[NFCI][ELF] Introduce explicit Computed state for DynamicReloc

lld/ELF/Config.h

@@ -701,6 +701,8 @@ struct Ctx : CommonLinkerContext {
   std::unique_ptr<llvm::TarWriter> tar;
   // InputFile for linker created symbols with no source location.
   InputFile *internalFile = nullptr;
+  // Dummy Undefined for relocations without a symbol.
+  Undefined *dummySym = nullptr;
   // True if symbols can be exported (isExported) or preemptible.
   bool hasDynsym = false;
   // True if SHT_LLVM_SYMPART is used.

lld/ELF/Driver.cpp

@@ -3138,6 +3138,7 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
     ctx.symtab->insert(arg->getValue())->traced = true;
 
   ctx.internalFile = createInternalFile(ctx, "<internal>");
+  ctx.dummySym = make<Undefined>(ctx.internalFile, "", STB_LOCAL, 0, 0);
 
   // Handle -u/--undefined before input files. If both a.a and b.so define foo,
   // -u foo a.a b.so will extract a.a.

lld/ELF/Relocations.cpp

@@ -1948,13 +1948,12 @@ void elf::postScanRelocations(Ctx &ctx) {
 
   GotSection *got = ctx.in.got.get();
   if (ctx.needsTlsLd.load(std::memory_order_relaxed) && got->addTlsIndex()) {
-    static Undefined dummy(ctx.internalFile, "", STB_LOCAL, 0, 0);
     if (ctx.arg.shared)
       ctx.mainPart->relaDyn->addReloc(
           {ctx.target->tlsModuleIndexRel, got, got->getTlsIndexOff()});
     else
       got->addConstant({R_ADDEND, ctx.target->symbolicRel,
-                        got->getTlsIndexOff(), 1, &dummy});
+                        got->getTlsIndexOff(), 1, ctx.dummySym});
   }
 
   assert(ctx.symAux.size() == 1);

lld/ELF/SyntheticSections.cpp

@@ -1647,6 +1647,8 @@ uint64_t DynamicReloc::getOffset() const {
 
 int64_t DynamicReloc::computeAddend(Ctx &ctx) const {
   switch (kind) {
+  case Computed:
+    llvm_unreachable("addend already computed");
   case AddendOnly:
     assert(sym == nullptr);
     return addend;
@@ -1748,7 +1750,7 @@ void DynamicReloc::computeRaw(Ctx &ctx, SymbolTableBaseSection *symt) {
   r_offset = getOffset();
   r_sym = getSymIndex(symt);
   addend = computeAddend(ctx);
-  kind = AddendOnly; // Catch errors
+  kind = Computed; // Catch errors
 }
 
 void RelocationBaseSection::computeRels() {

lld/ELF/SyntheticSections.h

@@ -419,6 +419,9 @@ class StringTableSection final : public SyntheticSection {
 class DynamicReloc {
 public:
   enum Kind {
+    /// The resulting dynamic relocation has already had its addend computed.
+    /// Calling computeAddend() is an error. Only for internal use.
+    Computed,
     /// The resulting dynamic relocation does not reference a symbol (#sym must
     /// be nullptr) and uses #addend as the result of computeAddend(ctx).
     AddendOnly,
@@ -461,6 +464,7 @@ class DynamicReloc {
   uint64_t getOffset() const;
   uint32_t getSymIndex(SymbolTableBaseSection *symTab) const;
   bool needsDynSymIndex() const {
+    assert(kind != Computed && "cannot check kind after computeRaw");
     return kind == AgainstSymbol || kind == AgainstSymbolWithTargetVA;
   }
 

lld/ELF/Target.cpp

@@ -105,10 +105,9 @@ ErrorPlace elf::getErrorPlace(Ctx &ctx, const uint8_t *loc) {
     if (isecLoc <= loc && loc < isecLoc + isec->getSize()) {
       std::string objLoc = isec->getLocation(loc - isecLoc);
       // Return object file location and source file location.
-      Undefined dummy(ctx.internalFile, "", STB_LOCAL, 0, 0);
       ELFSyncStream msg(ctx, DiagLevel::None);
       if (isec->file)
-        msg << isec->getSrcMsg(dummy, loc - isecLoc);
+        msg << isec->getSrcMsg(*ctx.dummySym, loc - isecLoc);
       return {isec, objLoc + ": ", std::string(msg.str())};
     }
   }