2 files changed, 21 insertions, 18 deletions

diff --git a/llvm/tools/llvm-objcopy/Object.cpp b/llvm/tools/llvm-objcopy/Object.cpp
index bb79e4269d4..2bd3aa16f0b 100644
--- a/llvm/tools/llvm-objcopy/Object.cpp
+++ b/llvm/tools/llvm-objcopy/Object.cpp
@@ -289,11 +289,14 @@ bool SectionWithStrTab::classof(const SectionBase *S) {
 }
 
 void SectionWithStrTab::initialize(SectionTableRef SecTable) {
-  setStrTab(SecTable.getSectionOfType<StringTableSection>(
-      Link,
-      "Link field value " + Twine(Link) + " in section " + Name + " is invalid",
-      "Link field value " + Twine(Link) + " in section " + Name +
-          " is not a string table"));
+  auto StrTab = SecTable.getSection(Link,
+                                    "Link field value " + Twine(Link) +
+                                        " in section " + Name + " is invalid");
+  if (StrTab->Type != SHT_STRTAB) {
+    error("Link field value " + Twine(Link) + " in section " + Name +
+          " is not a string table");
+  }
+  setStrTab(StrTab);
 }
 
 void SectionWithStrTab::finalize() { this->Link = StrTab->Index; }
@@ -535,15 +538,6 @@ SectionTableRef Object<ELFT>::readSectionHeaders(const ELFFile<ELFT> &ElfFile) {
         initRelocations(RelSec, SymbolTable,
                         unwrapOrError(ElfFile.relas(Shdr)));
     }
-
-    if (auto Sec = dyn_cast<SectionWithStrTab>(Section.get())) {
-      Sec->setStrTab(SecTable.getSectionOfType<StringTableSection>(
-          Sec->Link,
-          "Link field value " + Twine(Sec->Link) + " in section " + Sec->Name +
-              " is invalid",
-          "Link field value " + Twine(Sec->Link) + " in section " + Sec->Name +
-              " is not a string table"));
-    }
   }
 
   return SecTable;
@@ -621,7 +615,7 @@ void Object<ELFT>::writeSectionHeaders(FileOutputBuffer &Out) const {
 template <class ELFT>
 void Object<ELFT>::writeSectionData(FileOutputBuffer &Out) const {
   for (auto &Section : Sections)
-    Section->writeSection(Out);
+      Section->writeSection(Out);
 }
 
 template <class ELFT>
diff --git a/llvm/tools/llvm-objcopy/Object.h b/llvm/tools/llvm-objcopy/Object.h
index 3def0930a94..391465db65e 100644
--- a/llvm/tools/llvm-objcopy/Object.h
+++ b/llvm/tools/llvm-objcopy/Object.h
@@ -114,7 +114,14 @@ public:
   void writeSection(llvm::FileOutputBuffer &Out) const override;
 };
 
-// This is just a wraper around a StringTableBuilder that implements SectionBase
+// There are two types of string tables that can exist, dynamic and not dynamic.
+// In the dynamic case the string table is allocated. Changing a dynamic string
+// table would mean altering virtual addresses and thus the memory image. So
+// dynamic string tables should not have an interface to modify them or
+// reconstruct them. This type lets us reconstruct a string table. To avoid
+// this class being used for dynamic string tables (which has happened) the
+// classof method checks that the particular instance is not allocated. This
+// then agrees with the makeSection method used to construct most sections.
 class StringTableSection : public SectionBase {
 private:
   llvm::StringTableBuilder StrTabBuilder;
@@ -129,6 +136,8 @@ public:
   void finalize() override;
   void writeSection(llvm::FileOutputBuffer &Out) const override;
   static bool classof(const SectionBase *S) {
+    if (S->Flags & llvm::ELF::SHF_ALLOC)
+      return false;
     return S->Type == llvm::ELF::SHT_STRTAB;
   }
 };
@@ -259,11 +268,11 @@ public:
 
 class SectionWithStrTab : public Section {
 private:
-  StringTableSection *StrTab = nullptr;
+  const SectionBase *StrTab = nullptr;
 
 public:
   SectionWithStrTab(llvm::ArrayRef<uint8_t> Data) : Section(Data) {}
-  void setStrTab(StringTableSection *StringTable) { StrTab = StringTable; }
+  void setStrTab(const SectionBase *StringTable) { StrTab = StringTable; }
   void removeSectionReferences(const SectionBase *Sec) override;
   void initialize(SectionTableRef SecTable) override;
   void finalize() override;