1 #include "asan_impl.h"
2 #include "libc.h"
3 #include <stdint.h>
4 #include <string.h>
5
memset(void * dest,int c,size_t n)6 NO_ASAN void* memset(void* dest, int c, size_t n) {
7 unsigned char* s = dest;
8 size_t k;
9
10 /* Fill head and tail with minimal branching. Each
11 * conditional ensures that all the subsequently used
12 * offsets are well-defined and in the dest region. */
13
14 if (!n)
15 return dest;
16 s[0] = s[n - 1] = c;
17 if (n <= 2)
18 return dest;
19 s[1] = s[n - 2] = c;
20 s[2] = s[n - 3] = c;
21 if (n <= 6)
22 return dest;
23 s[3] = s[n - 4] = c;
24 if (n <= 8)
25 return dest;
26
27 /* Advance pointer to align it at a 4-byte boundary,
28 * and truncate n to a multiple of 4. The previous code
29 * already took care of any head/tail that get cut off
30 * by the alignment. */
31
32 k = -(uintptr_t)s & 3;
33 s += k;
34 n -= k;
35 n &= -4;
36
37 #ifdef __GNUC__
38 typedef uint32_t __attribute__((__may_alias__)) u32;
39 typedef uint64_t __attribute__((__may_alias__)) u64;
40
41 u32 c32 = ((u32)-1) / 255 * (unsigned char)c;
42
43 /* In preparation to copy 32 bytes at a time, aligned on
44 * an 8-byte bounary, fill head/tail up to 28 bytes each.
45 * As in the initial byte-based head/tail fill, each
46 * conditional below ensures that the subsequent offsets
47 * are valid (e.g. !(n<=24) implies n>=28). */
48
49 *(u32*)(s + 0) = c32;
50 *(u32*)(s + n - 4) = c32;
51 if (n <= 8)
52 return dest;
53 *(u32*)(s + 4) = c32;
54 *(u32*)(s + 8) = c32;
55 *(u32*)(s + n - 12) = c32;
56 *(u32*)(s + n - 8) = c32;
57 if (n <= 24)
58 return dest;
59 *(u32*)(s + 12) = c32;
60 *(u32*)(s + 16) = c32;
61 *(u32*)(s + 20) = c32;
62 *(u32*)(s + 24) = c32;
63 *(u32*)(s + n - 28) = c32;
64 *(u32*)(s + n - 24) = c32;
65 *(u32*)(s + n - 20) = c32;
66 *(u32*)(s + n - 16) = c32;
67
68 /* Align to a multiple of 8 so we can fill 64 bits at a time,
69 * and avoid writing the same bytes twice as much as is
70 * practical without introducing additional branching. */
71
72 k = 24 + ((uintptr_t)s & 4);
73 s += k;
74 n -= k;
75
76 /* If this loop is reached, 28 tail bytes have already been
77 * filled, so any remainder when n drops below 32 can be
78 * safely ignored. */
79
80 u64 c64 = c32 | ((u64)c32 << 32);
81 for (; n >= 32; n -= 32, s += 32) {
82 *(u64*)(s + 0) = c64;
83 *(u64*)(s + 8) = c64;
84 *(u64*)(s + 16) = c64;
85 *(u64*)(s + 24) = c64;
86 }
87 #else
88 /* Pure C fallback with no aliasing violations. */
89 for (; n; n--, s++)
90 *s = c;
91 #endif
92
93 return dest;
94 }
95
96 __typeof(memset) __unsanitized_memset __attribute__((alias("memset")));
97 __asan_weak_alias(memset)
98