[ELF2] Make sure symbol-less relocations make it to the target's handler

[hfinkel]

Summary

Some relocations don't actually require a symbol. For example, PPC64 as a TOC relocation (R_PPC64_TOC) which just bases its value on the location of the TOC base, and so there does not seem to be any corresponding symbol. Make sure the target's handler can see such relocations.

[ruiu]

LGTM with nits

ELF/InputSection.cpp

39

uintX_t SymVA = 0;

46–53

// getRelocationSymbol may return a null for some relocations such as R_PPC64_TOC.
if (const Elf_Sym *Sym = File.getObj().getRelocationSymbol(&RI, SymTab))
  SymVA = getLocalSymVA(Sym, File);

[hfinkel]

The code change here has been rendered unnecessary by r250095; the test-case fixup was committed in r250104.

ELF/InputSection.cpp

void InputSection<ELFT>::relocate(
     uint8_t *Buf, iterator_range<const Elf_Rel_Impl<ELFT, isRela> *> Rels,
     const ObjectFile<ELFT> &File, uintX_t BaseAddr) {
   typedef Elf_Rel_Impl<ELFT, isRela> RelType;
   bool IsMips64EL = File.getObj().isMips64EL();
   for (const RelType &RI : Rels) {
     uint32_t SymIndex = RI.getSymbol(IsMips64EL);
     uint32_t Type = RI.getType(IsMips64EL);
     uintX_t GotVA = Out<ELFT>::Got->getVA();
     uintX_t SymVA;
 
     // Handle relocations for local symbols -- they never get
     // resolved so we don't allocate a SymbolBody.
     const Elf_Shdr *SymTab = File.getSymbolTable();
     if (SymIndex < SymTab->sh_info) {
       const Elf_Sym *Sym = File.getObj().getRelocationSymbol(&RI, SymTab);
-      if (!Sym)
-        continue;
+      if (!Sym) {
+        // Some targets have special relocations that don't correspond to
+        // particular symbols (for example, R_PPC64_TOC). SymVA is unused for
+        // these.
+        SymVA = 0;
+      } else {
         SymVA = getLocalSymVA(Sym, File);
+      }
     } else {
       SymbolBody &Body = *File.getSymbolBody(SymIndex);
       SymVA = getSymVA<ELFT>(Body);
       if (Target->relocNeedsPlt(Type, Body)) {
         SymVA = Out<ELFT>::Plt->getEntryAddr(Body);
         Type = Target->getPCRelReloc();
       } else if (Target->relocNeedsGot(Type, Body)) {
         SymVA = Out<ELFT>::Got->getEntryAddr(Body);

test/elf2/basic64be.s

 # CHECK-NEXT:     Address: 0x10020000
 # CHECK-NEXT:     Offset: 0x2000
 # CHECK-NEXT:     Size: 24
 # CHECK-NEXT:     Link: 0
 # CHECK-NEXT:     Info: 0
 # CHECK-NEXT:     AddressAlignment: 1
 # CHECK-NEXT:     EntrySize: 0
 # CHECK-NEXT:     SectionData (
-# CHECK-NEXT:      0000: 00000000 10010000 00000000 00000000  |................|
+# FIXME: The TOC pointer here is not calculated correctly because this input
+# has no .got section (it has no .toc or .tocbss either, so we should use the
+# .plt address to form the TOC base value).
+# CHECK-NEXT:      0000: 00000000 10010000 FFFFFFFF FFFF8000  |................|
 # CHECK-NEXT:      0010: 00000000 00000000                    |........|
 # CHECK-NEXT:     )
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Section {
 # CHECK-NEXT:     Index: 4
 # CHECK-NEXT:     Name: .bss
 # CHECK-NEXT:     Type: SHT_NOBITS (0x8)
 # CHECK-NEXT:     Flags [ (0x3)