[PATCH] D20028: Delete dead code. Document live code.

[Rafael Ávila de Espíndola via llvm-commits]

rafael created this revision.
rafael added a reviewer: ruiu.
rafael added a subscriber: llvm-commits.

The first .got.plt entries are used by the first plt entry to support lazy loading. With that deleted I can run programs with LD_BIND_NOW, but not without.

The value of the first entry does seem unused. I can boostrap and run all tests with this.


http://reviews.llvm.org/D20028

Files:
  ELF/OutputSections.cpp
  ELF/Target.cpp
  ELF/Target.h

Index: ELF/Target.h
===================================================================
--- ELF/Target.h
+++ ELF/Target.h
@@ -28,7 +28,6 @@
   virtual bool isTlsLocalDynamicRel(uint32_t Type) const;
   virtual bool isTlsGlobalDynamicRel(uint32_t Type) const;
   virtual uint32_t getDynRel(uint32_t Type) const { return Type; }
-  virtual void writeGotPltHeader(uint8_t *Buf) const {}
   virtual void writeGotPlt(uint8_t *Buf, uint64_t Plt) const {};
   virtual uint64_t getImplicitAddend(const uint8_t *Buf, uint32_t Type) const;
 
@@ -78,7 +77,11 @@
   uint32_t TlsOffsetRel;
   unsigned PltEntrySize = 8;
   unsigned PltZeroSize = 0;
+
+  // At least on x86_64 positions 1 and 2 are used by the first plt entry
+  // to support lazy loading. Position 0 seems unused.
   unsigned GotPltHeaderEntriesNum = 3;
+
   uint32_t ThunkSize = 0;
   bool UseLazyBinding = false;
 
Index: ELF/Target.cpp
===================================================================
--- ELF/Target.cpp
+++ ELF/Target.cpp
@@ -81,7 +81,6 @@
   X86TargetInfo();
   RelExpr getRelExpr(uint32_t Type, const SymbolBody &S) const override;
   uint64_t getImplicitAddend(const uint8_t *Buf, uint32_t Type) const override;
-  void writeGotPltHeader(uint8_t *Buf) const override;
   uint32_t getDynRel(uint32_t Type) const override;
   bool isTlsLocalDynamicRel(uint32_t Type) const override;
   bool isTlsGlobalDynamicRel(uint32_t Type) const override;
@@ -106,7 +105,6 @@
   bool isTlsLocalDynamicRel(uint32_t Type) const override;
   bool isTlsGlobalDynamicRel(uint32_t Type) const override;
   bool isTlsInitialExecRel(uint32_t Type) const override;
-  void writeGotPltHeader(uint8_t *Buf) const override;
   void writeGotPlt(uint8_t *Buf, uint64_t Plt) const override;
   void writePltZero(uint8_t *Buf) const override;
   void writePlt(uint8_t *Buf, uint64_t GotEntryAddr, uint64_t PltEntryAddr,
@@ -298,10 +296,6 @@
   }
 }
 
-void X86TargetInfo::writeGotPltHeader(uint8_t *Buf) const {
-  write32le(Buf, Out<ELF32LE>::Dynamic->getVA());
-}
-
 void X86TargetInfo::writeGotPlt(uint8_t *Buf, uint64_t Plt) const {
   // Entries in .got.plt initially points back to the corresponding
   // PLT entries with a fixed offset to skip the first instruction.
@@ -530,10 +524,6 @@
   }
 }
 
-void X86_64TargetInfo::writeGotPltHeader(uint8_t *Buf) const {
-  write64le(Buf, Out<ELF64LE>::Dynamic->getVA());
-}
-
 void X86_64TargetInfo::writeGotPlt(uint8_t *Buf, uint64_t Plt) const {
   // See comments in X86TargetInfo::writeGotPlt.
   write32le(Buf, Plt + 6);
Index: ELF/OutputSections.cpp
===================================================================
--- ELF/OutputSections.cpp
+++ ELF/OutputSections.cpp
@@ -75,7 +75,6 @@
 }
 
 template <class ELFT> void GotPltSection<ELFT>::writeTo(uint8_t *Buf) {
-  Target->writeGotPltHeader(Buf);
   Buf += Target->GotPltHeaderEntriesNum * sizeof(uintX_t);
   for (const SymbolBody *B : Entries) {
     Target->writeGotPlt(Buf, B->getPltVA<ELFT>());


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