[ELF] Remove error-prone RelocationBaseSection::classof

Author: MaskRay

lld/ELF/OutputSections.cpp

@@ -882,7 +882,11 @@ void OutputSection::checkDynRelAddends(Ctx &ctx) {
     // for input .rel[a].<sec> sections which we simply pass through to the
     // output. We skip over those and only look at the synthetic relocation
     // sections created during linking.
-    const auto *sec = dyn_cast<RelocationBaseSection>(sections[i]);
+    if (!SyntheticSection::classof(sections[i]) ||
+        !is_contained({ELF::SHT_REL, ELF::SHT_RELA, ELF::SHT_RELR},
+                      sections[i]->type))
+      return;
+    const auto *sec = cast<RelocationBaseSection>(sections[i]);
     if (!sec)
       return;
     for (const DynamicReloc &rel : sec->relocs) {

lld/ELF/SyntheticSections.h

@@ -547,13 +547,7 @@ class RelocationBaseSection : public SyntheticSection {
   void mergeRels();
   void partitionRels();
   void finalizeContents() override;
-  static bool classof(const SectionBase *d) {
-    return SyntheticSection::classof(d) &&
-           (d->type == llvm::ELF::SHT_RELA || d->type == llvm::ELF::SHT_REL ||
-            d->type == llvm::ELF::SHT_RELR ||
-            (d->type == llvm::ELF::SHT_AARCH64_AUTH_RELR &&
-             elf::ctx.arg.emachine == llvm::ELF::EM_AARCH64));
-  }
+
   int32_t dynamicTag, sizeDynamicTag;
   SmallVector<DynamicReloc, 0> relocs;
 

lld/ELF/Writer.cpp

@@ -1690,10 +1690,9 @@ static void removeUnusedSyntheticSections(Ctx &ctx) {
         // finalizeAddressDependentContent, making .rela.dyn no longer empty.
         // Conservatively keep .rela.dyn. .relr.auth.dyn can be made empty, but
         // we would fail to remove it here.
-        if (ctx.arg.emachine == EM_AARCH64 && ctx.arg.relrPackDynRelocs)
-          if (auto *relSec = dyn_cast<RelocationBaseSection>(sec))
-            if (relSec == ctx.mainPart->relaDyn.get())
-              return false;
+        if (ctx.arg.emachine == EM_AARCH64 && ctx.arg.relrPackDynRelocs &&
+            sec == ctx.mainPart->relaDyn.get())
+          return false;
         unused.insert(sec);
         return true;
       });