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
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
|
#if 0
# From:
# https://github.com/skeeto/w64devkit/blob/master/src/libmemory.c
#
# because Clang generates calls to these, even with -fno-builtin, it is
# necessary to provide our implementation when not linking to C library.
#
# memset, memcpy, memmove, and memcmp via x86 string instructions
# Execute this source with a shell to build libmemory.a.
# This is free and unencumbered software released into the public domain.
set -e
CFLAGS="-Os -fno-builtin -fno-asynchronous-unwind-tables -fno-ident"
objects=""
for func in memset memcpy memmove memcmp strlen; do
FUNC="$(echo $func | tr '[:lower:]' '[:upper:]')"
objects="$objects $func.o"
(set -x; ${CC:-cc} -c -D$FUNC -Wa,--no-pad-sections $CFLAGS -o $func.o $0)
done
rm -f "${DESTDIR}libmemory.a"
${AR:-ar} r "${DESTDIR}libmemory.a" $objects
rm $objects
exit 0
#endif
typedef __SIZE_TYPE__ size_t;
typedef __UINTPTR_TYPE__ uintptr_t;
#ifdef MEMSET
void *memset(void *dst, int c, size_t len)
{
void *r = dst;
asm volatile (
"rep stosb"
: "+D"(dst), "+c"(len)
: "a"(c)
: "memory"
);
return r;
}
#endif
#ifdef MEMCPY
void *memcpy(void *restrict dst, void *restrict src, size_t len)
{
void *r = dst;
asm volatile (
"rep movsb"
: "+D"(dst), "+S"(src), "+c"(len)
:
: "memory"
);
return r;
}
#endif
#ifdef MEMMOVE
void *memmove(void *dst, void *src, size_t len)
{
// Use uintptr_t to bypass pointer semantics:
// (1) comparing unrelated pointers
// (2) pointer arithmetic on null (i.e. gracefully handle null dst/src)
// (3) pointer overflow ("one-before-the-beginning" in reversed copy)
uintptr_t d = (uintptr_t)dst;
uintptr_t s = (uintptr_t)src;
if (d > s) {
d += len - 1;
s += len - 1;
asm ("std");
}
asm volatile (
"rep movsb; cld"
: "+D"(d), "+S"(s), "+c"(len)
:
: "memory"
);
return dst;
}
#endif
#ifdef MEMCMP
int memcmp(void *s1, void *s2, size_t len)
{
// CCa "after" == CF=0 && ZF=0
// CCb "before" == CF=1
int a, b;
asm volatile (
"xor %%eax, %%eax\n" // CF=0, ZF=1 (i.e. CCa = CCb = 0)
"repz cmpsb\n"
: "+D"(s1), "+S"(s2), "+c"(len), "=@cca"(a), "=@ccb"(b)
:
: "ax", "memory"
);
return b - a;
}
#endif
#ifdef STRLEN
size_t strlen(char *s)
{
size_t n = -1;
asm volatile (
"repne scasb"
: "+D"(s), "+c"(n)
: "a"(0)
: "memory"
);
return -n - 2;
}
#endif
#ifdef TEST
// $ sh libmemory.c
// $ cc -nostdlib -fno-builtin -DTEST -g3 -O -o test libmemory.c libmemory.a
// $ gdb -ex r -ex q ./test
#define assert(c) while (!(c)) __builtin_trap()
void *memset(void *, int, size_t);
int memcmp(void *, void *, size_t);
void *memcpy(void *restrict, void *restrict, size_t);
void *memmove(void *, void *, size_t);
size_t strlen(char *);
#if defined(__linux) && defined(__amd64)
asm (" .global _start\n"
"_start: call mainCRTStartup\n"
" mov %eax, %edi\n"
" mov $60, %eax\n"
" syscall\n");
#elif defined(__linux) && defined(__i386)
asm (" .global _start\n"
"_start: call mainCRTStartup\n"
" mov %eax, %ebx\n"
" mov $1, %eax\n"
" int $0x80\n");
#endif
int mainCRTStartup(void)
{
{
char buf[12] = "............";
memset(buf+4, 'x', 4);
assert(!memcmp(buf, "....xxxx....", 12));
memset(buf, 0, 12);
assert(!memcmp(buf, (char[12]){0}, 12));
memset(buf+8, 1, 0);
assert(!memcmp(buf, (char[12]){0}, 12));
}
{
char buf[7] = "abcdefg";
memcpy(buf+0, buf+3, 3);
assert(!memcmp(buf, "defdefg", 7));
memcpy(buf+5, buf+1, 2);
assert(!memcmp(buf, "defdeef", 7));
memcpy(buf+1, buf+4, 0);
assert(!memcmp(buf, "defdeef", 7));
}
{
char buf[] = "abcdefgh";
memmove(buf+0, buf+1, 7);
assert(!memcmp(buf, "bcdefghh", 8));
buf[7] = 0;
memmove(buf+1, buf+0, 7);
assert(!memcmp(buf, "bbcdefgh", 8));
memmove(buf+2, buf+1, 0);
assert(!memcmp(buf, "bbcdefgh", 8));
}
assert(memcmp("\xff", "1", 1) > 0);
assert(memcmp("", "", 0) == 0); // test empty after > result
assert(memcmp("1", "\xff", 1) < 0);
assert(memcmp("", "", 0) == 0); // test empty after < result
assert(memcmp("ab", "aa", 2) > 0);
assert(memcmp("aa", "ab", 2) < 0);
assert(memcmp("x", "y", 0) == 0);
assert(0 == strlen(""));
assert(1 == strlen(" "));
assert(1 == strlen("\xff"));
assert(5 == strlen("hello"));
return 0;
}
#endif
|
