1 //===-- ArchitectureMips.cpp ----------------------------------------------===//
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 #include "Plugins/Architecture/Mips/ArchitectureMips.h"
10 #include "lldb/Core/Address.h"
11 #include "lldb/Core/Disassembler.h"
12 #include "lldb/Core/Module.h"
13 #include "lldb/Core/PluginManager.h"
14 #include "lldb/Symbol/Function.h"
15 #include "lldb/Symbol/SymbolContext.h"
16 #include "lldb/Target/SectionLoadList.h"
17 #include "lldb/Target/Target.h"
18 #include "lldb/Utility/ArchSpec.h"
19 #include "lldb/Utility/Log.h"
20 
21 using namespace lldb_private;
22 using namespace lldb;
23 
24 LLDB_PLUGIN_DEFINE(ArchitectureMips)
25 
26 ConstString ArchitectureMips::GetPluginNameStatic() {
27   return ConstString("mips");
28 }
29 
30 void ArchitectureMips::Initialize() {
31   PluginManager::RegisterPlugin(GetPluginNameStatic(),
32                                 "Mips-specific algorithms",
33                                 &ArchitectureMips::Create);
34 }
35 
36 void ArchitectureMips::Terminate() {
37   PluginManager::UnregisterPlugin(&ArchitectureMips::Create);
38 }
39 
40 std::unique_ptr<Architecture> ArchitectureMips::Create(const ArchSpec &arch) {
41   return arch.IsMIPS() ?
42       std::unique_ptr<Architecture>(new ArchitectureMips(arch)) : nullptr;
43 }
44 
45 ConstString ArchitectureMips::GetPluginName() { return GetPluginNameStatic(); }
46 uint32_t ArchitectureMips::GetPluginVersion() { return 1; }
47 
48 addr_t ArchitectureMips::GetCallableLoadAddress(addr_t code_addr,
49                                                 AddressClass addr_class) const {
50   bool is_alternate_isa = false;
51 
52   switch (addr_class) {
53   case AddressClass::eData:
54   case AddressClass::eDebug:
55     return LLDB_INVALID_ADDRESS;
56   case AddressClass::eCodeAlternateISA:
57     is_alternate_isa = true;
58     break;
59   default: break;
60   }
61 
62   if ((code_addr & 2ull) || is_alternate_isa)
63     return code_addr | 1u;
64   return code_addr;
65 }
66 
67 addr_t ArchitectureMips::GetOpcodeLoadAddress(addr_t opcode_addr,
68                                               AddressClass addr_class) const {
69   switch (addr_class) {
70   case AddressClass::eData:
71   case AddressClass::eDebug:
72     return LLDB_INVALID_ADDRESS;
73   default: break;
74   }
75   return opcode_addr & ~(1ull);
76 }
77 
78 lldb::addr_t ArchitectureMips::GetBreakableLoadAddress(lldb::addr_t addr,
79                                                        Target &target) const {
80 
81   Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_BREAKPOINTS));
82 
83   Address resolved_addr;
84 
85   SectionLoadList &section_load_list = target.GetSectionLoadList();
86   if (section_load_list.IsEmpty())
87     // No sections are loaded, so we must assume we are not running yet and
88     // need to operate only on file address.
89     target.ResolveFileAddress(addr, resolved_addr);
90   else
91     target.ResolveLoadAddress(addr, resolved_addr);
92 
93   addr_t current_offset = 0;
94 
95   // Get the function boundaries to make sure we don't scan back before the
96   // beginning of the current function.
97   ModuleSP temp_addr_module_sp(resolved_addr.GetModule());
98   if (temp_addr_module_sp) {
99     SymbolContext sc;
100     SymbolContextItem resolve_scope =
101         eSymbolContextFunction | eSymbolContextSymbol;
102     temp_addr_module_sp->ResolveSymbolContextForAddress(resolved_addr,
103       resolve_scope, sc);
104     Address sym_addr;
105     if (sc.function)
106       sym_addr = sc.function->GetAddressRange().GetBaseAddress();
107     else if (sc.symbol)
108       sym_addr = sc.symbol->GetAddress();
109 
110     addr_t function_start = sym_addr.GetLoadAddress(&target);
111     if (function_start == LLDB_INVALID_ADDRESS)
112       function_start = sym_addr.GetFileAddress();
113 
114     if (function_start)
115       current_offset = addr - function_start;
116   }
117 
118   // If breakpoint address is start of function then we dont have to do
119   // anything.
120   if (current_offset == 0)
121     return addr;
122 
123   auto insn = GetInstructionAtAddress(target, current_offset, addr);
124 
125   if (nullptr == insn || !insn->HasDelaySlot())
126     return addr;
127 
128   // Adjust the breakable address
129   uint64_t breakable_addr = addr - insn->GetOpcode().GetByteSize();
130   LLDB_LOGF(log,
131             "Target::%s Breakpoint at 0x%8.8" PRIx64
132             " is adjusted to 0x%8.8" PRIx64 " due to delay slot\n",
133             __FUNCTION__, addr, breakable_addr);
134 
135   return breakable_addr;
136 }
137 
138 Instruction *ArchitectureMips::GetInstructionAtAddress(
139     Target &target, const Address &resolved_addr, addr_t symbol_offset) const {
140 
141   auto loop_count = symbol_offset / 2;
142 
143   uint32_t arch_flags = m_arch.GetFlags();
144   bool IsMips16 = arch_flags & ArchSpec::eMIPSAse_mips16;
145   bool IsMicromips = arch_flags & ArchSpec::eMIPSAse_micromips;
146 
147   if (loop_count > 3) {
148     // Scan previous 6 bytes
149     if (IsMips16 | IsMicromips)
150       loop_count = 3;
151     // For mips-only, instructions are always 4 bytes, so scan previous 4
152     // bytes only.
153     else
154       loop_count = 2;
155   }
156 
157   // Create Disassembler Instance
158   lldb::DisassemblerSP disasm_sp(
159     Disassembler::FindPlugin(m_arch, nullptr, nullptr));
160 
161   InstructionList instruction_list;
162   InstructionSP prev_insn;
163   bool prefer_file_cache = true; // Read from file
164   uint32_t inst_to_choose = 0;
165 
166   Address addr = resolved_addr;
167 
168   for (uint32_t i = 1; i <= loop_count; i++) {
169     // Adjust the address to read from.
170     addr.Slide(-2);
171     uint32_t insn_size = 0;
172 
173     disasm_sp->ParseInstructions(target, addr,
174                                  {Disassembler::Limit::Bytes, i * 2}, nullptr,
175                                  prefer_file_cache);
176 
177     uint32_t num_insns = disasm_sp->GetInstructionList().GetSize();
178     if (num_insns) {
179       prev_insn = disasm_sp->GetInstructionList().GetInstructionAtIndex(0);
180       insn_size = prev_insn->GetOpcode().GetByteSize();
181       if (i == 1 && insn_size == 2) {
182         // This looks like a valid 2-byte instruction (but it could be a part
183         // of upper 4 byte instruction).
184         instruction_list.Append(prev_insn);
185         inst_to_choose = 1;
186       }
187       else if (i == 2) {
188         // Here we may get one 4-byte instruction or two 2-byte instructions.
189         if (num_insns == 2) {
190           // Looks like there are two 2-byte instructions above our
191           // breakpoint target address. Now the upper 2-byte instruction is
192           // either a valid 2-byte instruction or could be a part of it's
193           // upper 4-byte instruction. In both cases we don't care because in
194           // this case lower 2-byte instruction is definitely a valid
195           // instruction and whatever i=1 iteration has found out is true.
196           inst_to_choose = 1;
197           break;
198         }
199         else if (insn_size == 4) {
200           // This instruction claims its a valid 4-byte instruction. But it
201           // could be a part of it's upper 4-byte instruction. Lets try
202           // scanning upper 2 bytes to verify this.
203           instruction_list.Append(prev_insn);
204           inst_to_choose = 2;
205         }
206       }
207       else if (i == 3) {
208         if (insn_size == 4)
209           // FIXME: We reached here that means instruction at [target - 4] has
210           // already claimed to be a 4-byte instruction, and now instruction
211           // at [target - 6] is also claiming that it's a 4-byte instruction.
212           // This can not be true. In this case we can not decide the valid
213           // previous instruction so we let lldb set the breakpoint at the
214           // address given by user.
215           inst_to_choose = 0;
216         else
217           // This is straight-forward
218           inst_to_choose = 2;
219         break;
220       }
221     }
222     else {
223       // Decode failed, bytes do not form a valid instruction. So whatever
224       // previous iteration has found out is true.
225       if (i > 1) {
226         inst_to_choose = i - 1;
227         break;
228       }
229     }
230   }
231 
232   // Check if we are able to find any valid instruction.
233   if (inst_to_choose) {
234     if (inst_to_choose > instruction_list.GetSize())
235       inst_to_choose--;
236     return instruction_list.GetInstructionAtIndex(inst_to_choose - 1).get();
237   }
238 
239   return nullptr;
240 }
241