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