[ELF] - fix possible UB when dereferencing null

[grimar]

Summary

In InputSection.cpp it was possible to dereference null.
Had to change signature of relocateTlsOptimize to accept pointer instead of reference.

[grimar]

ELF/InputSection.cpp

174

Thats the place. Having nullptr is ok here.

[ruiu]

LGTM

ELF/InputSection.cpp

for (size_t I = 0; I < Num; ++I) {
     const Elf_Shdr *SymTab = File->getSymbolTable();
     SymbolBody *Body = nullptr;
     if (SymIndex >= SymTab->sh_info)
       Body = File->getSymbolBody(SymIndex)->repl();
 
     if (Target->isTlsOptimized(Type, Body)) {
       uintX_t SymVA;
       if (!Body)
         SymVA = getLocalRelTarget(*File, RI, 0);
       else if (Target->relocNeedsGot(Type, *Body))
         SymVA = Out<ELFT>::Got->getEntryAddr(*Body);
       else
         SymVA = getSymVA<ELFT>(*Body);
       // By optimizing TLS relocations, it is sometimes needed to skip
       // relocations that immediately follow TLS relocations. This function
       // knows how many slots we need to skip.
       I += Target->relocateTlsOptimize(BufLoc, BufEnd, Type, AddrLoc, SymVA,
-                                       *Body);
+                                       Body);
       continue;
     }
 
     // Handle relocations for local symbols -- they never get
     // resolved so we don't allocate a SymbolBody.
     uintX_t A = getAddend<ELFT>(RI);
     if (!Body) {
       uintX_t SymVA = getLocalRelTarget(*File, RI, A);

ELF/Target.h

public:
   virtual void relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type,
                            uint64_t P, uint64_t SA, uint64_t ZA = 0,
                            uint8_t *PairedLoc = nullptr) const = 0;
   virtual bool isGotRelative(uint32_t Type) const;
   virtual bool isTlsOptimized(unsigned Type, const SymbolBody *S) const;
   virtual bool needsCopyRel(uint32_t Type, const SymbolBody &S) const;
   virtual unsigned relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd,
                                        uint32_t Type, uint64_t P, uint64_t SA,
-                                       const SymbolBody &S) const;
+                                       const SymbolBody *S) const;
   virtual ~TargetInfo();
 
 protected:
   unsigned PageSize = 4096;
 
   // 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.

ELF/Target.cpp

public:
   bool relocNeedsGot(uint32_t Type, const SymbolBody &S) const override;
   bool relocNeedsPlt(uint32_t Type, const SymbolBody &S) const override;
   void relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type, uint64_t P,
                    uint64_t SA, uint64_t ZA = 0,
                    uint8_t *PairedLoc = nullptr) const override;
   bool isTlsOptimized(unsigned Type, const SymbolBody *S) const override;
   unsigned relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type,
                                uint64_t P, uint64_t SA,
-                               const SymbolBody &S) const override;
+                               const SymbolBody *S) const override;
   bool isGotRelative(uint32_t Type) const override;
 
 private:
   void relocateTlsLdToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
                          uint64_t SA) const;
   void relocateTlsGdToIe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
                          uint64_t SA) const;
   void relocateTlsGdToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
public:
   void relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type, uint64_t P,
                    uint64_t SA, uint64_t ZA = 0,
                    uint8_t *PairedLoc = nullptr) const override;
   bool isRelRelative(uint32_t Type) const override;
   bool isTlsOptimized(unsigned Type, const SymbolBody *S) const override;
   bool isSizeReloc(uint32_t Type) const override;
   unsigned relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type,
                                uint64_t P, uint64_t SA,
-                               const SymbolBody &S) const override;
+                               const SymbolBody *S) const override;
 
 private:
   void relocateTlsLdToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
                          uint64_t SA) const;
   void relocateTlsGdToLe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
                          uint64_t SA) const;
   void relocateTlsGdToIe(uint8_t *Loc, uint8_t *BufEnd, uint64_t P,
                          uint64_t SA) const;

 bool TargetInfo::isHintReloc(uint32_t Type) const { return false; }
 
 bool TargetInfo::isRelRelative(uint32_t Type) const { return true; }
 
 bool TargetInfo::isSizeReloc(uint32_t Type) const { return false; }
 
 unsigned TargetInfo::relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd,
                                          uint32_t Type, uint64_t P, uint64_t SA,
-                                         const SymbolBody &S) const {
+                                         const SymbolBody *S) const {
   return 0;
 }
 
 void TargetInfo::writeGotHeaderEntries(uint8_t *Buf) const {}
 
 void TargetInfo::writeGotPltHeaderEntries(uint8_t *Buf) const {}
 
 X86TargetInfo::X86TargetInfo() {

 
 bool X86TargetInfo::relocNeedsDynRelative(unsigned Type) const {
   return Config->Shared && Type == R_386_TLS_IE;
 }
 
 unsigned X86TargetInfo::relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd,
                                             uint32_t Type, uint64_t P,
                                             uint64_t SA,
-                                            const SymbolBody &S) const {
+                                            const SymbolBody *S) const {
   switch (Type) {
   case R_386_TLS_GD:
-    if (canBePreempted(&S, true))
+    if (canBePreempted(S, true))
       relocateTlsGdToIe(Loc, BufEnd, P, SA);
     else
       relocateTlsGdToLe(Loc, BufEnd, P, SA);
     // The next relocation should be against __tls_get_addr, so skip it
     return 1;
   case R_386_TLS_GOTIE:
   case R_386_TLS_IE:
     relocateTlsIeToLe(Type, Loc, BufEnd, P, SA);

 // This function applies a TLS relocation with an optimization as described
 // in the Ulrich's document. As a result of rewriting instructions at the
 // relocation target, relocations immediately follow the TLS relocation (which
 // would be applied to rewritten instructions) may have to be skipped.
 // This function returns a number of relocations that need to be skipped.
 unsigned X86_64TargetInfo::relocateTlsOptimize(uint8_t *Loc, uint8_t *BufEnd,
                                                uint32_t Type, uint64_t P,
                                                uint64_t SA,
-                                               const SymbolBody &S) const {
+                                               const SymbolBody *S) const {
   switch (Type) {
   case R_X86_64_DTPOFF32:
     relocateOne(Loc, BufEnd, R_X86_64_TPOFF32, P, SA);
     return 0;
   case R_X86_64_GOTTPOFF:
     relocateTlsIeToLe(Loc, BufEnd, P, SA);
     return 0;
   case R_X86_64_TLSGD: {
-    if (canBePreempted(&S, true))
+    if (canBePreempted(S, true))
       relocateTlsGdToIe(Loc, BufEnd, P, SA);
     else
       relocateTlsGdToLe(Loc, BufEnd, P, SA);
     // The next relocation should be against __tls_get_addr, so skip it
     return 1;
   }
   case R_X86_64_TLSLD:
     relocateTlsLdToLe(Loc, BufEnd, P, SA);