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/*
* test-sgen-qsort.c: Our own bzero/memmove.
*
* Copyright (C) 2013 Xamarin Inc
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License 2.0 as published by the Free Software Foundation;
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License 2.0 along with this library; if not, write to the Free
* Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
/*
* SGen cannot deal with invalid pointers on the heap or in registered roots. Sometimes we
* need to copy or zero out memory in code that might be interrupted by collections. To
* guarantee that those operations will not result in invalid pointers, we must do it
* word-atomically.
*
* libc's bzero() and memcpy()/memmove() functions do not guarantee word-atomicity, even in
* cases where one would assume so. For instance, some implementations (like Darwin's on
* x86) have variants of memcpy() using vector instructions. Those may copy bytewise for
* the region preceding the first vector-aligned address. That region could be
* word-aligned, but it would still be copied byte-wise.
*
* All our memory writes here are to "volatile" locations. This is so that C compilers
* don't "optimize" our code back to calls to bzero()/memmove(). LLVM, specifically, will
* do that.
*/
#include <config.h>
#include "metadata/gc-internal.h"
#define ptr_mask ((sizeof (void*) - 1))
#define _toi(ptr) ((size_t)ptr)
#define unaligned_bytes(ptr) (_toi(ptr) & ptr_mask)
#define align_down(ptr) ((void*)(_toi(ptr) & ~ptr_mask))
#define align_up(ptr) ((void*) ((_toi(ptr) + ptr_mask) & ~ptr_mask))
#if SIZEOF_VOID_P == 4
#define bytes_to_words(n) ((size_t)(n) >> 2)
#elif SIZEOF_VOID_P == 8
#define bytes_to_words(n) ((size_t)(n) >> 3)
#else
#error We only support 32 and 64 bit architectures.
#endif
#define BZERO_WORDS(dest,words) do { \
void * volatile *__d = (void* volatile*)(dest); \
int __n = (words); \
int __i; \
for (__i = 0; __i < __n; ++__i) \
__d [__i] = NULL; \
} while (0)
/**
* mono_gc_bzero_aligned:
* @dest: address to start to clear
* @size: size of the region to clear
*
* Zero @size bytes starting at @dest.
* The address of @dest MUST be aligned to word boundaries
*
* FIXME borrow faster code from some BSD libc or bionic
*/
void
mono_gc_bzero_aligned (void *dest, size_t size)
{
volatile char *d = (char*)dest;
size_t tail_bytes, word_bytes;
g_assert (unaligned_bytes (dest) == 0);
/* copy all words with memmove */
word_bytes = (size_t)align_down (size);
switch (word_bytes) {
case sizeof (void*) * 1:
BZERO_WORDS (d, 1);
break;
case sizeof (void*) * 2:
BZERO_WORDS (d, 2);
break;
case sizeof (void*) * 3:
BZERO_WORDS (d, 3);
break;
case sizeof (void*) * 4:
BZERO_WORDS (d, 4);
break;
default:
BZERO_WORDS (d, bytes_to_words (word_bytes));
}
tail_bytes = unaligned_bytes (size);
if (tail_bytes) {
d += word_bytes;
do {
*d++ = 0;
} while (--tail_bytes);
}
}
/**
* mono_gc_bzero_atomic:
* @dest: address to start to clear
* @size: size of the region to clear
*
* Zero @size bytes starting at @dest.
*
* Use this to zero memory without word tearing when dest is aligned.
*/
void
mono_gc_bzero_atomic (void *dest, size_t size)
{
if (unaligned_bytes (dest))
memset (dest, 0, size);
else
mono_gc_bzero_aligned (dest, size);
}
#define MEMMOVE_WORDS_UPWARD(dest,src,words) do { \
void * volatile *__d = (void* volatile*)(dest); \
void **__s = (void**)(src); \
int __n = (int)(words); \
int __i; \
for (__i = 0; __i < __n; ++__i) \
__d [__i] = __s [__i]; \
} while (0)
#define MEMMOVE_WORDS_DOWNWARD(dest,src,words) do { \
void * volatile *__d = (void* volatile*)(dest); \
void **__s = (void**)(src); \
int __n = (int)(words); \
int __i; \
for (__i = __n - 1; __i >= 0; --__i) \
__d [__i] = __s [__i]; \
} while (0)
/**
* mono_gc_memmove_aligned:
* @dest: destination of the move
* @src: source
* @size: size of the block to move
*
* Move @size bytes from @src to @dest.
*
* Use this to copy memory without word tearing when both pointers are aligned
*/void
mono_gc_memmove_aligned (void *dest, const void *src, size_t size)
{
g_assert (unaligned_bytes (dest) == 0);
g_assert (unaligned_bytes (src) == 0);
/*
If we're copying less than a word we don't need to worry about word tearing
so we bailout to memmove early.
*/
if (size < sizeof(void*)) {
memmove (dest, src, size);
return;
}
/*
* A bit of explanation on why we align only dest before doing word copies.
* Pointers to managed objects must always be stored in word aligned addresses, so
* even if dest is misaligned, src will be by the same amount - this ensure proper atomicity of reads.
*
* We don't need to case when source and destination have different alignments since we only do word stores
* using memmove, which must handle it.
*/
if (dest > src && ((size_t)((char*)dest - (char*)src) < size)) { /*backward copy*/
volatile char *p = (char*)dest + size;
char *s = (char*)src + size;
char *start = (char*)dest;
char *align_end = MAX((char*)dest, (char*)align_down (p));
char *word_start;
size_t bytes_to_memmove;
while (p > align_end)
*--p = *--s;
word_start = align_up (start);
bytes_to_memmove = p - word_start;
p -= bytes_to_memmove;
s -= bytes_to_memmove;
MEMMOVE_WORDS_DOWNWARD (p, s, bytes_to_words (bytes_to_memmove));
} else {
volatile char *d = (char*)dest;
const char *s = (const char*)src;
size_t tail_bytes;
/* copy all words with memmove */
MEMMOVE_WORDS_UPWARD (d, s, bytes_to_words (align_down (size)));
tail_bytes = unaligned_bytes (size);
if (tail_bytes) {
d += (size_t)align_down (size);
s += (size_t)align_down (size);
do {
*d++ = *s++;
} while (--tail_bytes);
}
}
}
/**
* mono_gc_memmove_atomic:
* @dest: destination of the move
* @src: source
* @size: size of the block to move
*
* Move @size bytes from @src to @dest.
*
* Use this to copy memory without word tearing when both pointers are aligned
*/
void
mono_gc_memmove_atomic (void *dest, const void *src, size_t size)
{
if (unaligned_bytes (_toi (dest) | _toi (src)))
memmove (dest, src, size);
else
mono_gc_memmove_aligned (dest, src, size);
}
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