embedaddon/libiconv/srclib/malloca.c - diff

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Diff for /embedaddon/libiconv/srclib/malloca.c between versions 1.1 and 1.1.1.3

version 1.1, 2012/02/21 22:57:48	version 1.1.1.3, 2021/03/17 13:38:46
Line 1	Line 1
/* Safe automatic memory allocation.	/* Safe automatic memory allocation.
Copyright (C) 2003, 2006-2007 Free Software Foundation, Inc.	Copyright (C) 2003, 2006-2007, 2009-2019 Free Software Foundation, Inc.
Written by Bruno Haible <bruno@clisp.org>, 2003.	Written by Bruno Haible <bruno@clisp.org>, 2003, 2018.

This program is free software; you can redistribute it and/or modify	This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by	it under the terms of the GNU General Public License as published by
Line 13	Line 13
GNU General Public License for more details.	GNU General Public License for more details.

You should have received a copy of the GNU General Public License	You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software Foundation,	along with this program; if not, see <https://www.gnu.org/licenses/>. */
Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */

	#define _GL_USE_STDLIB_ALLOC 1
#include <config.h>	#include <config.h>

/* Specification. */	/* Specification. */
#include "malloca.h"	#include "malloca.h"

	#include "verify.h"

/* The speed critical point in this file is freea() applied to an alloca()	/* The speed critical point in this file is freea() applied to an alloca()
result: it must be fast, to match the speed of alloca(). The speed of	result: it must be fast, to match the speed of alloca(). The speed of
mmalloca() and freea() in the other case are not critical, because they	mmalloca() and freea() in the other case are not critical, because they
are only invoked for big memory sizes. */	are only invoked for big memory sizes.
	Here we use a bit in the address as an indicator, an idea by Ondřej Bílka.
	malloca() can return three types of pointers:
	- Pointers ≡ 0 mod 2*sa_alignment_max come from stack allocation.
	- Pointers ≡ sa_alignment_max mod 2*sa_alignment_max come from heap
	allocation.
	- NULL comes from a failed heap allocation. */

#if HAVE_ALLOCA	/* Type for holding very small pointer differences. */
	typedef unsigned char small_t;
	/* Verify that it is wide enough. */
	verify (2 * sa_alignment_max - 1 <= (small_t) -1);

/* Store the mmalloca() results in a hash table. This is needed to reliably
distinguish a mmalloca() result and an alloca() result.

Although it is possible that the same pointer is returned by alloca() and
by mmalloca() at different times in the same application, it does not lead
to a bug in freea(), because:
- Before a pointer returned by alloca() can point into malloc()ed memory,
the function must return, and once this has happened the programmer must
not call freea() on it anyway.
- Before a pointer returned by mmalloca() can point into the stack, it
must be freed. The only function that can free it is freea(), and
when freea() frees it, it also removes it from the hash table. */

#define MAGIC_NUMBER 0x1415fb4a
#define MAGIC_SIZE sizeof (int)
/* This is how the header info would look like without any alignment
considerations. */
struct preliminary_header { void *next; char room[MAGIC_SIZE]; };
/* But the header's size must be a multiple of sa_alignment_max. */
#define HEADER_SIZE \
(((sizeof (struct preliminary_header) + sa_alignment_max - 1) / sa_alignment_max) * sa_alignment_max)
struct header { void *next; char room[HEADER_SIZE - sizeof (struct preliminary_header) + MAGIC_SIZE]; };
/* Verify that HEADER_SIZE == sizeof (struct header). */
typedef int verify1[2 * (HEADER_SIZE == sizeof (struct header)) - 1];
/* We make the hash table quite big, so that during lookups the probability
of empty hash buckets is quite high. There is no need to make the hash
table resizable, because when the hash table gets filled so much that the
lookup becomes slow, it means that the application has memory leaks. */
#define HASH_TABLE_SIZE 257
static void * mmalloca_results[HASH_TABLE_SIZE];

#endif

void *	void *
mmalloca (size_t n)	mmalloca (size_t n)
{	{
#if HAVE_ALLOCA	#if HAVE_ALLOCA
/* Allocate one more word, that serves as an indicator for malloc()ed	/* Allocate one more word, used to determine the address to pass to freea(),
memory, so that freea() of an alloca() result is fast. */	and room for the alignment ≡ sa_alignment_max mod 2sa_alignment_max. /
size_t nplus = n + HEADER_SIZE;	size_t nplus = n + sizeof (small_t) + 2 * sa_alignment_max - 1;

if (nplus >= n)	if (nplus >= n)
{	{
char p = (char ) malloc (nplus);	char mem = (char ) malloc (nplus);

if (p != NULL)	if (mem != NULL)
{	{
size_t slot;	char *p =
	(char *)((((uintptr_t)mem + sizeof (small_t) + sa_alignment_max - 1)
p += HEADER_SIZE;	& ~(uintptr_t)(2 * sa_alignment_max - 1))
	+ sa_alignment_max);
/* Put a magic number into the indicator word. */	/* Here p >= mem + sizeof (small_t),
((int *) p)[-1] = MAGIC_NUMBER;	and p <= mem + sizeof (small_t) + 2 * sa_alignment_max - 1
	hence p + n <= mem + nplus.
/* Enter p into the hash table. */	So, the memory range [p, p+n) lies in the allocated memory range
slot = (unsigned long) p % HASH_TABLE_SIZE;	[mem, mem + nplus). */
((struct header *) (p - HEADER_SIZE))->next = mmalloca_results[slot];	((small_t *) p)[-1] = p - mem;
mmalloca_results[slot] = p;	/* p ≡ sa_alignment_max mod 2sa_alignment_max. /
	return p;
return p;	}
}
}	}
/* Out of memory. */	/* Out of memory. */
return NULL;	return NULL;
Line 105 mmalloca (size_t n)	Line 82 mmalloca (size_t n)
void	void
freea (void *p)	freea (void *p)
{	{
/* mmalloca() may have returned NULL. */	/* Check argument. */
if (p != NULL)	if ((uintptr_t) p & (sa_alignment_max - 1))
{	{
/* Attempt to quickly distinguish the mmalloca() result - which has	/* p was not the result of a malloca() call. Invalid argument. */
a magic indicator word - and the alloca() result - which has an	abort ();
uninitialized indicator word. It is for this test that sa_increment
additional bytes are allocated in the alloca() case. */
if (((int *) p)[-1] == MAGIC_NUMBER)
{
/* Looks like a mmalloca() result. To see whether it really is one,
perform a lookup in the hash table. */
size_t slot = (unsigned long) p % HASH_TABLE_SIZE;
void **chain = &mmalloca_results[slot];
for (; *chain != NULL;)
{
if (*chain == p)
{
/* Found it. Remove it from the hash table and free it. */
char p_begin = (char ) p - HEADER_SIZE;
chain = ((struct header ) p_begin)->next;
free (p_begin);
return;
}
chain = &((struct header ) ((char ) *chain - HEADER_SIZE))->next;
}
}
/* At this point, we know it was not a mmalloca() result. */
}	}
	/* Determine whether p was a non-NULL pointer returned by mmalloca(). */
	if ((uintptr_t) p & sa_alignment_max)
	{
	void mem = (char ) p - ((small_t *) p)[-1];
	free (mem);
	}
}	}
#endif	#endif

	/*
	* Hey Emacs!
	* Local Variables:
	* coding: utf-8
	* End:
	*/

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