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(cALLOc): Correctly handle systems where sbrk doesn't clear the

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contents of memory that is reallocated after decrementing the break
value first.  Update comment about MORECORE_CLEARS, explaining the
meaning of the values it can be set to.
This commit is contained in:
Ulrich Drepper 1999-09-25 06:52:12 +00:00
parent d99ce53936
commit 4d73e0ed98
1 changed files with 19 additions and 5 deletions
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24
malloc/malloc.c
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@ -226,8 +226,12 @@
MORECORE_FAILURE (default: -1)
The value returned upon failure of MORECORE.
MORECORE_CLEARS (default 1)
True (1) if the routine mapped to MORECORE zeroes out memory (which
holds for sbrk).
The degree to which the routine mapped to MORECORE zeroes out
memory: never (0), only for newly allocated space (1) or always
(2). The distinction between (1) and (2) is necessary because on
some systems, if the application first decrements and then
increments the break value, the contents of the reallocated space
are unspecified.
DEFAULT_TRIM_THRESHOLD
DEFAULT_TOP_PAD
DEFAULT_MMAP_THRESHOLD
@ -861,11 +865,15 @@ Void_t *(*__morecore)() = __default_morecore;
#endif
static size_t __libc_pagesize;
#define MORECORE (*__morecore)
#define MORECORE_FAILURE 0
#ifndef MORECORE_CLEARS
#define MORECORE_CLEARS 1
#endif
static size_t __libc_pagesize;
#define mmap __mmap
#define munmap __munmap
#define mremap __mremap
@ -3596,10 +3604,16 @@ Void_t* cALLOc(n, elem_size) size_t n; size_t elem_size;
if(!ar_ptr)
return 0;
/* check if expand_top called, in which case don't need to clear */
/* Check if expand_top called, in which case there may be
no need to clear. */
#if MORECORE_CLEARS
oldtop = top(ar_ptr);
oldtopsize = chunksize(top(ar_ptr));
#if MORECORE_CLEARS < 2
/* Only newly allocated memory is guaranteed to be cleared. */
if (oldtopsize < sbrk_base + max_sbrked_mem - (char *)oldtop)
oldtopsize = (sbrk_base + max_sbrked_mem - (char *)oldtop);
#endif
#endif
p = chunk_alloc (ar_ptr, sz);