1 /*
2  * Copyright (C) 2016 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef ART_LIBELFFILE_DWARF_EXPRESSION_H_
18 #define ART_LIBELFFILE_DWARF_EXPRESSION_H_
19 
20 #include <cstddef>
21 #include <cstdint>
22 
23 #include "dwarf/dwarf_constants.h"
24 #include "dwarf/writer.h"
25 
26 namespace art {
27 namespace dwarf {
28 
29 // Writer for DWARF expressions which are used in .debug_info and .debug_loc sections.
30 // See the DWARF specification for the precise meaning of the opcodes.
31 // If multiple equivalent encodings are possible, it will choose the most compact one.
32 // The writer is not exhaustive - it only implements opcodes we have needed so far.
33 class Expression : private Writer<> {
34  public:
35   using Writer<>::data;
36   using Writer<>::size;
37 
38   // Push signed integer on the stack.
WriteOpConsts(int32_t value)39   void WriteOpConsts(int32_t value) {
40     if (0 <= value && value < 32) {
41       PushUint8(DW_OP_lit0 + value);
42     } else {
43       PushUint8(DW_OP_consts);
44       PushSleb128(value);
45     }
46   }
47 
48   // Push unsigned integer on the stack.
WriteOpConstu(uint32_t value)49   void WriteOpConstu(uint32_t value) {
50     if (value < 32) {
51       PushUint8(DW_OP_lit0 + value);
52     } else {
53       PushUint8(DW_OP_constu);
54       PushUleb128(value);
55     }
56   }
57 
58   // Variable is stored in given register.
WriteOpReg(uint32_t dwarf_reg_num)59   void WriteOpReg(uint32_t dwarf_reg_num) {
60     if (dwarf_reg_num < 32) {
61       PushUint8(DW_OP_reg0 + dwarf_reg_num);
62     } else {
63       PushUint8(DW_OP_regx);
64       PushUleb128(dwarf_reg_num);
65     }
66   }
67 
68   // Variable is stored on stack.  Also see DW_AT_frame_base.
WriteOpFbreg(int32_t stack_offset)69   void WriteOpFbreg(int32_t stack_offset) {
70     PushUint8(DW_OP_fbreg);
71     PushSleb128(stack_offset);
72   }
73 
74   // The variable is stored in multiple locations (pieces).
WriteOpPiece(uint32_t num_bytes)75   void WriteOpPiece(uint32_t num_bytes) {
76     PushUint8(DW_OP_piece);
77     PushUleb128(num_bytes);
78   }
79 
80   // Loads 32-bit or 64-bit value depending on architecture.
WriteOpDeref()81   void WriteOpDeref() { PushUint8(DW_OP_deref); }
82 
83   // Loads value of given byte size.
WriteOpDerefSize(uint8_t num_bytes)84   void WriteOpDerefSize(uint8_t num_bytes) {
85     PushUint8(DW_OP_deref_size);
86     PushUint8(num_bytes);
87   }
88 
89   // Pop two values and push their sum.
WriteOpPlus()90   void WriteOpPlus() { PushUint8(DW_OP_plus); }
91 
92   // Add constant value to value on top of stack.
WriteOpPlusUconst(uint32_t offset)93   void WriteOpPlusUconst(uint32_t offset) {
94     PushUint8(DW_OP_plus_uconst);
95     PushUleb128(offset);
96   }
97 
98   // Negate top of stack.
WriteOpNeg()99   void WriteOpNeg() { PushUint8(DW_OP_neg); }
100 
101   // Pop two values and push their bitwise-AND.
WriteOpAnd()102   void WriteOpAnd() { PushUint8(DW_OP_and); }
103 
104   // Push stack base pointer as determined from .debug_frame.
WriteOpCallFrameCfa()105   void WriteOpCallFrameCfa() { PushUint8(DW_OP_call_frame_cfa); }
106 
107   // Push address of the variable we are working with.
WriteOpPushObjectAddress()108   void WriteOpPushObjectAddress() { PushUint8(DW_OP_push_object_address); }
109 
110   // Return the top stack as the value of the variable.
111   // Otherwise, the top of stack is the variable's location.
WriteOpStackValue()112   void WriteOpStackValue() { PushUint8(DW_OP_stack_value); }
113 
Expression(std::vector<uint8_t> * buffer)114   explicit Expression(std::vector<uint8_t>* buffer) : Writer<>(buffer) {
115     buffer->clear();
116   }
117 };
118 }  // namespace dwarf
119 }  // namespace art
120 
121 #endif  // ART_LIBELFFILE_DWARF_EXPRESSION_H_
122