summaryrefslogtreecommitdiff
path: root/src/malloc/mallocng/meta.h
blob: 61ec53f9a589941c5edb29da0f6fa9342faf42ab (plain) (blame)
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
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
#ifndef MALLOC_META_H
#define MALLOC_META_H

#include <stdint.h>
#include <errno.h>
#include <limits.h>
#include "glue.h"

__attribute__((__visibility__("hidden")))
extern const uint16_t size_classes[];

#define MMAP_THRESHOLD 131052

#define UNIT 16
#define IB 4

struct group {
	struct meta *meta;
	unsigned char active_idx:5;
	char pad[UNIT - sizeof(struct meta *) - 1];
	unsigned char storage[];
};

struct meta {
	struct meta *prev, *next;
	struct group *mem;
	volatile int avail_mask, freed_mask;
	uintptr_t last_idx:5;
	uintptr_t freeable:1;
	uintptr_t sizeclass:6;
	uintptr_t maplen:8*sizeof(uintptr_t)-12;
};

struct meta_area {
	uint64_t check;
	struct meta_area *next;
	int nslots;
	struct meta slots[];
};

struct malloc_context {
	uint64_t secret;
#ifndef PAGESIZE
	size_t pagesize;
#endif
	int init_done;
	unsigned mmap_counter;
	struct meta *free_meta_head;
	struct meta *avail_meta;
	size_t avail_meta_count, avail_meta_area_count, meta_alloc_shift;
	struct meta_area *meta_area_head, *meta_area_tail;
	unsigned char *avail_meta_areas;
	struct meta *active[48];
	size_t usage_by_class[48];
	uint8_t unmap_seq[32], bounces[32];
	uint8_t seq;
	uintptr_t brk;
};

__attribute__((__visibility__("hidden")))
extern struct malloc_context ctx;

#ifdef PAGESIZE
#define PGSZ PAGESIZE
#else
#define PGSZ ctx.pagesize
#endif

__attribute__((__visibility__("hidden")))
struct meta *alloc_meta(void);

__attribute__((__visibility__("hidden")))
int is_allzero(void *);

static inline void queue(struct meta **phead, struct meta *m)
{
	assert(!m->next);
	assert(!m->prev);
	if (*phead) {
		struct meta *head = *phead;
		m->next = head;
		m->prev = head->prev;
		m->next->prev = m->prev->next = m;
	} else {
		m->prev = m->next = m;
		*phead = m;
	}
}

static inline void dequeue(struct meta **phead, struct meta *m)
{
	if (m->next != m) {
		m->prev->next = m->next;
		m->next->prev = m->prev;
		if (*phead == m) *phead = m->next;
	} else {
		*phead = 0;
	}
	m->prev = m->next = 0;
}

static inline struct meta *dequeue_head(struct meta **phead)
{
	struct meta *m = *phead;
	if (m) dequeue(phead, m);
	return m;
}

static inline void free_meta(struct meta *m)
{
	*m = (struct meta){0};
	queue(&ctx.free_meta_head, m);
}

static inline uint32_t activate_group(struct meta *m)
{
	assert(!m->avail_mask);
	uint32_t mask, act = (2u<<m->mem->active_idx)-1;
	do mask = m->freed_mask;
	while (a_cas(&m->freed_mask, mask, mask&~act)!=mask);
	return m->avail_mask = mask & act;
}

static inline int get_slot_index(const unsigned char *p)
{
	return p[-3] & 31;
}

static inline struct meta *get_meta(const unsigned char *p)
{
	assert(!((uintptr_t)p & 15));
	int offset = *(const uint16_t *)(p - 2);
	int index = get_slot_index(p);
	if (p[-4]) {
		assert(!offset);
		offset = *(uint32_t *)(p - 8);
		assert(offset > 0xffff);
	}
	const struct group *base = (const void *)(p - UNIT*offset - UNIT);
	const struct meta *meta = base->meta;
	assert(meta->mem == base);
	assert(index <= meta->last_idx);
	assert(!(meta->avail_mask & (1u<<index)));
	assert(!(meta->freed_mask & (1u<<index)));
	const struct meta_area *area = (void *)((uintptr_t)meta & -4096);
	assert(area->check == ctx.secret);
	if (meta->sizeclass < 48) {
		assert(offset >= size_classes[meta->sizeclass]*index);
		assert(offset < size_classes[meta->sizeclass]*(index+1));
	} else {
		assert(meta->sizeclass == 63);
	}
	if (meta->maplen) {
		assert(offset <= meta->maplen*4096UL/UNIT - 1);
	}
	return (struct meta *)meta;
}

static inline size_t get_nominal_size(const unsigned char *p, const unsigned char *end)
{
	size_t reserved = p[-3] >> 5;
	if (reserved >= 5) {
		assert(reserved == 5);
		reserved = *(const uint32_t *)(end-4);
		assert(reserved >= 5);
		assert(!end[-5]);
	}
	assert(reserved <= end-p);
	assert(!*(end-reserved));
	// also check the slot's overflow byte
	assert(!*end);
	return end-reserved-p;
}

static inline size_t get_stride(const struct meta *g)
{
	if (!g->last_idx && g->maplen) {
		return g->maplen*4096UL - UNIT;
	} else {
		return UNIT*size_classes[g->sizeclass];
	}
}

static inline void set_size(unsigned char *p, unsigned char *end, size_t n)
{
	int reserved = end-p-n;
	if (reserved) end[-reserved] = 0;
	if (reserved >= 5) {
		*(uint32_t *)(end-4) = reserved;
		end[-5] = 0;
		reserved = 5;
	}
	p[-3] = (p[-3]&31) + (reserved<<5);
}

static inline void *enframe(struct meta *g, int idx, size_t n, int ctr)
{
	size_t stride = get_stride(g);
	size_t slack = (stride-IB-n)/UNIT;
	unsigned char *p = g->mem->storage + stride*idx;
	unsigned char *end = p+stride-IB;
	// cycle offset within slot to increase interval to address
	// reuse, facilitate trapping double-free.
	int off = (p[-3] ? *(uint16_t *)(p-2) + 1 : ctr) & 255;
	assert(!p[-4]);
	if (off > slack) {
		size_t m = slack;
		m |= m>>1; m |= m>>2; m |= m>>4;
		off &= m;
		if (off > slack) off -= slack+1;
		assert(off <= slack);
	}
	if (off) {
		// store offset in unused header at offset zero
		// if enframing at non-zero offset.
		*(uint16_t *)(p-2) = off;
		p[-3] = 7<<5;
		p += UNIT*off;
		// for nonzero offset there is no permanent check
		// byte, so make one.
		p[-4] = 0;
	}
	*(uint16_t *)(p-2) = (size_t)(p-g->mem->storage)/UNIT;
	p[-3] = idx;
	set_size(p, end, n);
	return p;
}

static inline int size_to_class(size_t n)
{
	n = (n+IB-1)>>4;
	if (n<10) return n;
	n++;
	int i = (28-a_clz_32(n))*4 + 8;
	if (n>size_classes[i+1]) i+=2;
	if (n>size_classes[i]) i++;
	return i;
}

static inline int size_overflows(size_t n)
{
	if (n >= SIZE_MAX/2 - 4096) {
		errno = ENOMEM;
		return 1;
	}
	return 0;
}

static inline void step_seq(void)
{
	if (ctx.seq==255) {
		for (int i=0; i<32; i++) ctx.unmap_seq[i] = 0;
		ctx.seq = 1;
	} else {
		ctx.seq++;
	}
}

static inline void record_seq(int sc)
{
	if (sc-7U < 32) ctx.unmap_seq[sc-7] = ctx.seq;
}

static inline void account_bounce(int sc)
{
	if (sc-7U < 32) {
		int seq = ctx.unmap_seq[sc-7];
		if (seq && ctx.seq-seq < 10) {
			if (ctx.bounces[sc-7]+1 < 100)
				ctx.bounces[sc-7]++;
			else
				ctx.bounces[sc-7] = 150;
		}
	}
}

static inline void decay_bounces(int sc)
{
	if (sc-7U < 32 && ctx.bounces[sc-7])
		ctx.bounces[sc-7]--;
}

static inline int is_bouncing(int sc)
{
	return (sc-7U < 32 && ctx.bounces[sc-7] >= 100);
}

#endif