[ELF2] - Fixed PLT rellocations types for X86 and X86_64 targets

[grimar]

Summary

R_386_JUMP_SLOT and R_X86_64_JUMP_SLOT are used for PLT rellocations for these targets.

[grimar]

more correct variant

[grimar]

Since r249835 reverted "[ELF2] - Implemented rel[a].plt sections" then this one is no more actual now I think.

[ruiu]

LGTM with a nit.

ELF/OutputSections.cpp

172–201

Overall the conditions in this function are getting complicated over time. We need to simplify that. (It's a TODO for me, so this change is okay.)

ELF/Target.cpp

206

Don't have to add fixmes. I'd remove them instead (but not in this patch).

[grimar]

Code relied on changes from http://reviews.llvm.org/D13569 which were reverted in r249835.
So commit is not possible anymore.

ELF/OutputSections.cpp

for (const DynamicReloc<ELFT> &Rel : Relocs) {
     OutputSection<ELFT> *OutSec = C.getOutputSection();
     uint32_t SymIndex = RI.getSymbol(IsMips64EL);
     const ObjectFile<ELFT> &File = *C.getFile();
     const SymbolBody *Body = File.getSymbolBody(SymIndex);
     const ELFFile<ELFT> &Obj = File.getObj();
 
     uint32_t Type = RI.getType(IsMips64EL);
 
     bool CanBePreempted = canBePreempted(Body);
     uintX_t Addend = 0;
     if (!CanBePreempted) {
       if (IsRela) {
         if (Body)
           Addend += getSymVA<ELFT>(cast<ELFSymbolBody<ELFT>>(*Body));
         else
           Addend += getLocalSymVA(
               Obj.getRelocationSymbol(&RI, File.getSymbolTable()), File);
       }
       P->setSymbolAndType(0, Target->getRelativeReloc(), IsMips64EL);
     }
 
     if (Body && Target->relocNeedsGot(Type, *Body)) {
       P->r_offset = Out<ELFT>::Got->getEntryAddr(*Body);
-      if (CanBePreempted)
+      if (CanBePreempted) {
+        bool NeedsPlt = Target->relocNeedsPlt(Type, *Body);
         P->setSymbolAndType(Body->getDynamicSymbolTableIndex(),
-                            Target->getGotReloc(), IsMips64EL);
+                            NeedsPlt ? Target->getPltReloc()
+                                     : Target->getGotReloc(),
+                            IsMips64EL);
+      }
     } else {
       if (IsRela)
         Addend += static_cast<const Elf_Rela &>(RI).r_addend;
       P->r_offset = RI.r_offset + C.getOutputSectionOff() + OutSec->getVA();
       if (CanBePreempted)
         P->setSymbolAndType(Body->getDynamicSymbolTableIndex(), Type,
                             IsMips64EL);
     }
 
     if (IsRela)
       static_cast<Elf_Rela *>(P)->r_addend = Addend;
   }
 }
 
 template <class ELFT> void RelocationSection<ELFT>::finalize() {
   this->Header.sh_link = Out<ELFT>::DynSymTab->getSectionIndex();

ELF/Target.h

 
 class TargetInfo {
 public:
   llvm::StringRef getDefaultEntry() const { return DefaultEntry; }
   unsigned getPageSize() const { return PageSize; }
   uint64_t getVAStart() const { return VAStart; }
   unsigned getPCRelReloc() const { return PCRelReloc; }
   unsigned getGotReloc() const { return GotReloc; }
+  unsigned getPltReloc() const { return PltReloc; }
   unsigned getGotRefReloc() const { return GotRefReloc; }
   unsigned getRelativeReloc() const { return RelativeReloc; }
   unsigned getPltEntrySize() const { return PltEntrySize; }
   virtual void writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                              uint64_t PltEntryAddr) const = 0;
   virtual bool isRelRelative(uint32_t Type) const;
   virtual bool relocNeedsGot(uint32_t Type, const SymbolBody &S) const = 0;
   virtual bool relocPointsToGot(uint32_t Type) const;
   virtual bool relocNeedsPlt(uint32_t Type, const SymbolBody &S) const = 0;
   virtual void relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                            uint64_t BaseAddr, uint64_t SymVA) const = 0;
 
   virtual ~TargetInfo();
 
 protected:
   unsigned PageSize = 4096;
   uint64_t VAStart;
   unsigned PCRelReloc;
   unsigned GotRefReloc;
   unsigned GotReloc;
+  unsigned PltReloc;
   unsigned RelativeReloc;
   unsigned PltEntrySize = 8;
   llvm::StringRef DefaultEntry = "_start";
 };
 
 class X86TargetInfo final : public TargetInfo {
 public:
   X86TargetInfo();

ELF/Target.cpp

 
 bool TargetInfo::relocPointsToGot(uint32_t Type) const { return false; }
 
 bool TargetInfo::isRelRelative(uint32_t Type) const { return true; }
 
 X86TargetInfo::X86TargetInfo() {
   PCRelReloc = R_386_PC32;
   GotReloc = R_386_GLOB_DAT;
+  PltReloc = R_386_JUMP_SLOT;
   GotRefReloc = R_386_GOT32;
   VAStart = 0x10000;
 }
 
 void X86TargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                   uint64_t PltEntryAddr) const {
   // jmpl *val; nop; nop
   const uint8_t Inst[] = {0xff, 0x25, 0, 0, 0, 0, 0x90, 0x90};
default:
     error(Twine("unrecognized reloc ") + Twine(Type));
     break;
   }
 }
 
 X86_64TargetInfo::X86_64TargetInfo() {
   PCRelReloc = R_X86_64_PC32;
   GotReloc = R_X86_64_GLOB_DAT;
+  PltReloc = R_X86_64_JUMP_SLOT;
   GotRefReloc = R_X86_64_PC32;
   RelativeReloc = R_X86_64_RELATIVE;
 
   // On freebsd x86_64 the first page cannot be mmaped.
   // On linux that is controled by vm.mmap_min_addr. At least on some x86_64
   // installs that is 65536, so the first 15 pages cannot be used.
   // Given that, the smallest value that can be used in here is 0x10000.
   // If using 2MB pages, the smallest page aligned address that works is
default:
     error(Twine("unrecognized reloc ") + Twine(Type));
     break;
   }
 }
 
 PPC64TargetInfo::PPC64TargetInfo() {
   // PCRelReloc = FIXME
   // GotReloc = FIXME
+  // PltReloc = FIXME
   PltEntrySize = 32;
   PageSize = 65536;
   VAStart = 0x10000000;
 }
 void PPC64TargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                     uint64_t PltEntryAddr) const {}
 bool PPC64TargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
   return false;
default:
     error(Twine("unrecognized reloc ") + Twine(Type));
     break;
   }
 }
 
 PPCTargetInfo::PPCTargetInfo() {
   // PCRelReloc = FIXME
   // GotReloc = FIXME
+  // PltReloc = FIXME
   PageSize = 65536;
   VAStart = 0x10000000;
 }
 void PPCTargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                   uint64_t PltEntryAddr) const {}
 bool PPCTargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
   return false;
 }
 bool PPCTargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
   return false;
 }
 void PPCTargetInfo::relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                                 uint64_t BaseAddr, uint64_t SymVA) const {}
 
 ARMTargetInfo::ARMTargetInfo() {
   // PCRelReloc = FIXME
   // GotReloc = FIXME
+  // PltReloc = FIXME
   VAStart = 0x8000;
 }
 void ARMTargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                   uint64_t PltEntryAddr) const {}
 bool ARMTargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
   return false;
 }
 bool ARMTargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
   return false;
 }
 void ARMTargetInfo::relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,
                                 uint64_t BaseAddr, uint64_t SymVA) const {}
 
 AArch64TargetInfo::AArch64TargetInfo() {
   // PCRelReloc = FIXME
   // GotReloc = FIXME
+  // PltReloc = FIXME
   VAStart = 0x400000;
 }
 void AArch64TargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                       uint64_t PltEntryAddr) const {}
 bool AArch64TargetInfo::relocNeedsGot(uint32_t Type,
                                       const SymbolBody &S) const {
   return false;
 }
default:
     error(Twine("unrecognized reloc ") + Twine(Type));
     break;
   }
 }
 
 MipsTargetInfo::MipsTargetInfo() {
   // PCRelReloc = FIXME
   // GotReloc = FIXME
+  // PltReloc = FIXME
   DefaultEntry = "__start";
   PageSize = 65536;
   VAStart = 0x400000;
 }
 
 void MipsTargetInfo::writePltEntry(uint8_t *Buf, uint64_t GotEntryAddr,
                                    uint64_t PltEntryAddr) const {}
 

test/elf2/plt-i686.s

 // CHECK-NEXT: Offset:
 // CHECK-NEXT: Size: 16
 // CHECK-NEXT: Link: 0
 // CHECK-NEXT: Info: 0
 // CHECK-NEXT: AddressAlignment: 16
 
 // CHECK:      Relocations [
 // CHECK-NEXT:   Section ({{.*}}) .rel.plt {
-// CHECK-NEXT:     0x13058 R_386_GLOB_DAT bar 0x0
-// CHECK-NEXT:     0x1305C R_386_GLOB_DAT zed 0x0
+// CHECK-NEXT:     0x13058 R_386_JUMP_SLOT bar 0x0
+// CHECK-NEXT:     0x1305C R_386_JUMP_SLOT zed 0x0
 // CHECK-NEXT:   }
 // CHECK-NEXT: ]
 
 // Unfortunately FileCheck can't do math, so we have to check for explicit
 // values:
 
 // 0x12010 - (0x12000 + 1) - 4 = 11
 // 0x12010 - (0x12005 + 1) - 4 = 2

test/elf2/plt.s

 // CHECK-NEXT: Offset:
 // CHECK-NEXT: Size: 24
 // CHECK-NEXT: Link: 0
 // CHECK-NEXT: Info: 0
 // CHECK-NEXT: AddressAlignment: 16
 
 // CHECK:      Relocations [
 // CHECK-NEXT:   Section ({{.*}}) .rela.plt {
-// CHECK-NEXT:     0x30B0 R_X86_64_GLOB_DAT bar 0x0
-// CHECK-NEXT:     0x30B8 R_X86_64_GLOB_DAT zed 0x0
-// CHECK-NEXT:     0x30C0 R_X86_64_GLOB_DAT _start 0x0
+// CHECK-NEXT:     0x30B0 R_X86_64_JUMP_SLOT bar 0x0
+// CHECK-NEXT:     0x30B8 R_X86_64_JUMP_SLOT zed 0x0
+// CHECK-NEXT:     0x30C0 R_X86_64_JUMP_SLOT _start 0x0
 // CHECK-NEXT:   }
 // CHECK-NEXT: ]
 
 // Unfortunately FileCheck can't do math, so we have to check for explicit
 // values:
 
 // 0x12020 - (0x12000 + 1) - 4 = 27
 // 0x12020 - (0x12005 + 1) - 4 = 22