1 //===--- DebugInfoSupport.cpp -- Utils for debug info support ---*- 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 // Utilities to preserve and parse debug info from LinkGraphs.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/ExecutionEngine/Orc/Debugging/DebugInfoSupport.h"
14 
15 #include "llvm/Support/SmallVectorMemoryBuffer.h"
16 
17 #define DEBUG_TYPE "orc"
18 
19 using namespace llvm;
20 using namespace llvm::orc;
21 using namespace llvm::jitlink;
22 
23 namespace {
24 static DenseSet<StringRef> DWARFSectionNames = {
25 #define HANDLE_DWARF_SECTION(ENUM_NAME, ELF_NAME, CMDLINE_NAME, OPTION)        \
26   StringRef(ELF_NAME),
27 #include "llvm/BinaryFormat/Dwarf.def"
28 #undef HANDLE_DWARF_SECTION
29 };
30 
31 // We might be able to drop relocations to symbols that do end up
32 // being pruned by the linker, but for now we just preserve all
33 static void preserveDWARFSection(LinkGraph &G, Section &Sec) {
34   DenseMap<Block *, Symbol *> Preserved;
35   for (auto Sym : Sec.symbols()) {
36     if (Sym->isLive())
37       Preserved[&Sym->getBlock()] = Sym;
38     else if (!Preserved.count(&Sym->getBlock()))
39       Preserved[&Sym->getBlock()] = Sym;
40   }
41   for (auto Block : Sec.blocks()) {
42     auto &PSym = Preserved[Block];
43     if (!PSym)
44       PSym = &G.addAnonymousSymbol(*Block, 0, 0, false, true);
45     else if (!PSym->isLive())
46       PSym->setLive(true);
47   }
48 }
49 
50 static SmallVector<char, 0> getSectionData(Section &Sec) {
51   SmallVector<char, 0> SecData;
52   SmallVector<Block *, 8> SecBlocks(Sec.blocks().begin(), Sec.blocks().end());
53   std::sort(SecBlocks.begin(), SecBlocks.end(), [](Block *LHS, Block *RHS) {
54     return LHS->getAddress() < RHS->getAddress();
55   });
56   // Convert back to what object file would have, one blob of section content
57   // Assumes all zerofill
58   // TODO handle alignment?
59   // TODO handle alignment offset?
60   for (auto *Block : SecBlocks) {
61     if (Block->isZeroFill())
62       SecData.resize(SecData.size() + Block->getSize(), 0);
63     else
64       SecData.append(Block->getContent().begin(), Block->getContent().end());
65   }
66   return SecData;
67 }
68 
69 static void dumpDWARFContext(DWARFContext &DC) {
70   auto options = llvm::DIDumpOptions();
71   options.DumpType &= ~DIDT_UUID;
72   options.DumpType &= ~(1 << DIDT_ID_DebugFrame);
73   LLVM_DEBUG(DC.dump(dbgs(), options));
74 }
75 
76 } // namespace
77 
78 Error llvm::orc::preserveDebugSections(LinkGraph &G) {
79   if (!G.getTargetTriple().isOSBinFormatELF()) {
80     return make_error<StringError>(
81         "preserveDebugSections only supports ELF LinkGraphs!",
82         inconvertibleErrorCode());
83   }
84   for (auto &Sec : G.sections()) {
85     if (DWARFSectionNames.count(Sec.getName())) {
86       LLVM_DEBUG(dbgs() << "Preserving DWARF section " << Sec.getName()
87                         << "\n");
88       preserveDWARFSection(G, Sec);
89     }
90   }
91   return Error::success();
92 }
93 
94 Expected<std::pair<std::unique_ptr<DWARFContext>,
95                    StringMap<std::unique_ptr<MemoryBuffer>>>>
96 llvm::orc::createDWARFContext(LinkGraph &G) {
97   if (!G.getTargetTriple().isOSBinFormatELF()) {
98     return make_error<StringError>(
99         "createDWARFContext only supports ELF LinkGraphs!",
100         inconvertibleErrorCode());
101   }
102   StringMap<std::unique_ptr<MemoryBuffer>> DWARFSectionData;
103   for (auto &Sec : G.sections()) {
104     if (DWARFSectionNames.count(Sec.getName())) {
105       auto SecData = getSectionData(Sec);
106       auto Name = Sec.getName();
107       // DWARFContext expects the section name to not start with a dot
108       Name.consume_front(".");
109       LLVM_DEBUG(dbgs() << "Creating DWARFContext section " << Name
110                         << " with size " << SecData.size() << "\n");
111       DWARFSectionData[Name] =
112           std::make_unique<SmallVectorMemoryBuffer>(std::move(SecData));
113     }
114   }
115   auto Ctx =
116       DWARFContext::create(DWARFSectionData, G.getPointerSize(),
117                            G.getEndianness() == llvm::endianness::little);
118   dumpDWARFContext(*Ctx);
119   return std::make_pair(std::move(Ctx), std::move(DWARFSectionData));
120 }
121