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> DeclContextTree::getChildDeclContext(
44     DeclContext &Context, const DWARFDie &DIE, CompileUnit &U,
45     UniquingStringPool &StringPool, 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   const char *Name = DIE.getName(DINameKind::LinkageName);
84   const char *ShortName = DIE.getName(DINameKind::ShortName);
85   StringRef NameRef;
86   StringRef ShortNameRef;
87   StringRef FileRef;
88 
89   if (Name)
90     NameRef = StringPool.internString(Name);
91   else if (Tag == dwarf::DW_TAG_namespace)
92     // FIXME: For dsymutil-classic compatibility. I think uniquing within
93     // anonymous namespaces is wrong. There is no ODR guarantee there.
94     NameRef = StringPool.internString("(anonymous namespace)");
95 
96   if (ShortName && ShortName != Name)
97     ShortNameRef = StringPool.internString(ShortName);
98   else
99     ShortNameRef = NameRef;
100 
101   if (Tag != dwarf::DW_TAG_class_type && Tag != dwarf::DW_TAG_structure_type &&
102       Tag != dwarf::DW_TAG_union_type &&
103       Tag != dwarf::DW_TAG_enumeration_type && NameRef.empty())
104     return PointerIntPair<DeclContext *, 1>(nullptr);
105 
106   unsigned Line = 0;
107   unsigned ByteSize = std::numeric_limits<uint32_t>::max();
108 
109   if (!InClangModule) {
110     // Gather some discriminating data about the DeclContext we will be
111     // creating: File, line number and byte size. This shouldn't be necessary,
112     // because the ODR is just about names, but given that we do some
113     // approximations with overloaded functions and anonymous namespaces, use
114     // these additional data points to make the process safer.
115     //
116     // This is disabled for clang modules, because forward declarations of
117     // module-defined types do not have a file and line.
118     ByteSize = dwarf::toUnsigned(DIE.find(dwarf::DW_AT_byte_size),
119                                  std::numeric_limits<uint64_t>::max());
120     if (Tag != dwarf::DW_TAG_namespace || !Name) {
121       if (unsigned FileNum =
122               dwarf::toUnsigned(DIE.find(dwarf::DW_AT_decl_file), 0)) {
123         if (const auto *LT = U.getOrigUnit().getContext().getLineTableForUnit(
124                 &U.getOrigUnit())) {
125           // FIXME: dsymutil-classic compatibility. I'd rather not
126           // unique anything in anonymous namespaces, but if we do, then
127           // verify that the file and line correspond.
128           if (!Name && Tag == dwarf::DW_TAG_namespace)
129             FileNum = 1;
130 
131           if (LT->hasFileAtIndex(FileNum)) {
132             Line = dwarf::toUnsigned(DIE.find(dwarf::DW_AT_decl_line), 0);
133             // Cache the resolved paths based on the index in the line table,
134             // because calling realpath is expansive.
135             StringRef ResolvedPath = U.getResolvedPath(FileNum);
136             if (!ResolvedPath.empty()) {
137               FileRef = ResolvedPath;
138             } else {
139               std::string File;
140               bool FoundFileName = LT->getFileNameByIndex(
141                   FileNum, U.getOrigUnit().getCompilationDir(),
142                   DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath,
143                   File);
144               (void)FoundFileName;
145               assert(FoundFileName && "Must get file name from line table");
146               // Second level of caching, this time based on the file's parent
147               // path.
148               FileRef = PathResolver.resolve(File, StringPool);
149               U.setResolvedPath(FileNum, FileRef);
150             }
151           }
152         }
153       }
154     }
155   }
156 
157   if (!Line && NameRef.empty())
158     return PointerIntPair<DeclContext *, 1>(nullptr);
159 
160   // We hash NameRef, which is the mangled name, in order to get most
161   // overloaded functions resolve correctly.
162   //
163   // Strictly speaking, hashing the Tag is only necessary for a
164   // DW_TAG_module, to prevent uniquing of a module and a namespace
165   // with the same name.
166   //
167   // FIXME: dsymutil-classic won't unique the same type presented
168   // once as a struct and once as a class. Using the Tag in the fully
169   // qualified name hash to get the same effect.
170   unsigned Hash = hash_combine(Context.getQualifiedNameHash(), Tag, NameRef);
171 
172   // FIXME: dsymutil-classic compatibility: when we don't have a name,
173   // use the filename.
174   if (Tag == dwarf::DW_TAG_namespace && NameRef == "(anonymous namespace)")
175     Hash = hash_combine(Hash, FileRef);
176 
177   // Now look if this context already exists.
178   DeclContext Key(Hash, Line, ByteSize, Tag, NameRef, FileRef, Context);
179   auto ContextIter = Contexts.find(&Key);
180 
181   if (ContextIter == Contexts.end()) {
182     // The context wasn't found.
183     bool Inserted;
184     DeclContext *NewContext =
185         new (Allocator) DeclContext(Hash, Line, ByteSize, Tag, NameRef, FileRef,
186                                     Context, DIE, U.getUniqueID());
187     std::tie(ContextIter, Inserted) = Contexts.insert(NewContext);
188     assert(Inserted && "Failed to insert DeclContext");
189     (void)Inserted;
190   } else if (Tag != dwarf::DW_TAG_namespace &&
191              !(*ContextIter)->setLastSeenDIE(U, DIE)) {
192     // The context was found, but it is ambiguous with another context
193     // in the same file. Mark it invalid.
194     return PointerIntPair<DeclContext *, 1>(*ContextIter, /* Invalid= */ 1);
195   }
196 
197   assert(ContextIter != Contexts.end());
198   // FIXME: dsymutil-classic compatibility. Union types aren't
199   // uniques, but their children might be.
200   if ((Tag == dwarf::DW_TAG_subprogram &&
201        Context.getTag() != dwarf::DW_TAG_structure_type &&
202        Context.getTag() != dwarf::DW_TAG_class_type) ||
203       (Tag == dwarf::DW_TAG_union_type))
204     return PointerIntPair<DeclContext *, 1>(*ContextIter, /* Invalid= */ 1);
205 
206   return PointerIntPair<DeclContext *, 1>(*ContextIter);
207 }
208 
209 } // namespace llvm
210