llvm/tools/llvm-jitlink/llvm-jitlink-elf.cpp

   1 //===---- llvm-jitlink-elf.cpp -- ELF parsing support for llvm-jitlink ----===//
   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 // ELF parsing support for llvm-jitlink.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm-jitlink.h"
  14
  15 #include "llvm/Support/Error.h"
  16 #include "llvm/Support/Path.h"
  17
  18 #define DEBUG_TYPE "llvm_jitlink"
  19
  20 using namespace llvm;
  21 using namespace llvm::jitlink;
  22
  23 static bool isELFGOTSection(Section &S) { return S.getName() == "$__GOT"; }
  24
  25 static bool isELFStubsSection(Section &S) { return S.getName() == "$__STUBS"; }
  26
  27 static Expected<Edge &> getFirstRelocationEdge(LinkGraph &G, Block &B) {
  28   auto EItr = std::find_if(B.edges().begin(), B.edges().end(),
  29                            [](Edge &E) { return E.isRelocation(); });
  30   if (EItr == B.edges().end())
  31     return make_error<StringError>("GOT entry in " + G.getName() + ", \"" +
  32                                        B.getSection().getName() +
  33                                        "\" has no relocations",
  34                                    inconvertibleErrorCode());
  35   return *EItr;
  36 }
  37
  38 static Expected<Symbol &> getELFGOTTarget(LinkGraph &G, Block &B) {
  39   auto E = getFirstRelocationEdge(G, B);
  40   if (!E)
  41     return E.takeError();
  42   auto &TargetSym = E->getTarget();
  43   if (!TargetSym.hasName())
  44     return make_error<StringError>(
  45         "GOT entry in " + G.getName() + ", \"" +
  46             TargetSym.getBlock().getSection().getName() +
  47             "\" points to anonymous "
  48             "symbol",
  49         inconvertibleErrorCode());
  50   return TargetSym;
  51 }
  52
  53 static Expected<Symbol &> getELFStubTarget(LinkGraph &G, Block &B) {
  54   auto E = getFirstRelocationEdge(G, B);
  55   if (!E)
  56     return E.takeError();
  57   auto &GOTSym = E->getTarget();
  58   if (!GOTSym.isDefined() || !isELFGOTSection(GOTSym.getBlock().getSection()))
  59     return make_error<StringError>(
  60         "Stubs entry in " + G.getName() + ", \"" +
  61             GOTSym.getBlock().getSection().getName() +
  62             "\" does not point to GOT entry",
  63         inconvertibleErrorCode());
  64   return getELFGOTTarget(G, GOTSym.getBlock());
  65 }
  66
  67 namespace llvm {
  68
  69 Error registerELFGraphInfo(Session &S, LinkGraph &G) {
  70   auto FileName = sys::path::filename(G.getName());
  71   if (S.FileInfos.count(FileName)) {
  72     return make_error<StringError>("When -check is passed, file names must be "
  73                                    "distinct (duplicate: \"" +
  74                                        FileName + "\")",
  75                                    inconvertibleErrorCode());
  76   }
  77
  78   auto &FileInfo = S.FileInfos[FileName];
  79   LLVM_DEBUG({
  80     dbgs() << "Registering ELF file info for \"" << FileName << "\"\n";
  81   });
  82   for (auto &Sec : G.sections()) {
  83     LLVM_DEBUG({
  84       dbgs() << "  Section \"" << Sec.getName() << "\": "
  85              << (llvm::empty(Sec.symbols()) ? "empty. skipping."
  86                                             : "processing...")
  87              << "\n";
  88     });
  89
  90     // Skip empty sections.
  91     if (llvm::empty(Sec.symbols()))
  92       continue;
  93
  94     if (FileInfo.SectionInfos.count(Sec.getName()))
  95       return make_error<StringError>("Encountered duplicate section name \"" +
  96                                          Sec.getName() + "\" in \"" + FileName +
  97                                          "\"",
  98                                      inconvertibleErrorCode());
  99
 100     bool isGOTSection = isELFGOTSection(Sec);
 101     bool isStubsSection = isELFStubsSection(Sec);
 102
 103     bool SectionContainsContent = false;
 104     bool SectionContainsZeroFill = false;
 105
 106     auto *FirstSym = *Sec.symbols().begin();
 107     auto *LastSym = FirstSym;
 108     for (auto *Sym : Sec.symbols()) {
 109       if (Sym->getAddress() < FirstSym->getAddress())
 110         FirstSym = Sym;
 111       if (Sym->getAddress() > LastSym->getAddress())
 112         LastSym = Sym;
 113
 114       if (isGOTSection) {
 115         if (Sym->isSymbolZeroFill())
 116           return make_error<StringError>("zero-fill atom in GOT section",
 117                                          inconvertibleErrorCode());
 118
 119         // If this is a GOT symbol with size (i.e. not the GOT start symbol)
 120         // then add it to the GOT entry info table.
 121         if (Sym->getSize() != 0) {
 122           if (auto TS = getELFGOTTarget(G, Sym->getBlock()))
 123             FileInfo.GOTEntryInfos[TS->getName()] = {
 124                 Sym->getSymbolContent(), Sym->getAddress().getValue()};
 125           else
 126             return TS.takeError();
 127         }
 128         SectionContainsContent = true;
 129       } else if (isStubsSection) {
 130         if (Sym->isSymbolZeroFill())
 131           return make_error<StringError>("zero-fill atom in Stub section",
 132                                          inconvertibleErrorCode());
 133
 134         if (auto TS = getELFStubTarget(G, Sym->getBlock()))
 135           FileInfo.StubInfos[TS->getName()] = {Sym->getSymbolContent(),
 136                                                Sym->getAddress().getValue()};
 137         else
 138           return TS.takeError();
 139         SectionContainsContent = true;
 140       }
 141
 142       if (Sym->hasName()) {
 143         if (Sym->isSymbolZeroFill()) {
 144           S.SymbolInfos[Sym->getName()] = {Sym->getSize(),
 145                                            Sym->getAddress().getValue()};
 146           SectionContainsZeroFill = true;
 147         } else {
 148           S.SymbolInfos[Sym->getName()] = {Sym->getSymbolContent(),
 149                                            Sym->getAddress().getValue()};
 150           SectionContainsContent = true;
 151         }
 152       }
 153     }
 154
 155     auto SecAddr = FirstSym->getAddress();
 156     auto SecSize =
 157         (LastSym->getBlock().getAddress() + LastSym->getBlock().getSize()) -
 158         SecAddr;
 159
 160     if (SectionContainsZeroFill && SectionContainsContent)
 161       return make_error<StringError>("Mixed zero-fill and content sections not "
 162                                      "supported yet",
 163                                      inconvertibleErrorCode());
 164     if (SectionContainsZeroFill)
 165       FileInfo.SectionInfos[Sec.getName()] = {SecSize, SecAddr.getValue()};
 166     else
 167       FileInfo.SectionInfos[Sec.getName()] = {
 168           ArrayRef<char>(FirstSym->getBlock().getContent().data(), SecSize),
 169           SecAddr.getValue()};
 170   }
 171
 172   return Error::success();
 173 }
 174
 175 } // end namespace llvm