1 // Copyright 2009 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef V8_REGEXP_REGEXP_STACK_H_
6 #define V8_REGEXP_REGEXP_STACK_H_
7 
8 #include "src/base/logging.h"
9 #include "src/base/macros.h"
10 #include "src/globals.h"
11 
12 namespace v8 {
13 namespace internal {
14 
15 class RegExpStack;
16 
17 // Maintains a per-v8thread stack area that can be used by irregexp
18 // implementation for its backtracking stack.
19 // Since there is only one stack area, the Irregexp implementation is not
20 // re-entrant. I.e., no regular expressions may be executed in the same thread
21 // during a preempted Irregexp execution.
22 class RegExpStackScope {
23  public:
24   // Create and delete an instance to control the life-time of a growing stack.
25 
26   // Initializes the stack memory area if necessary.
27   explicit RegExpStackScope(Isolate* isolate);
28   ~RegExpStackScope();  // Releases the stack if it has grown.
29 
stack()30   RegExpStack* stack() const { return regexp_stack_; }
31 
32  private:
33   RegExpStack* regexp_stack_;
34 
35   DISALLOW_COPY_AND_ASSIGN(RegExpStackScope);
36 };
37 
38 
39 class RegExpStack {
40  public:
41   // Number of allocated locations on the stack below the limit.
42   // No sequence of pushes must be longer that this without doing a stack-limit
43   // check.
44   static const int kStackLimitSlack = 32;
45 
46   // Gives the top of the memory used as stack.
stack_base()47   Address stack_base() {
48     DCHECK_NE(0, thread_local_.memory_size_);
49     return reinterpret_cast<Address>(thread_local_.memory_) +
50            thread_local_.memory_size_;
51   }
52 
53   // The total size of the memory allocated for the stack.
stack_capacity()54   size_t stack_capacity() { return thread_local_.memory_size_; }
55 
56   // If the stack pointer gets below the limit, we should react and
57   // either grow the stack or report an out-of-stack exception.
58   // There is only a limited number of locations below the stack limit,
59   // so users of the stack should check the stack limit during any
60   // sequence of pushes longer that this.
limit_address()61   Address* limit_address() { return &(thread_local_.limit_); }
62 
63   // Ensures that there is a memory area with at least the specified size.
64   // If passing zero, the default/minimum size buffer is allocated.
65   Address EnsureCapacity(size_t size);
66 
67   // Thread local archiving.
ArchiveSpacePerThread()68   static int ArchiveSpacePerThread() {
69     return static_cast<int>(sizeof(ThreadLocal));
70   }
71   char* ArchiveStack(char* to);
72   char* RestoreStack(char* from);
FreeThreadResources()73   void FreeThreadResources() { thread_local_.Free(); }
74 
75  private:
76   RegExpStack();
77   ~RegExpStack();
78 
79   // Artificial limit used when no memory has been allocated.
80   static const Address kMemoryTop =
81       static_cast<Address>(static_cast<uintptr_t>(-1));
82 
83   // Minimal size of allocated stack area.
84   static const size_t kMinimumStackSize = 1 * KB;
85 
86   // Maximal size of allocated stack area.
87   static const size_t kMaximumStackSize = 64 * MB;
88 
89   // Structure holding the allocated memory, size and limit.
90   struct ThreadLocal {
ThreadLocalThreadLocal91     ThreadLocal() { Clear(); }
92     // If memory_size_ > 0 then memory_ must be non-nullptr.
93     byte* memory_;
94     size_t memory_size_;
95     Address limit_;
ClearThreadLocal96     void Clear() {
97       memory_ = nullptr;
98       memory_size_ = 0;
99       limit_ = kMemoryTop;
100     }
101     void Free();
102   };
103 
104   // Address of allocated memory.
memory_address()105   Address memory_address() {
106     return reinterpret_cast<Address>(&thread_local_.memory_);
107   }
108 
109   // Address of size of allocated memory.
memory_size_address()110   Address memory_size_address() {
111     return reinterpret_cast<Address>(&thread_local_.memory_size_);
112   }
113 
114   // Resets the buffer if it has grown beyond the default/minimum size.
115   // After this, the buffer is either the default size, or it is empty, so
116   // you have to call EnsureCapacity before using it again.
117   void Reset();
118 
119   ThreadLocal thread_local_;
120   Isolate* isolate_;
121 
122   friend class ExternalReference;
123   friend class Isolate;
124   friend class RegExpStackScope;
125 
126   DISALLOW_COPY_AND_ASSIGN(RegExpStack);
127 };
128 
129 }  // namespace internal
130 }  // namespace v8
131 
132 #endif  // V8_REGEXP_REGEXP_STACK_H_
133