1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
|
/*-------------------------------------------------------------------------
*
* memdebug.c
* Declarations used in memory context implementations, not part of the
* public API of the memory management subsystem.
*
*
* Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/backend/utils/mmgr/memdebug.c
*
*
* About CLOBBER_FREED_MEMORY:
*
* If this symbol is defined, all freed memory is overwritten with 0x7F's.
* This is useful for catching places that reference already-freed memory.
*
* About MEMORY_CONTEXT_CHECKING:
*
* Since we usually round request sizes up to the next power of 2, there
* is often some unused space immediately after a requested data area.
* Thus, if someone makes the common error of writing past what they've
* requested, the problem is likely to go unnoticed ... until the day when
* there *isn't* any wasted space, perhaps because of different memory
* alignment on a new platform, or some other effect. To catch this sort
* of problem, the MEMORY_CONTEXT_CHECKING option stores 0x7E just beyond
* the requested space whenever the request is less than the actual chunk
* size, and verifies that the byte is undamaged when the chunk is freed.
*
*
* About USE_VALGRIND and Valgrind client requests:
*
* Valgrind provides "client request" macros that exchange information with
* the host Valgrind (if any). Under !USE_VALGRIND, memdebug.h stubs out
* currently-used macros.
*
* When running under Valgrind, we want a NOACCESS memory region both before
* and after the allocation. The chunk header is tempting as the preceding
* region, but mcxt.c expects to able to examine the standard chunk header
* fields. Therefore, we use, when available, the requested_size field and
* any subsequent padding. requested_size is made NOACCESS before returning
* a chunk pointer to a caller. However, to reduce client request traffic,
* it is kept DEFINED in chunks on the free list.
*
* The rounded-up capacity of the chunk usually acts as a post-allocation
* NOACCESS region. If the request consumes precisely the entire chunk,
* there is no such region; another chunk header may immediately follow. In
* that case, Valgrind will not detect access beyond the end of the chunk.
*
* See also the cooperating Valgrind client requests in mcxt.c.
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "utils/memdebug.h"
#ifdef RANDOMIZE_ALLOCATED_MEMORY
/*
* Fill a just-allocated piece of memory with "random" data. It's not really
* very random, just a repeating sequence with a length that's prime. What
* we mainly want out of it is to have a good probability that two palloc's
* of the same number of bytes start out containing different data.
*
* The region may be NOACCESS, so make it UNDEFINED first to avoid errors as
* we fill it. Filling the region makes it DEFINED, so make it UNDEFINED
* again afterward. Whether to finally make it UNDEFINED or NOACCESS is
* fairly arbitrary. UNDEFINED is more convenient for SlabRealloc(), and
* other callers have no preference.
*/
void
randomize_mem(char *ptr, size_t size)
{
static int save_ctr = 1;
size_t remaining = size;
int ctr;
ctr = save_ctr;
VALGRIND_MAKE_MEM_UNDEFINED(ptr, size);
while (remaining-- > 0)
{
*ptr++ = ctr;
if (++ctr > 251)
ctr = 1;
}
VALGRIND_MAKE_MEM_UNDEFINED(ptr - size, size);
save_ctr = ctr;
}
#endif /* RANDOMIZE_ALLOCATED_MEMORY */
|
