1*56bb7041Schristos /* Safe automatic memory allocation. 2*56bb7041Schristos Copyright (C) 2003-2007, 2009-2020 Free Software Foundation, Inc. 3*56bb7041Schristos Written by Bruno Haible <bruno@clisp.org>, 2003. 4*56bb7041Schristos 5*56bb7041Schristos This program is free software; you can redistribute it and/or modify 6*56bb7041Schristos it under the terms of the GNU General Public License as published by 7*56bb7041Schristos the Free Software Foundation; either version 3, or (at your option) 8*56bb7041Schristos any later version. 9*56bb7041Schristos 10*56bb7041Schristos This program is distributed in the hope that it will be useful, 11*56bb7041Schristos but WITHOUT ANY WARRANTY; without even the implied warranty of 12*56bb7041Schristos MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 13*56bb7041Schristos GNU General Public License for more details. 14*56bb7041Schristos 15*56bb7041Schristos You should have received a copy of the GNU General Public License 16*56bb7041Schristos along with this program; if not, see <https://www.gnu.org/licenses/>. */ 17*56bb7041Schristos 18*56bb7041Schristos #ifndef _MALLOCA_H 19*56bb7041Schristos #define _MALLOCA_H 20*56bb7041Schristos 21*56bb7041Schristos #include <alloca.h> 22*56bb7041Schristos #include <stddef.h> 23*56bb7041Schristos #include <stdlib.h> 24*56bb7041Schristos #include <stdint.h> 25*56bb7041Schristos 26*56bb7041Schristos #include "xalloc-oversized.h" 27*56bb7041Schristos 28*56bb7041Schristos 29*56bb7041Schristos #ifdef __cplusplus 30*56bb7041Schristos extern "C" { 31*56bb7041Schristos #endif 32*56bb7041Schristos 33*56bb7041Schristos 34*56bb7041Schristos /* safe_alloca(N) is equivalent to alloca(N) when it is safe to call 35*56bb7041Schristos alloca(N); otherwise it returns NULL. It either returns N bytes of 36*56bb7041Schristos memory allocated on the stack, that lasts until the function returns, 37*56bb7041Schristos or NULL. 38*56bb7041Schristos Use of safe_alloca should be avoided: 39*56bb7041Schristos - inside arguments of function calls - undefined behaviour, 40*56bb7041Schristos - in inline functions - the allocation may actually last until the 41*56bb7041Schristos calling function returns. 42*56bb7041Schristos */ 43*56bb7041Schristos #if HAVE_ALLOCA 44*56bb7041Schristos /* The OS usually guarantees only one guard page at the bottom of the stack, 45*56bb7041Schristos and a page size can be as small as 4096 bytes. So we cannot safely 46*56bb7041Schristos allocate anything larger than 4096 bytes. Also care for the possibility 47*56bb7041Schristos of a few compiler-allocated temporary stack slots. 48*56bb7041Schristos This must be a macro, not a function. */ 49*56bb7041Schristos # define safe_alloca(N) ((N) < 4032 ? alloca (N) : NULL) 50*56bb7041Schristos #else 51*56bb7041Schristos # define safe_alloca(N) ((void) (N), NULL) 52*56bb7041Schristos #endif 53*56bb7041Schristos 54*56bb7041Schristos /* malloca(N) is a safe variant of alloca(N). It allocates N bytes of 55*56bb7041Schristos memory allocated on the stack, that must be freed using freea() before 56*56bb7041Schristos the function returns. Upon failure, it returns NULL. */ 57*56bb7041Schristos #if HAVE_ALLOCA 58*56bb7041Schristos # define malloca(N) \ 59*56bb7041Schristos ((N) < 4032 - (2 * sa_alignment_max - 1) \ 60*56bb7041Schristos ? (void *) (((uintptr_t) (char *) alloca ((N) + 2 * sa_alignment_max - 1) \ 61*56bb7041Schristos + (2 * sa_alignment_max - 1)) \ 62*56bb7041Schristos & ~(uintptr_t)(2 * sa_alignment_max - 1)) \ 63*56bb7041Schristos : mmalloca (N)) 64*56bb7041Schristos #else 65*56bb7041Schristos # define malloca(N) \ 66*56bb7041Schristos mmalloca (N) 67*56bb7041Schristos #endif 68*56bb7041Schristos extern void * mmalloca (size_t n); 69*56bb7041Schristos 70*56bb7041Schristos /* Free a block of memory allocated through malloca(). */ 71*56bb7041Schristos #if HAVE_ALLOCA 72*56bb7041Schristos extern void freea (void *p); 73*56bb7041Schristos #else 74*56bb7041Schristos # define freea free 75*56bb7041Schristos #endif 76*56bb7041Schristos 77*56bb7041Schristos /* nmalloca(N,S) is an overflow-safe variant of malloca (N * S). 78*56bb7041Schristos It allocates an array of N objects, each with S bytes of memory, 79*56bb7041Schristos on the stack. S must be positive and N must be nonnegative. 80*56bb7041Schristos The array must be freed using freea() before the function returns. */ 81*56bb7041Schristos #define nmalloca(n, s) (xalloc_oversized (n, s) ? NULL : malloca ((n) * (s))) 82*56bb7041Schristos 83*56bb7041Schristos 84*56bb7041Schristos #ifdef __cplusplus 85*56bb7041Schristos } 86*56bb7041Schristos #endif 87*56bb7041Schristos 88*56bb7041Schristos 89*56bb7041Schristos /* ------------------- Auxiliary, non-public definitions ------------------- */ 90*56bb7041Schristos 91*56bb7041Schristos /* Determine the alignment of a type at compile time. */ 92*56bb7041Schristos #if defined __GNUC__ || defined __IBM__ALIGNOF__ 93*56bb7041Schristos # define sa_alignof __alignof__ 94*56bb7041Schristos #elif defined __cplusplus 95*56bb7041Schristos template <class type> struct sa_alignof_helper { char __slot1; type __slot2; }; 96*56bb7041Schristos # define sa_alignof(type) offsetof (sa_alignof_helper<type>, __slot2) 97*56bb7041Schristos #elif defined __hpux 98*56bb7041Schristos /* Work around a HP-UX 10.20 cc bug with enums constants defined as offsetof 99*56bb7041Schristos values. */ 100*56bb7041Schristos # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) 101*56bb7041Schristos #elif defined _AIX 102*56bb7041Schristos /* Work around an AIX 3.2.5 xlc bug with enums constants defined as offsetof 103*56bb7041Schristos values. */ 104*56bb7041Schristos # define sa_alignof(type) (sizeof (type) <= 4 ? 4 : 8) 105*56bb7041Schristos #else 106*56bb7041Schristos # define sa_alignof(type) offsetof (struct { char __slot1; type __slot2; }, __slot2) 107*56bb7041Schristos #endif 108*56bb7041Schristos 109*56bb7041Schristos enum 110*56bb7041Schristos { 111*56bb7041Schristos /* The desired alignment of memory allocations is the maximum alignment 112*56bb7041Schristos among all elementary types. */ 113*56bb7041Schristos sa_alignment_long = sa_alignof (long), 114*56bb7041Schristos sa_alignment_double = sa_alignof (double), 115*56bb7041Schristos sa_alignment_longlong = sa_alignof (long long), 116*56bb7041Schristos sa_alignment_longdouble = sa_alignof (long double), 117*56bb7041Schristos sa_alignment_max = ((sa_alignment_long - 1) | (sa_alignment_double - 1) 118*56bb7041Schristos | (sa_alignment_longlong - 1) 119*56bb7041Schristos | (sa_alignment_longdouble - 1) 120*56bb7041Schristos ) + 1 121*56bb7041Schristos }; 122*56bb7041Schristos 123*56bb7041Schristos #endif /* _MALLOCA_H */ 124