1 //===- DWARFLinkerDeclContext.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 "llvm/DWARFLinker/DWARFLinkerDeclContext.h"
10 #include "llvm/DWARFLinker/DWARFLinkerCompileUnit.h"
11 #include "llvm/DebugInfo/DWARF/DWARFContext.h"
12 #include "llvm/DebugInfo/DWARF/DWARFDie.h"
13 #include "llvm/DebugInfo/DWARF/DWARFUnit.h"
14 
15 namespace llvm {
16 
17 /// Set the last DIE/CU a context was seen in and, possibly invalidate the
18 /// context if it is ambiguous.
19 ///
20 /// In the current implementation, we don't handle overloaded functions well,
21 /// because the argument types are not taken into account when computing the
22 /// DeclContext tree.
23 ///
24 /// Some of this is mitigated byt using mangled names that do contain the
25 /// arguments types, but sometimes (e.g. with function templates) we don't have
26 /// that. In that case, just do not unique anything that refers to the contexts
27 /// we are not able to distinguish.
28 ///
29 /// If a context that is not a namespace appears twice in the same CU, we know
30 /// it is ambiguous. Make it invalid.
31 bool DeclContext::setLastSeenDIE(CompileUnit &U, const DWARFDie &Die) {
32   if (LastSeenCompileUnitID == U.getUniqueID()) {
33     DWARFUnit &OrigUnit = U.getOrigUnit();
34     uint32_t FirstIdx = OrigUnit.getDIEIndex(LastSeenDIE);
35     U.getInfo(FirstIdx).Ctxt = nullptr;
36     return false;
37   }
38 
39   LastSeenCompileUnitID = U.getUniqueID();
40   LastSeenDIE = Die;
41   return true;
42 }
43 
44 PointerIntPair<DeclContext *, 1>
45 DeclContextTree::getChildDeclContext(DeclContext &Context, const DWARFDie &DIE,
46                                      CompileUnit &U, bool InClangModule) {
47   unsigned Tag = DIE.getTag();
48 
49   // FIXME: dsymutil-classic compat: We should bail out here if we
50   // have a specification or an abstract_origin. We will get the
51   // parent context wrong here.
52 
53   switch (Tag) {
54   default:
55     // By default stop gathering child contexts.
56     return PointerIntPair<DeclContext *, 1>(nullptr);
57   case dwarf::DW_TAG_module:
58     break;
59   case dwarf::DW_TAG_compile_unit:
60     return PointerIntPair<DeclContext *, 1>(&Context);
61   case dwarf::DW_TAG_subprogram:
62     // Do not unique anything inside CU local functions.
63     if ((Context.getTag() == dwarf::DW_TAG_namespace ||
64          Context.getTag() == dwarf::DW_TAG_compile_unit) &&
65         !dwarf::toUnsigned(DIE.find(dwarf::DW_AT_external), 0))
66       return PointerIntPair<DeclContext *, 1>(nullptr);
67     LLVM_FALLTHROUGH;
68   case dwarf::DW_TAG_member:
69   case dwarf::DW_TAG_namespace:
70   case dwarf::DW_TAG_structure_type:
71   case dwarf::DW_TAG_class_type:
72   case dwarf::DW_TAG_union_type:
73   case dwarf::DW_TAG_enumeration_type:
74   case dwarf::DW_TAG_typedef:
75     // Artificial things might be ambiguous, because they might be created on
76     // demand. For example implicitly defined constructors are ambiguous
77     // because of the way we identify contexts, and they won't be generated
78     // every time everywhere.
79     if (dwarf::toUnsigned(DIE.find(dwarf::DW_AT_artificial), 0))
80       return PointerIntPair<DeclContext *, 1>(nullptr);
81     break;
82   }
83 
84   StringRef NameRef;
85   StringRef FileRef;
86 
87   if (const char *LinkageName = DIE.getLinkageName())
88     NameRef = StringPool.internString(LinkageName);
89   else if (const char *ShortName = DIE.getShortName())
90     NameRef = StringPool.internString(ShortName);
91 
92   bool IsAnonymousNamespace = NameRef.empty() && Tag == dwarf::DW_TAG_namespace;
93   if (IsAnonymousNamespace) {
94     // FIXME: For dsymutil-classic compatibility. I think uniquing within
95     // anonymous namespaces is wrong. There is no ODR guarantee there.
96     NameRef = "(anonymous namespace)";
97   }
98 
99   if (Tag != dwarf::DW_TAG_class_type && Tag != dwarf::DW_TAG_structure_type &&
100       Tag != dwarf::DW_TAG_union_type &&
101       Tag != dwarf::DW_TAG_enumeration_type && NameRef.empty())
102     return PointerIntPair<DeclContext *, 1>(nullptr);
103 
104   unsigned Line = 0;
105   unsigned ByteSize = std::numeric_limits<uint32_t>::max();
106 
107   if (!InClangModule) {
108     // Gather some discriminating data about the DeclContext we will be
109     // creating: File, line number and byte size. This shouldn't be necessary,
110     // because the ODR is just about names, but given that we do some
111     // approximations with overloaded functions and anonymous namespaces, use
112     // these additional data points to make the process safer.
113     //
114     // This is disabled for clang modules, because forward declarations of
115     // module-defined types do not have a file and line.
116     ByteSize = dwarf::toUnsigned(DIE.find(dwarf::DW_AT_byte_size),
117                                  std::numeric_limits<uint64_t>::max());
118     if (Tag != dwarf::DW_TAG_namespace || IsAnonymousNamespace) {
119       if (unsigned FileNum =
120               dwarf::toUnsigned(DIE.find(dwarf::DW_AT_decl_file), 0)) {
121         if (const auto *LT = U.getOrigUnit().getContext().getLineTableForUnit(
122                 &U.getOrigUnit())) {
123           // FIXME: dsymutil-classic compatibility. I'd rather not
124           // unique anything in anonymous namespaces, but if we do, then
125           // verify that the file and line correspond.
126           if (IsAnonymousNamespace)
127             FileNum = 1;
128 
129           if (LT->hasFileAtIndex(FileNum)) {
130             Line = dwarf::toUnsigned(DIE.find(dwarf::DW_AT_decl_line), 0);
131             // Cache the resolved paths based on the index in the line table,
132             // because calling realpath is expensive.
133             FileRef = getResolvedPath(U, FileNum, *LT);
134           }
135         }
136       }
137     }
138   }
139 
140   if (!Line && NameRef.empty())
141     return PointerIntPair<DeclContext *, 1>(nullptr);
142 
143   // We hash NameRef, which is the mangled name, in order to get most
144   // overloaded functions resolve correctly.
145   //
146   // Strictly speaking, hashing the Tag is only necessary for a
147   // DW_TAG_module, to prevent uniquing of a module and a namespace
148   // with the same name.
149   //
150   // FIXME: dsymutil-classic won't unique the same type presented
151   // once as a struct and once as a class. Using the Tag in the fully
152   // qualified name hash to get the same effect.
153   unsigned Hash = hash_combine(Context.getQualifiedNameHash(), Tag, NameRef);
154 
155   // FIXME: dsymutil-classic compatibility: when we don't have a name,
156   // use the filename.
157   if (IsAnonymousNamespace)
158     Hash = hash_combine(Hash, FileRef);
159 
160   // Now look if this context already exists.
161   DeclContext Key(Hash, Line, ByteSize, Tag, NameRef, FileRef, Context);
162   auto ContextIter = Contexts.find(&Key);
163 
164   if (ContextIter == Contexts.end()) {
165     // The context wasn't found.
166     bool Inserted;
167     DeclContext *NewContext =
168         new (Allocator) DeclContext(Hash, Line, ByteSize, Tag, NameRef, FileRef,
169                                     Context, DIE, U.getUniqueID());
170     std::tie(ContextIter, Inserted) = Contexts.insert(NewContext);
171     assert(Inserted && "Failed to insert DeclContext");
172     (void)Inserted;
173   } else if (Tag != dwarf::DW_TAG_namespace &&
174              !(*ContextIter)->setLastSeenDIE(U, DIE)) {
175     // The context was found, but it is ambiguous with another context
176     // in the same file. Mark it invalid.
177     return PointerIntPair<DeclContext *, 1>(*ContextIter, /* IntVal= */ 1);
178   }
179 
180   assert(ContextIter != Contexts.end());
181   // FIXME: dsymutil-classic compatibility. Union types aren't
182   // uniques, but their children might be.
183   if ((Tag == dwarf::DW_TAG_subprogram &&
184        Context.getTag() != dwarf::DW_TAG_structure_type &&
185        Context.getTag() != dwarf::DW_TAG_class_type) ||
186       (Tag == dwarf::DW_TAG_union_type))
187     return PointerIntPair<DeclContext *, 1>(*ContextIter, /* IntVal= */ 1);
188 
189   return PointerIntPair<DeclContext *, 1>(*ContextIter);
190 }
191 
192 StringRef
193 DeclContextTree::getResolvedPath(CompileUnit &CU, unsigned FileNum,
194                                  const DWARFDebugLine::LineTable &LineTable) {
195   std::pair<unsigned, unsigned> Key = {CU.getUniqueID(), FileNum};
196 
197   ResolvedPathsMap::const_iterator It = ResolvedPaths.find(Key);
198   if (It == ResolvedPaths.end()) {
199     std::string FileName;
200     bool FoundFileName = LineTable.getFileNameByIndex(
201         FileNum, CU.getOrigUnit().getCompilationDir(),
202         DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, FileName);
203     (void)FoundFileName;
204     assert(FoundFileName && "Must get file name from line table");
205 
206     // Second level of caching, this time based on the file's parent
207     // path.
208     StringRef ResolvedPath = PathResolver.resolve(FileName, StringPool);
209 
210     It = ResolvedPaths.insert(std::make_pair(Key, ResolvedPath)).first;
211   }
212 
213   return It->second;
214 }
215 
216 } // namespace llvm
217