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95 lines
3.6 KiB
C
95 lines
3.6 KiB
C
/* Internal declarations for malloc, for use within libc.
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Copyright (C) 2016-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify 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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The GNU C Library 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 GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, see <http://www.gnu.org/licenses/>. */
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#ifndef _MALLOC_INTERNAL_H
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#define _MALLOC_INTERNAL_H
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#include <malloc-machine.h>
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#include <malloc-sysdep.h>
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/* INTERNAL_SIZE_T is the word-size used for internal bookkeeping of
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chunk sizes.
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The default version is the same as size_t.
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While not strictly necessary, it is best to define this as an
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unsigned type, even if size_t is a signed type. This may avoid some
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artificial size limitations on some systems.
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On a 64-bit machine, you may be able to reduce malloc overhead by
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defining INTERNAL_SIZE_T to be a 32 bit `unsigned int' at the
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expense of not being able to handle more than 2^32 of malloced
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space. If this limitation is acceptable, you are encouraged to set
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this unless you are on a platform requiring 16byte alignments. In
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this case the alignment requirements turn out to negate any
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potential advantages of decreasing size_t word size.
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Implementors: Beware of the possible combinations of:
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- INTERNAL_SIZE_T might be signed or unsigned, might be 32 or 64 bits,
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and might be the same width as int or as long
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- size_t might have different width and signedness as INTERNAL_SIZE_T
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- int and long might be 32 or 64 bits, and might be the same width
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To deal with this, most comparisons and difference computations
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among INTERNAL_SIZE_Ts should cast them to unsigned long, being
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aware of the fact that casting an unsigned int to a wider long does
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not sign-extend. (This also makes checking for negative numbers
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awkward.) Some of these casts result in harmless compiler warnings
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on some systems. */
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#ifndef INTERNAL_SIZE_T
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# define INTERNAL_SIZE_T size_t
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#endif
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/* The corresponding word size. */
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#define SIZE_SZ (sizeof (INTERNAL_SIZE_T))
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/* The corresponding bit mask value. */
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#define MALLOC_ALIGN_MASK (MALLOC_ALIGNMENT - 1)
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/* Called in the parent process before a fork. */
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void __malloc_fork_lock_parent (void) attribute_hidden;
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/* Called in the parent process after a fork. */
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void __malloc_fork_unlock_parent (void) attribute_hidden;
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/* Called in the child process after a fork. */
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void __malloc_fork_unlock_child (void) attribute_hidden;
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/* Set *RESULT to LEFT * RIGHT. Return true if the multiplication
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overflowed. */
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static inline bool
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check_mul_overflow_size_t (size_t left, size_t right, size_t *result)
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{
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#if __GNUC__ >= 5
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return __builtin_mul_overflow (left, right, result);
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#else
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/* size_t is unsigned so the behavior on overflow is defined. */
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*result = left * right;
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size_t half_size_t = ((size_t) 1) << (8 * sizeof (size_t) / 2);
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if (__glibc_unlikely ((left | right) >= half_size_t))
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{
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if (__glibc_unlikely (right != 0 && *result / right != left))
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return true;
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}
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return false;
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#endif
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}
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#endif /* _MALLOC_INTERNAL_H */
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