From d36fb48a274bd6c53ce289e968be4c53c189e0a7 Mon Sep 17 00:00:00 2001
From: Joel Galenson <jgalenson@google.com>
Date: Fri, 24 Aug 2018 15:21:56 +0000
Subject: Find PLT entries for x86, x86_64, and AArch64.

This adds a new method to ELFObjectFileBase that returns the symbols and addresses of PLT entries.

This design was suggested by pcc and eugenis in https://reviews.llvm.org/D49383.

Differential Revision: https://reviews.llvm.org/D50203

llvm-svn: 340610
---
 llvm/lib/Object/ELFObjectFile.cpp | 65 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

(limited to 'llvm/lib/Object/ELFObjectFile.cpp')

diff --git a/llvm/lib/Object/ELFObjectFile.cpp b/llvm/lib/Object/ELFObjectFile.cpp
index e806c8f..173cb30 100644
--- a/llvm/lib/Object/ELFObjectFile.cpp
+++ b/llvm/lib/Object/ELFObjectFile.cpp
@@ -14,6 +14,7 @@
 #include "llvm/Object/ELFObjectFile.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/MC/MCInstrAnalysis.h"
 #include "llvm/MC/SubtargetFeature.h"
 #include "llvm/Object/ELF.h"
 #include "llvm/Object/ELFTypes.h"
@@ -23,6 +24,7 @@
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/TargetRegistry.h"
 #include <algorithm>
 #include <cstddef>
 #include <cstdint>
@@ -327,3 +329,66 @@ void ELFObjectFileBase::setARMSubArch(Triple &TheTriple) const {
 
   TheTriple.setArchName(Triple);
 }
+
+std::vector<std::pair<DataRefImpl, uint64_t>>
+ELFObjectFileBase::getPltAddresses() const {
+  std::string Err;
+  const auto Triple = makeTriple();
+  const auto *T = TargetRegistry::lookupTarget(Triple.str(), Err);
+  if (!T)
+    return {};
+  uint64_t JumpSlotReloc = 0;
+  switch (Triple.getArch()) {
+    case Triple::x86:
+      JumpSlotReloc = ELF::R_386_JUMP_SLOT;
+      break;
+    case Triple::x86_64:
+      JumpSlotReloc = ELF::R_X86_64_JUMP_SLOT;
+      break;
+    case Triple::aarch64:
+      JumpSlotReloc = ELF::R_AARCH64_JUMP_SLOT;
+      break;
+    default:
+      return {};
+  }
+  const auto *MIA = T->createMCInstrAnalysis(T->createMCInstrInfo());
+  if (!MIA)
+    return {};
+  Optional<SectionRef> Plt = None, RelaPlt = None, GotPlt = None;
+  for (const SectionRef &Section : sections()) {
+    StringRef Name;
+    if (Section.getName(Name))
+      continue;
+    if (Name == ".plt")
+      Plt = Section;
+    else if (Name == ".rela.plt" || Name == ".rel.plt")
+      RelaPlt = Section;
+    else if (Name == ".got.plt")
+      GotPlt = Section;
+  }
+  if (!Plt || !RelaPlt || !GotPlt)
+    return {};
+  StringRef PltContents;
+  if (Plt->getContents(PltContents))
+    return {};
+  ArrayRef<uint8_t> PltBytes((const uint8_t *)PltContents.data(),
+                             Plt->getSize());
+  auto PltEntries = MIA->findPltEntries(Plt->getAddress(), PltBytes,
+                                        GotPlt->getAddress(), Triple);
+  // Build a map from GOT entry virtual address to PLT entry virtual address.
+  DenseMap<uint64_t, uint64_t> GotToPlt;
+  for (const auto &Entry : PltEntries)
+    GotToPlt.insert(std::make_pair(Entry.second, Entry.first));
+  // Find the relocations in the dynamic relocation table that point to
+  // locations in the GOT for which we know the corresponding PLT entry.
+  std::vector<std::pair<DataRefImpl, uint64_t>> Result;
+  for (const auto &Relocation : RelaPlt->relocations()) {
+    if (Relocation.getType() != JumpSlotReloc)
+      continue;
+    auto PltEntryIter = GotToPlt.find(Relocation.getOffset());
+    if (PltEntryIter != GotToPlt.end())
+      Result.push_back(std::make_pair(
+          Relocation.getSymbol()->getRawDataRefImpl(), PltEntryIter->second));
+  }
+  return Result;
+}
-- 
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