114 lines
3.7 KiB
C
114 lines
3.7 KiB
C
/* Safe automatic memory allocation.
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Copyright (C) 2003, 2006-2007, 2009-2022 Free Software Foundation, Inc.
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Written by Bruno Haible <bruno@clisp.org>, 2003, 2018.
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This file is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as
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published by the Free Software Foundation; either version 2.1 of the
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License, or (at your option) any later version.
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This file is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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#define _GL_USE_STDLIB_ALLOC 1
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#include <config.h>
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/* Specification. */
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#include "malloca.h"
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#include "idx.h"
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#include "intprops.h"
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#include "verify.h"
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/* The speed critical point in this file is freea() applied to an alloca()
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result: it must be fast, to match the speed of alloca(). The speed of
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mmalloca() and freea() in the other case are not critical, because they
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are only invoked for big memory sizes.
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Here we use a bit in the address as an indicator, an idea by Ondřej Bílka.
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malloca() can return three types of pointers:
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- Pointers ≡ 0 mod 2*sa_alignment_max come from stack allocation.
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- Pointers ≡ sa_alignment_max mod 2*sa_alignment_max come from heap
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allocation.
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- NULL comes from a failed heap allocation. */
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/* Type for holding very small pointer differences. */
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typedef unsigned char small_t;
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/* Verify that it is wide enough. */
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verify (2 * sa_alignment_max - 1 <= (small_t) -1);
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void *
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mmalloca (size_t n)
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{
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#if HAVE_ALLOCA
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/* Allocate one more word, used to determine the address to pass to freea(),
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and room for the alignment ≡ sa_alignment_max mod 2*sa_alignment_max. */
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uintptr_t alignment2_mask = 2 * sa_alignment_max - 1;
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int plus = sizeof (small_t) + alignment2_mask;
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idx_t nplus;
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if (!INT_ADD_WRAPV (n, plus, &nplus) && !xalloc_oversized (nplus, 1))
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{
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char *mem = (char *) malloc (nplus);
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if (mem != NULL)
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{
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uintptr_t umem = (uintptr_t)mem, umemplus;
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/* The INT_ADD_WRAPV avoids signed integer overflow on
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theoretical platforms where UINTPTR_MAX <= INT_MAX. */
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INT_ADD_WRAPV (umem, sizeof (small_t) + sa_alignment_max - 1,
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&umemplus);
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idx_t offset = ((umemplus & ~alignment2_mask)
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+ sa_alignment_max - umem);
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void *vp = mem + offset;
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small_t *p = vp;
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/* Here p >= mem + sizeof (small_t),
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and p <= mem + sizeof (small_t) + 2 * sa_alignment_max - 1
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hence p + n <= mem + nplus.
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So, the memory range [p, p+n) lies in the allocated memory range
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[mem, mem + nplus). */
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p[-1] = offset;
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/* p ≡ sa_alignment_max mod 2*sa_alignment_max. */
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return p;
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}
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}
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/* Out of memory. */
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return NULL;
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#else
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# if !MALLOC_0_IS_NONNULL
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if (n == 0)
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n = 1;
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# endif
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return malloc (n);
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#endif
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}
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#if HAVE_ALLOCA
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void
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freea (void *p)
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{
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/* Check argument. */
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if ((uintptr_t) p & (sa_alignment_max - 1))
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{
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/* p was not the result of a malloca() call. Invalid argument. */
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abort ();
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}
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/* Determine whether p was a non-NULL pointer returned by mmalloca(). */
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if ((uintptr_t) p & sa_alignment_max)
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{
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void *mem = (char *) p - ((small_t *) p)[-1];
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free (mem);
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}
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}
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#endif
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/*
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* Hey Emacs!
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* Local Variables:
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* coding: utf-8
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* End:
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*/
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