1 //===- StreamingMemoryObject.cpp - Streamable data interface -------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "llvm/Support/StreamingMemoryObject.h"
11 #include <cassert>
12 #include <cstddef>
13 #include <cstring>
14 using namespace llvm;
15 
16 namespace {
17 
18 class RawMemoryObject : public MemoryObject {
19 public:
20   RawMemoryObject(const unsigned char *Start, const unsigned char *End) :
21     FirstChar(Start), LastChar(End) {
22     assert(LastChar >= FirstChar && "Invalid start/end range");
23   }
24 
25   uint64_t getExtent() const override {
26     return LastChar - FirstChar;
27   }
28   uint64_t readBytes(uint8_t *Buf, uint64_t Size,
29                      uint64_t Address) const override;
30   const uint8_t *getPointer(uint64_t address, uint64_t size) const override;
31   bool isValidAddress(uint64_t address) const override {
32     return validAddress(address);
33   }
34 
35 private:
36   const uint8_t* const FirstChar;
37   const uint8_t* const LastChar;
38 
39   // These are implemented as inline functions here to avoid multiple virtual
40   // calls per public function
41   bool validAddress(uint64_t address) const {
42     return static_cast<std::ptrdiff_t>(address) < LastChar - FirstChar;
43   }
44 
45   RawMemoryObject(const RawMemoryObject&) = delete;
46   void operator=(const RawMemoryObject&) = delete;
47 };
48 
49 uint64_t RawMemoryObject::readBytes(uint8_t *Buf, uint64_t Size,
50                                     uint64_t Address) const {
51   uint64_t BufferSize = LastChar - FirstChar;
52   if (Address >= BufferSize)
53     return 0;
54 
55   uint64_t End = Address + Size;
56   if (End > BufferSize)
57     End = BufferSize;
58 
59   assert(static_cast<int64_t>(End - Address) >= 0);
60   Size = End - Address;
61   memcpy(Buf, Address + FirstChar, Size);
62   return Size;
63 }
64 
65 const uint8_t *RawMemoryObject::getPointer(uint64_t address,
66                                            uint64_t size) const {
67   return FirstChar + address;
68 }
69 } // anonymous namespace
70 
71 namespace llvm {
72 // If the bitcode has a header, then its size is known, and we don't have to
73 // block until we actually want to read it.
74 bool StreamingMemoryObject::isValidAddress(uint64_t address) const {
75   if (ObjectSize && address < ObjectSize) return true;
76   return fetchToPos(address);
77 }
78 
79 uint64_t StreamingMemoryObject::getExtent() const {
80   if (ObjectSize) return ObjectSize;
81   size_t pos = BytesRead + kChunkSize;
82   // keep fetching until we run out of bytes
83   while (fetchToPos(pos)) pos += kChunkSize;
84   return ObjectSize;
85 }
86 
87 uint64_t StreamingMemoryObject::readBytes(uint8_t *Buf, uint64_t Size,
88                                           uint64_t Address) const {
89   fetchToPos(Address + Size - 1);
90   // Note: For wrapped bitcode files will set ObjectSize after the
91   // first call to fetchToPos. In such cases, ObjectSize can be
92   // smaller than BytesRead.
93   size_t MaxAddress =
94       (ObjectSize && ObjectSize < BytesRead) ? ObjectSize : BytesRead;
95   if (Address >= MaxAddress)
96     return 0;
97 
98   uint64_t End = Address + Size;
99   if (End > MaxAddress)
100     End = MaxAddress;
101   assert(End >= Address);
102   Size = End - Address;
103   memcpy(Buf, &Bytes[Address + BytesSkipped], Size);
104   return Size;
105 }
106 
107 const uint8_t *StreamingMemoryObject::getPointer(uint64_t Address,
108                                                  uint64_t Size) const {
109   fetchToPos(Address + Size - 1);
110   return &Bytes[Address + BytesSkipped];
111 }
112 
113 bool StreamingMemoryObject::dropLeadingBytes(size_t s) {
114   if (BytesRead < s) return true;
115   BytesSkipped = s;
116   BytesRead -= s;
117   return false;
118 }
119 
120 void StreamingMemoryObject::setKnownObjectSize(size_t size) {
121   ObjectSize = size;
122   Bytes.reserve(size);
123   if (ObjectSize <= BytesRead)
124     EOFReached = true;
125 }
126 
127 MemoryObject *getNonStreamedMemoryObject(const unsigned char *Start,
128                                          const unsigned char *End) {
129   return new RawMemoryObject(Start, End);
130 }
131 
132 StreamingMemoryObject::StreamingMemoryObject(
133     std::unique_ptr<DataStreamer> Streamer)
134     : Bytes(kChunkSize), Streamer(std::move(Streamer)), BytesRead(0),
135       BytesSkipped(0), ObjectSize(0), EOFReached(false) {
136   BytesRead = this->Streamer->GetBytes(&Bytes[0], kChunkSize);
137 }
138 }
139