1 /*
2  * Copyright (C) 2015 The Android Open Source Project
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  *  * Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  *  * Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in
12  *    the documentation and/or other materials provided with the
13  *    distribution.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19  * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22  * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26  * SUCH DAMAGE.
27  */
28 
29 #ifndef _LINKER_SLEB128_H
30 #define _LINKER_SLEB128_H
31 
32 #include <stdint.h>
33 
34 #include "linker_debug.h"
35 
36 // Helper classes for decoding LEB128, used in packed relocation data.
37 // http://en.wikipedia.org/wiki/LEB128
38 
39 class sleb128_decoder {
40  public:
sleb128_decoder(const uint8_t * buffer,size_t count)41   sleb128_decoder(const uint8_t* buffer, size_t count)
42       : current_(buffer), end_(buffer+count) { }
43 
pop_front()44   size_t pop_front() {
45     size_t value = 0;
46     static const size_t size = CHAR_BIT * sizeof(value);
47 
48     size_t shift = 0;
49     uint8_t byte;
50 
51     do {
52       if (current_ >= end_) {
53         __libc_fatal("sleb128_decoder ran out of bounds");
54       }
55       byte = *current_++;
56       value |= (static_cast<size_t>(byte & 127) << shift);
57       shift += 7;
58     } while (byte & 128);
59 
60     if (shift < size && (byte & 64)) {
61       value |= -(static_cast<size_t>(1) << shift);
62     }
63 
64     return value;
65   }
66 
67  private:
68   const uint8_t* current_;
69   const uint8_t* const end_;
70 };
71 
72 #endif // __LINKER_SLEB128_H
73