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

1 files changed, 61 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
index 7a192b72da9..b7aab91d217 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
@@ -384,6 +384,9 @@ public:
                             const MCInst &Inst) const override;
   bool clearsSuperRegisters(const MCRegisterInfo &MRI, const MCInst &Inst,
                             APInt &Mask) const override;
+  std::vector<std::pair<uint64_t, uint64_t>>
+  findPltEntries(uint64_t PltSectionVA, ArrayRef<uint8_t> PltContents,
+                 uint64_t GotSectionVA, const Triple &TargetTriple) const;
 };
 
 bool X86MCInstrAnalysis::isDependencyBreaking(const MCSubtargetInfo &STI,
@@ -510,6 +513,64 @@ bool X86MCInstrAnalysis::clearsSuperRegisters(const MCRegisterInfo &MRI,
   return Mask.getBoolValue();
 }
 
+static std::vector<std::pair<uint64_t, uint64_t>>
+findX86PltEntries(uint64_t PltSectionVA, ArrayRef<uint8_t> PltContents,
+                  uint64_t GotPltSectionVA) {
+  // Do a lightweight parsing of PLT entries.
+  std::vector<std::pair<uint64_t, uint64_t>> Result;
+  for (uint64_t Byte = 0, End = PltContents.size(); Byte + 6 < End; ) {
+    // Recognize a jmp.
+    if (PltContents[Byte] == 0xff && PltContents[Byte + 1] == 0xa3) {
+      // The jmp instruction at the beginning of each PLT entry jumps to the
+      // address of the base of the .got.plt section plus the immediate.
+      uint32_t Imm = support::endian::read32le(PltContents.data() + Byte + 2);
+      Result.push_back(
+          std::make_pair(PltSectionVA + Byte, GotPltSectionVA + Imm));
+      Byte += 6;
+    } else if (PltContents[Byte] == 0xff && PltContents[Byte + 1] == 0x25) {
+      // The jmp instruction at the beginning of each PLT entry jumps to the
+      // immediate.
+      uint32_t Imm = support::endian::read32le(PltContents.data() + Byte + 2);
+      Result.push_back(std::make_pair(PltSectionVA + Byte, Imm));
+      Byte += 6;
+    } else
+      Byte++;
+  }
+  return Result;
+}
+
+static std::vector<std::pair<uint64_t, uint64_t>>
+findX86_64PltEntries(uint64_t PltSectionVA, ArrayRef<uint8_t> PltContents) {
+  // Do a lightweight parsing of PLT entries.
+  std::vector<std::pair<uint64_t, uint64_t>> Result;
+  for (uint64_t Byte = 0, End = PltContents.size(); Byte + 6 < End; ) {
+    // Recognize a jmp.
+    if (PltContents[Byte] == 0xff && PltContents[Byte + 1] == 0x25) {
+      // The jmp instruction at the beginning of each PLT entry jumps to the
+      // address of the next instruction plus the immediate.
+      uint32_t Imm = support::endian::read32le(PltContents.data() + Byte + 2);
+      Result.push_back(
+          std::make_pair(PltSectionVA + Byte, PltSectionVA + Byte + 6 + Imm));
+      Byte += 6;
+    } else
+      Byte++;
+  }
+  return Result;
+}
+
+std::vector<std::pair<uint64_t, uint64_t>> X86MCInstrAnalysis::findPltEntries(
+    uint64_t PltSectionVA, ArrayRef<uint8_t> PltContents,
+    uint64_t GotPltSectionVA, const Triple &TargetTriple) const {
+  switch (TargetTriple.getArch()) {
+    case Triple::x86:
+      return findX86PltEntries(PltSectionVA, PltContents, GotPltSectionVA);
+    case Triple::x86_64:
+      return findX86_64PltEntries(PltSectionVA, PltContents);
+    default:
+      return {};
+  }
+}
+
 } // end of namespace X86_MC
 
 } // end of namespace llvm