1 //===-- ARMUnwindOpAsm.cpp - ARM Unwind Opcodes Assembler -------*- 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 // This file implements the unwind opcode assembler for ARM exception handling
10 // table.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "ARMUnwindOpAsm.h"
15 #include "llvm/Support/ARMEHABI.h"
16 #include "llvm/Support/LEB128.h"
17 #include "llvm/Support/MathExtras.h"
18 #include <cassert>
19 
20 using namespace llvm;
21 
22 namespace {
23 
24   /// UnwindOpcodeStreamer - The simple wrapper over SmallVector to emit bytes
25   /// with MSB to LSB per uint32_t ordering.  For example, the first byte will
26   /// be placed in Vec[3], and the following bytes will be placed in 2, 1, 0,
27   /// 7, 6, 5, 4, 11, 10, 9, 8, and so on.
28   class UnwindOpcodeStreamer {
29   private:
30     SmallVectorImpl<uint8_t> &Vec;
31     size_t Pos = 3;
32 
33   public:
34     UnwindOpcodeStreamer(SmallVectorImpl<uint8_t> &V) : Vec(V) {}
35 
36     /// Emit the byte in MSB to LSB per uint32_t order.
37     void EmitByte(uint8_t elem) {
38       Vec[Pos] = elem;
39       Pos = (((Pos ^ 0x3u) + 1) ^ 0x3u);
40     }
41 
42     /// Emit the size prefix.
43     void EmitSize(size_t Size) {
44       size_t SizeInWords = (Size + 3) / 4;
45       assert(SizeInWords <= 0x100u &&
46              "Only 256 additional words are allowed for unwind opcodes");
47       EmitByte(static_cast<uint8_t>(SizeInWords - 1));
48     }
49 
50     /// Emit the personality index prefix.
51     void EmitPersonalityIndex(unsigned PI) {
52       assert(PI < ARM::EHABI::NUM_PERSONALITY_INDEX &&
53              "Invalid personality prefix");
54       EmitByte(ARM::EHABI::EHT_COMPACT | PI);
55     }
56 
57     /// Fill the rest of bytes with FINISH opcode.
58     void FillFinishOpcode() {
59       while (Pos < Vec.size())
60         EmitByte(ARM::EHABI::UNWIND_OPCODE_FINISH);
61     }
62   };
63 
64 } // end anonymous namespace
65 
66 void UnwindOpcodeAssembler::EmitRegSave(uint32_t RegSave) {
67   if (RegSave == 0u)
68     return;
69 
70   // One byte opcode to save register r14 and r11-r4
71   if (RegSave & (1u << 4)) {
72     // The one byte opcode will always save r4, thus we can't use the one byte
73     // opcode when r4 is not in .save directive.
74 
75     // Compute the consecutive registers from r4 to r11.
76     uint32_t Mask = RegSave & 0xff0u;
77     uint32_t Range = countTrailingOnes(Mask >> 5); // Exclude r4.
78     // Mask off non-consecutive registers. Keep r4.
79     Mask &= ~(0xffffffe0u << Range);
80 
81     // Emit this opcode when the mask covers every registers.
82     uint32_t UnmaskedReg = RegSave & 0xfff0u & (~Mask);
83     if (UnmaskedReg == 0u) {
84       // Pop r[4 : (4 + n)]
85       EmitInt8(ARM::EHABI::UNWIND_OPCODE_POP_REG_RANGE_R4 | Range);
86       RegSave &= 0x000fu;
87     } else if (UnmaskedReg == (1u << 14)) {
88       // Pop r[14] + r[4 : (4 + n)]
89       EmitInt8(ARM::EHABI::UNWIND_OPCODE_POP_REG_RANGE_R4_R14 | Range);
90       RegSave &= 0x000fu;
91     }
92   }
93 
94   // Two bytes opcode to save register r15-r4
95   if ((RegSave & 0xfff0u) != 0)
96     EmitInt16(ARM::EHABI::UNWIND_OPCODE_POP_REG_MASK_R4 | (RegSave >> 4));
97 
98   // Opcode to save register r3-r0
99   if ((RegSave & 0x000fu) != 0)
100     EmitInt16(ARM::EHABI::UNWIND_OPCODE_POP_REG_MASK | (RegSave & 0x000fu));
101 }
102 
103 /// Emit unwind opcodes for .vsave directives
104 void UnwindOpcodeAssembler::EmitVFPRegSave(uint32_t VFPRegSave) {
105   // We only have 4 bits to save the offset in the opcode so look at the lower
106   // and upper 16 bits separately.
107   for (uint32_t Regs : {VFPRegSave & 0xffff0000u, VFPRegSave & 0x0000ffffu}) {
108     while (Regs) {
109       // Now look for a run of set bits. Remember the MSB and LSB of the run.
110       auto RangeMSB = 32 - countLeadingZeros(Regs);
111       auto RangeLen = countLeadingOnes(Regs << (32 - RangeMSB));
112       auto RangeLSB = RangeMSB - RangeLen;
113 
114       int Opcode = RangeLSB >= 16
115                        ? ARM::EHABI::UNWIND_OPCODE_POP_VFP_REG_RANGE_FSTMFDD_D16
116                        : ARM::EHABI::UNWIND_OPCODE_POP_VFP_REG_RANGE_FSTMFDD;
117 
118       EmitInt16(Opcode | ((RangeLSB % 16) << 4) | (RangeLen - 1));
119 
120       // Zero out bits we're done with.
121       Regs &= ~(-1u << RangeLSB);
122     }
123   }
124 }
125 
126 /// Emit unwind opcodes to copy address from source register to $sp.
127 void UnwindOpcodeAssembler::EmitSetSP(uint16_t Reg) {
128   EmitInt8(ARM::EHABI::UNWIND_OPCODE_SET_VSP | Reg);
129 }
130 
131 /// Emit unwind opcodes to add $sp with an offset.
132 void UnwindOpcodeAssembler::EmitSPOffset(int64_t Offset) {
133   if (Offset > 0x200) {
134     uint8_t Buff[16];
135     Buff[0] = ARM::EHABI::UNWIND_OPCODE_INC_VSP_ULEB128;
136     size_t ULEBSize = encodeULEB128((Offset - 0x204) >> 2, Buff + 1);
137     emitBytes(Buff, ULEBSize + 1);
138   } else if (Offset > 0) {
139     if (Offset > 0x100) {
140       EmitInt8(ARM::EHABI::UNWIND_OPCODE_INC_VSP | 0x3fu);
141       Offset -= 0x100;
142     }
143     EmitInt8(ARM::EHABI::UNWIND_OPCODE_INC_VSP |
144              static_cast<uint8_t>((Offset - 4) >> 2));
145   } else if (Offset < 0) {
146     while (Offset < -0x100) {
147       EmitInt8(ARM::EHABI::UNWIND_OPCODE_DEC_VSP | 0x3fu);
148       Offset += 0x100;
149     }
150     EmitInt8(ARM::EHABI::UNWIND_OPCODE_DEC_VSP |
151              static_cast<uint8_t>(((-Offset) - 4) >> 2));
152   }
153 }
154 
155 void UnwindOpcodeAssembler::Finalize(unsigned &PersonalityIndex,
156                                      SmallVectorImpl<uint8_t> &Result) {
157   UnwindOpcodeStreamer OpStreamer(Result);
158 
159   if (HasPersonality) {
160     // User-specifed personality routine: [ SIZE , OP1 , OP2 , ... ]
161     PersonalityIndex = ARM::EHABI::NUM_PERSONALITY_INDEX;
162     size_t TotalSize = Ops.size() + 1;
163     size_t RoundUpSize = (TotalSize + 3) / 4 * 4;
164     Result.resize(RoundUpSize);
165     OpStreamer.EmitSize(RoundUpSize);
166   } else {
167     // If no personalityindex is specified, select ane
168     if (PersonalityIndex == ARM::EHABI::NUM_PERSONALITY_INDEX)
169       PersonalityIndex = (Ops.size() <= 3) ? ARM::EHABI::AEABI_UNWIND_CPP_PR0
170                                            : ARM::EHABI::AEABI_UNWIND_CPP_PR1;
171     if (PersonalityIndex == ARM::EHABI::AEABI_UNWIND_CPP_PR0) {
172       // __aeabi_unwind_cpp_pr0: [ 0x80 , OP1 , OP2 , OP3 ]
173       assert(Ops.size() <= 3 && "too many opcodes for __aeabi_unwind_cpp_pr0");
174       Result.resize(4);
175       OpStreamer.EmitPersonalityIndex(PersonalityIndex);
176     } else {
177       // __aeabi_unwind_cpp_pr{1,2}: [ {0x81,0x82} , SIZE , OP1 , OP2 , ... ]
178       size_t TotalSize = Ops.size() + 2;
179       size_t RoundUpSize = (TotalSize + 3) / 4 * 4;
180       Result.resize(RoundUpSize);
181       OpStreamer.EmitPersonalityIndex(PersonalityIndex);
182       OpStreamer.EmitSize(RoundUpSize);
183     }
184   }
185 
186   // Copy the unwind opcodes
187   for (size_t i = OpBegins.size() - 1; i > 0; --i)
188     for (size_t j = OpBegins[i - 1], end = OpBegins[i]; j < end; ++j)
189       OpStreamer.EmitByte(Ops[j]);
190 
191   // Emit the padding finish opcodes if the size is not multiple of 4.
192   OpStreamer.FillFinishOpcode();
193 
194   // Reset the assembler state
195   Reset();
196 }
197