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msvcrt: Fix _Aligned_offset_realloc (move correct block of memory); add a comment to explain why.

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This commit is contained in:
Lionel Debroux 2007-11-28 11:47:18 +01:00 committed by Alexandre Julliard
parent 1aff3528cf
commit 3e9fbd89d2
1 changed files with 50 additions and 6 deletions
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56
dlls/msvcrt/heap.c
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@ -396,7 +396,7 @@ void * CDECL _aligned_offset_realloc(void *memblock, MSVCRT_size_t size,
MSVCRT_size_t alignment, MSVCRT_size_t offset)
{
void * temp, **saved;
MSVCRT_size_t old_padding, new_padding;
MSVCRT_size_t old_padding, new_padding, old_size;
TRACE("(%p, %u, %u, %u)\n", memblock, size, alignment, offset);
if (!memblock)
@ -434,7 +434,22 @@ void * CDECL _aligned_offset_realloc(void *memblock, MSVCRT_size_t size,
return NULL;
}
old_padding = (char *)*saved - (char *)memblock;
old_padding = (char *)memblock - (char *)*saved;
/* Get previous size of block */
old_size = _msize(*saved);
if (old_size == -1)
{
/* It seems this function was called with an invalid pointer. Bail out. */
return NULL;
}
/* Adjust old_size to get amount of actual data in old block. */
old_size -= old_padding;
if (old_size < 0)
{
/* Shouldn't happen. Something's weird, so bail out. */
return NULL;
}
temp = MSVCRT_realloc(*saved, size + alignment + sizeof(void *));
@ -448,11 +463,40 @@ void * CDECL _aligned_offset_realloc(void *memblock, MSVCRT_size_t size,
/* so it can be found later to free. */
saved = SAVED_PTR(memblock);
/* a new start address may require different padding to get the */
/* proper alignment */
new_padding = (char *)temp - (char *)memblock;
new_padding = (char *)memblock - (char *)temp;
/*
Memory layout of old block is as follows:
+-------+---------------------+-+--------------------------+-----------+
| ... | "old_padding" bytes | | ... "old_size" bytes ... | ... |
+-------+---------------------+-+--------------------------+-----------+
^ ^ ^
| | |
*saved saved memblock
Memory layout of new block is as follows:
+-------+-----------------------------+-+----------------------+-------+
| ... | "new_padding" bytes | | ... "size" bytes ... | ... |
+-------+-----------------------------+-+----------------------+-------+
^ ^ ^
| | |
temp saved memblock
However, in the new block, actual data is still written as follows
(because it was copied by MSVCRT_realloc):
+-------+---------------------+--------------------------------+-------+
| ... | "old_padding" bytes | ... "old_size" bytes ... | ... |
+-------+---------------------+--------------------------------+-------+
^ ^ ^
| | |
temp saved memblock
Therefore, min(old_size,size) bytes of actual data have to be moved
from the offset they were at in the old block (temp + old_padding),
to the offset they have to be in the new block (temp + new_padding == memblock).
*/
if (new_padding != old_padding)
memmove((char *)memblock + old_padding, (char *)memblock + new_padding, size);
memmove((char *)memblock, (char *)temp + old_padding, (old_size < size) ? old_size : size);
*saved = temp;