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//===-- sanitizer_stackdepot.cc -------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file is shared between AddressSanitizer and ThreadSanitizer
// run-time libraries.
//===----------------------------------------------------------------------===//
#include "sanitizer_stackdepot.h"
#include "sanitizer_common.h"
#include "sanitizer_internal_defs.h"
#include "sanitizer_mutex.h"
#include "sanitizer_atomic.h"
namespace __sanitizer {
const int kTabSize = 1024 * 1024; // Hash table size.
const int kPartBits = 8;
const int kPartShift = sizeof(u32) * 8 - kPartBits - 1;
const int kPartCount = 1 << kPartBits; // Number of subparts in the table.
const int kPartSize = kTabSize / kPartCount;
const int kMaxId = 1 << kPartShift;
struct StackDesc {
StackDesc *link;
u32 id;
u32 hash;
uptr size;
uptr stack[1]; // [size]
};
static struct {
StaticSpinMutex mtx; // Protects alloc of new blocks for region allocator.
atomic_uintptr_t region_pos; // Region allocator for StackDesc's.
atomic_uintptr_t region_end;
atomic_uintptr_t tab[kTabSize]; // Hash table of StackDesc's.
atomic_uint32_t seq[kPartCount]; // Unique id generators.
} depot;
static StackDepotStats stats;
StackDepotStats *StackDepotGetStats() {
return &stats;
}
static u32 hash(const uptr *stack, uptr size) {
// murmur2
const u32 m = 0x5bd1e995;
const u32 seed = 0x9747b28c;
const u32 r = 24;
u32 h = seed ^ (size * sizeof(uptr));
for (uptr i = 0; i < size; i++) {
u32 k = stack[i];
k *= m;
k ^= k >> r;
k *= m;
h *= m;
h ^= k;
}
h ^= h >> 13;
h *= m;
h ^= h >> 15;
return h;
}
static StackDesc *tryallocDesc(uptr memsz) {
// Optimisic lock-free allocation, essentially try to bump the region ptr.
for (;;) {
uptr cmp = atomic_load(&depot.region_pos, memory_order_acquire);
uptr end = atomic_load(&depot.region_end, memory_order_acquire);
if (cmp == 0 || cmp + memsz > end)
return 0;
if (atomic_compare_exchange_weak(
&depot.region_pos, &cmp, cmp + memsz,
memory_order_acquire))
return (StackDesc*)cmp;
}
}
static StackDesc *allocDesc(uptr size) {
// First, try to allocate optimisitically.
uptr memsz = sizeof(StackDesc) + (size - 1) * sizeof(uptr);
StackDesc *s = tryallocDesc(memsz);
if (s)
return s;
// If failed, lock, retry and alloc new superblock.
SpinMutexLock l(&depot.mtx);
for (;;) {
s = tryallocDesc(memsz);
if (s)
return s;
atomic_store(&depot.region_pos, 0, memory_order_relaxed);
uptr allocsz = 64 * 1024;
if (allocsz < memsz)
allocsz = memsz;
uptr mem = (uptr)MmapOrDie(allocsz, "stack depot");
stats.mapped += allocsz;
atomic_store(&depot.region_end, mem + allocsz, memory_order_release);
atomic_store(&depot.region_pos, mem, memory_order_release);
}
}
static u32 find(StackDesc *s, const uptr *stack, uptr size, u32 hash) {
// Searches linked list s for the stack, returns its id.
for (; s; s = s->link) {
if (s->hash == hash && s->size == size) {
uptr i = 0;
for (; i < size; i++) {
if (stack[i] != s->stack[i])
break;
}
if (i == size)
return s->id;
}
}
return 0;
}
static StackDesc *lock(atomic_uintptr_t *p) {
// Uses the pointer lsb as mutex.
for (int i = 0;; i++) {
uptr cmp = atomic_load(p, memory_order_relaxed);
if ((cmp & 1) == 0
&& atomic_compare_exchange_weak(p, &cmp, cmp | 1,
memory_order_acquire))
return (StackDesc*)cmp;
if (i < 10)
proc_yield(10);
else
internal_sched_yield();
}
}
static void unlock(atomic_uintptr_t *p, StackDesc *s) {
DCHECK_EQ((uptr)s & 1, 0);
atomic_store(p, (uptr)s, memory_order_release);
}
u32 StackDepotPut(const uptr *stack, uptr size) {
if (stack == 0 || size == 0)
return 0;
uptr h = hash(stack, size);
atomic_uintptr_t *p = &depot.tab[h % kTabSize];
uptr v = atomic_load(p, memory_order_consume);
StackDesc *s = (StackDesc*)(v & ~1);
// First, try to find the existing stack.
u32 id = find(s, stack, size, h);
if (id)
return id;
// If failed, lock, retry and insert new.
StackDesc *s2 = lock(p);
if (s2 != s) {
id = find(s2, stack, size, h);
if (id) {
unlock(p, s2);
return id;
}
}
uptr part = (h % kTabSize) / kPartSize;
id = atomic_fetch_add(&depot.seq[part], 1, memory_order_relaxed) + 1;
stats.n_uniq_ids++;
CHECK_LT(id, kMaxId);
id |= part << kPartShift;
CHECK_NE(id, 0);
CHECK_EQ(id & (1u << 31), 0);
s = allocDesc(size);
s->id = id;
s->hash = h;
s->size = size;
internal_memcpy(s->stack, stack, size * sizeof(uptr));
s->link = s2;
unlock(p, s);
return id;
}
const uptr *StackDepotGet(u32 id, uptr *size) {
if (id == 0)
return 0;
CHECK_EQ(id & (1u << 31), 0);
// High kPartBits contain part id, so we need to scan at most kPartSize lists.
uptr part = id >> kPartShift;
for (int i = 0; i != kPartSize; i++) {
uptr idx = part * kPartSize + i;
CHECK_LT(idx, kTabSize);
atomic_uintptr_t *p = &depot.tab[idx];
uptr v = atomic_load(p, memory_order_consume);
StackDesc *s = (StackDesc*)(v & ~1);
for (; s; s = s->link) {
if (s->id == id) {
*size = s->size;
return s->stack;
}
}
}
*size = 0;
return 0;
}
} // namespace __sanitizer
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