristos #ifdef __cplusplus 28*63eb84d1Schristos extern "C" { 29*63eb84d1Schristos #endif 30*63eb84d1Schristos 31*63eb84d1Schristos 32*63eb84d1Schristos /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call 33*63eb84d1Schristos alloca(N); otherwise it returns NULL. It either returns N bytes of 34*63eb84d1Schristos memory allocated on the stack, that lasts until the function returns, 35*63eb84d1Schristos or NULL. 36*63eb84d1Schristos Use of safe_alloca should be avoided: 37*63eb84d1Schristos - inside arguments of function calls - undefined behaviour, 38*63eb84d1Schristos - in inline functions - the allocation may actually last until the 39*63eb84d1Schristos calling function returns. 40*63eb84d1Schristos */ 41*63eb84d1Schristos #if HAVE_ALLOCA 42*63eb84d1Schristos /* The OS usually guarantees only one guard page at the bottom of the stack, 43*63eb84d1Schristos and a page size can be as small as 4096 bytes. So we cannot safely 44*63eb84d1Schristos allocate anything larger than 4096 bytes. Also care for the possibility 45*63eb84d1Schristos of a few compiler-allocated temporary stack slots. 46*63eb84d1Schristos This must be a macro, not an inline function. */ 47*63eb84d1Schristos # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL) 48*63eb84d1Schristos #else 49*63eb84d1Schristos # define safe_alloca(N) ((N), NULL) 50*63eb84d1Schristos #endif 51*63eb84d1Schristos 52*63eb84d1Schristos /* allocsa(N) is a safe variant of alloca(N). It allocates N bytes of 53*63eb84d1Schristos memory allocated on the stack, that must be freed using freesa() before 54*63eb84d1Schristos the function returns. Upon failure, it returns NULL. */ 55*63eb84d1Schristos #if HAVE_ALLOCA 56*63eb84d1Schristos # define allocsa(N) \ 57*63eb84d1Schristos ((N) < 4032 - sa_increment \ 58*63eb84d1Schristos ? (void *) ((char *) alloca ((N) + sa_increment) + sa_increment) \ 59*63eb84d1Schristos : mallocsa (N)) 60*63eb84d1Schristos #else 61*63eb84d1Schristos # define allocsa(N) \ 62*63eb84d1Schristos mallocsa (N) 63*63eb84d1Schristos #endif 64*63eb84d1Schristos extern void * mallocsa (size_t n); 65*63eb84d1Schristos 66*63eb84d1Schristos /* Free a block of memory allocated through allocsa(). */ 67*63eb84d1Schristos #if HAVE_ALLOCA 68*63eb84d1Schristos extern void freesa (void *p); 69*63eb84d1Schristos #else 70*63eb84d1Schristos # define freesa free 71*63eb84d1Schristos #endif 72*63eb84d1Schristos 73*63eb84d1Schristos /* Maybe we should also define a variant 74*63eb84d1Schristos nallocsa (size_t n, size_t s) - behaves like allocsa (n * s) 75*63eb84d1Schristos If this would be useful in your application. please speak up. */ 76*63eb84d1Schristos 77*63eb84d1Schristos 78*63eb84d1Schristos #ifdef __cplusplus 79*63eb84d1Schristos } 80*63eb84d1Schristos #endif 81*63eb84d1Schristos 82*63eb84d1Schristos 83*63eb84d1Schristos /* ------------------- Auxiliary, non-public definitions ------------------- */ 84*63eb84d1Schristos 85*63eb84d1Schristos /* Determine the alignment of a type at compile time. */ 86*63eb84d1Schristos #if defined __GNUC__ 87*63eb84d1Schristos # define sa_alignof __alignof__ 88*63eb84d1Schristos #elif defined __cplusplus 89*63eb84d1Schristos template <class type> struct sa_alignof_helper { char __slot1; type __slot2; }; 90*63eb84d1Schristos # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2) 91*63eb84d1Schristos #elif defined __hpux 92*63eb84d1Schristos /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof 93*63eb84d1Schristos values. */ 94*63eb84d1Schristos # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) 95*63eb84d1Schristos #elif defined _AIX 96*63eb84d1Schristos /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof 97*63eb84d1Schristos values. */ 98*63eb84d1Schristos # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) 99*63eb84d1Schristos #else 100*63eb84d1Schristos # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) 101*63eb84d1Schristos #endif 102*63eb84d1Schristos 103*63eb84d1Schristos enum 104*63eb84d1Schristos { 105*63eb84d1Schristos /* The desired alignment of memory allocations is the maximum alignment 106*63eb84d1Schristos among all elementary types. */ 107*63eb84d1Schristos sa_alignment_long = sa_alignof (long), 108*63eb84d1Schristos sa_alignment_double = sa_alignof (double), 109*63eb84d1Schristos #ifdef HAVE_LONG_LONG_INT 110*63eb84d1Schristos sa_alignment_longlong = sa_alignof (long long), 111*63eb84d1Schristos #endif 112*63eb84d1Schristos #ifdef HAVE_LONG_DOUBLE 113*63eb84d1Schristos sa_alignment_longdouble = sa_alignof (long double), 114*63eb84d1Schristos #endif 115*63eb84d1Schristos sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1) 116*63eb84d1Schristos #ifdef HAVE_LONG_LONG_INT 117*63eb84d1Schristos | (sa_alignment_longlong - 1) 118*63eb84d1Schristos #endif 119*63eb84d1Schristos #ifdef HAVE_LONG_DOUBLE 120*63eb84d1Schristos | (sa_alignment_longdouble - 1) 121*63eb84d1Schristos #endif 122*63eb84d1Schristos ) + 1, 123*63eb84d1Schristos /* The increment that guarantees room for a magic word must be >= sizeof (int) 124*63eb84d1Schristos and a multiple of sa_alignment_max. */ 125*63eb84d1Schristos sa_increment = ((sizeof (int) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max 126*63eb84d1Schristos }; 127*63eb84d1Schristos 128*63eb84d1Schristos #endif /* _ALLOCSA_H */ 129