1 //===-- sanitizer_persistent_allocator.h ------------------------*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // A fast memory allocator that does not support free() nor realloc().
10 // All allocations are forever.
11 //===----------------------------------------------------------------------===//
12
13 #ifndef SANITIZER_PERSISTENT_ALLOCATOR_H
14 #define SANITIZER_PERSISTENT_ALLOCATOR_H
15
16 #include "sanitizer_internal_defs.h"
17 #include "sanitizer_mutex.h"
18 #include "sanitizer_atomic.h"
19 #include "sanitizer_common.h"
20
21 namespace __sanitizer {
22
23 class PersistentAllocator {
24 public:
25 void *alloc(uptr size);
26
27 private:
28 void *tryAlloc(uptr size);
29 StaticSpinMutex mtx; // Protects alloc of new blocks for region allocator.
30 atomic_uintptr_t region_pos; // Region allocator for Node's.
31 atomic_uintptr_t region_end;
32 };
33
tryAlloc(uptr size)34 inline void *PersistentAllocator::tryAlloc(uptr size) {
35 // Optimisic lock-free allocation, essentially try to bump the region ptr.
36 for (;;) {
37 uptr cmp = atomic_load(®ion_pos, memory_order_acquire);
38 uptr end = atomic_load(®ion_end, memory_order_acquire);
39 if (cmp == 0 || cmp + size > end) return nullptr;
40 if (atomic_compare_exchange_weak(®ion_pos, &cmp, cmp + size,
41 memory_order_acquire))
42 return (void *)cmp;
43 }
44 }
45
alloc(uptr size)46 inline void *PersistentAllocator::alloc(uptr size) {
47 // First, try to allocate optimisitically.
48 void *s = tryAlloc(size);
49 if (s) return s;
50 // If failed, lock, retry and alloc new superblock.
51 SpinMutexLock l(&mtx);
52 for (;;) {
53 s = tryAlloc(size);
54 if (s) return s;
55 atomic_store(®ion_pos, 0, memory_order_relaxed);
56 uptr allocsz = 64 * 1024;
57 if (allocsz < size) allocsz = size;
58 uptr mem = (uptr)MmapOrDie(allocsz, "stack depot");
59 atomic_store(®ion_end, mem + allocsz, memory_order_release);
60 atomic_store(®ion_pos, mem, memory_order_release);
61 }
62 }
63
64 extern PersistentAllocator thePersistentAllocator;
PersistentAlloc(uptr sz)65 inline void *PersistentAlloc(uptr sz) {
66 return thePersistentAllocator.alloc(sz);
67 }
68
69 } // namespace __sanitizer
70
71 #endif // SANITIZER_PERSISTENT_ALLOCATOR_H
72