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
| | #include <limits.h>
#include <stdint.h>
#include <errno.h>
#include <sys/mman.h>
#include "libc.h"
#include "syscall.h"
/* This function returns true if the interval [old,new]
* intersects the 'len'-sized interval below &libc.auxv
* (interpreted as the main-thread stack) or below &b
* (the current stack). It is used to defend against
* buggy brk implementations that can cross the stack. */
static int traverses_stack_p(uintptr_t old, uintptr_t new)
{
#if !SAFE_STACK
const uintptr_t len = 8<<20;
uintptr_t a, b;
b = (uintptr_t)libc.auxv;
a = b > len ? b-len : 0;
if (new>a && old<b) return 1;
b = (uintptr_t)&b;
a = b > len ? b-len : 0;
if (new>a && old<b) return 1;
#endif
return 0;
}
void *__mmap(void *, size_t, int, int, int, off_t);
/* Expand the heap in-place if brk can be used, or otherwise via mmap,
* using an exponential lower bound on growth by mmap to make
* fragmentation asymptotically irrelevant. The size argument is both
* an input and an output, since the caller needs to know the size
* allocated, which will be larger than requested due to page alignment
* and mmap minimum size rules. The caller is responsible for locking
* to prevent concurrent calls. */
void *__expand_heap(size_t *pn)
{
static uintptr_t brk;
static unsigned mmap_step;
size_t n = *pn;
if (n > SIZE_MAX/2 - PAGE_SIZE) {
errno = ENOMEM;
return 0;
}
n += -n & PAGE_SIZE-1;
if (!brk) {
brk = __syscall(SYS_brk, 0);
brk += -brk & PAGE_SIZE-1;
}
if (n < SIZE_MAX-brk && !traverses_stack_p(brk, brk+n)
&& __syscall(SYS_brk, brk+n)==brk+n) {
*pn = n;
brk += n;
return (void *)(brk-n);
}
size_t min = (size_t)PAGE_SIZE << mmap_step/2;
if (n < min) n = min;
void *area = __mmap(0, n, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
if (area == MAP_FAILED) return 0;
*pn = n;
mmap_step++;
return area;
}
|