[llvm-objcopy] Fill .symtab_shndx section correctly

Differential revision: https://reviews.llvm.org/D60555

llvm-svn: 358278

llvm/test/tools/llvm-objcopy/ELF/many-sections.test

@@ -3,6 +3,7 @@ RUN: llvm-objcopy %t %t2
 RUN: llvm-readobj --file-headers %t2 | FileCheck --check-prefix=EHDR %s
 RUN: llvm-readobj --sections %t2 | FileCheck --check-prefix=SECS %s
 RUN: llvm-readobj --symbols %t2 | grep "Symbol {" | wc -l | FileCheck --check-prefix=SYMS %s
+RUN: llvm-readobj -symbols %t2 | FileCheck %s --check-prefix=SYM_SEC_IDS
 
 EHDR:      Format: ELF64-x86-64
 EHDR-NEXT: Arch: x86_64
@@ -51,3 +52,52 @@ SECS-NEXT: AddressAlignment: 4
 SECS-NEXT: EntrySize: 4
 SECS: Index: 65287
 SYMS: 65284
+
+SYM_SEC_IDS:         Section: s9 (0xFEFF)
+SYM_SEC_IDS-NEXT:  }
+SYM_SEC_IDS-NEXT:  Symbol {
+SYM_SEC_IDS-NEXT:    Name: s9 (37)
+SYM_SEC_IDS-NEXT:    Value: 0x0
+SYM_SEC_IDS-NEXT:    Size: 0
+SYM_SEC_IDS-NEXT:    Binding: Local (0x0)
+SYM_SEC_IDS-NEXT:    Type: None (0x0)
+SYM_SEC_IDS-NEXT:    Other: 0
+SYM_SEC_IDS-NEXT:    Section: s9 (0xFF01)
+SYM_SEC_IDS-NEXT:  }
+SYM_SEC_IDS-NEXT:  Symbol {
+SYM_SEC_IDS-NEXT:    Name: s9 (37)
+SYM_SEC_IDS-NEXT:    Value: 0x0
+SYM_SEC_IDS-NEXT:    Size: 0
+SYM_SEC_IDS-NEXT:    Binding: Local (0x0)
+SYM_SEC_IDS-NEXT:    Type: None (0x0)
+SYM_SEC_IDS-NEXT:    Other: 0
+SYM_SEC_IDS-NEXT:    Section: s9 (0xFF00)
+SYM_SEC_IDS-NEXT:  }
+SYM_SEC_IDS-NEXT:  Symbol {
+SYM_SEC_IDS-NEXT:    Name: s9 (37)
+SYM_SEC_IDS-NEXT:    Value: 0x0
+SYM_SEC_IDS-NEXT:    Size: 0
+SYM_SEC_IDS-NEXT:    Binding: Local (0x0)
+SYM_SEC_IDS-NEXT:    Type: None (0x0)
+SYM_SEC_IDS-NEXT:    Other: 0
+SYM_SEC_IDS-NEXT:    Section: s9 (0x1982)
+SYM_SEC_IDS-NEXT:  }
+SYM_SEC_IDS-NEXT:  Symbol {
+SYM_SEC_IDS-NEXT:    Name: s9 (37)
+SYM_SEC_IDS-NEXT:    Value: 0x0
+SYM_SEC_IDS-NEXT:    Size: 0
+SYM_SEC_IDS-NEXT:    Binding: Local (0x0)
+SYM_SEC_IDS-NEXT:    Type: None (0x0)
+SYM_SEC_IDS-NEXT:    Other: 0
+SYM_SEC_IDS-NEXT:    Section: s9 (0xFF03)
+SYM_SEC_IDS-NEXT:  }
+SYM_SEC_IDS-NEXT:  Symbol {
+SYM_SEC_IDS-NEXT:    Name: s9 (37)
+SYM_SEC_IDS-NEXT:    Value: 0x0
+SYM_SEC_IDS-NEXT:    Size: 0
+SYM_SEC_IDS-NEXT:    Binding: Local (0x0)
+SYM_SEC_IDS-NEXT:    Type: None (0x0)
+SYM_SEC_IDS-NEXT:    Other: 0
+SYM_SEC_IDS-NEXT:    Section: s9 (0xFF04)
+SYM_SEC_IDS-NEXT:  }
+

llvm/tools/llvm-objcopy/ELF/Object.cpp

@@ -486,22 +486,30 @@ void SymbolTableSection::finalize() {
 }
 
 void SymbolTableSection::prepareForLayout() {
-  // Add all potential section indexes before file layout so that the section
-  // index section has the approprite size.
-  if (SectionIndexTable != nullptr) {
-    for (const auto &Sym : Symbols) {
-      if (Sym->DefinedIn != nullptr && Sym->DefinedIn->Index >= SHN_LORESERVE)
-        SectionIndexTable->addIndex(Sym->DefinedIn->Index);
-      else
-        SectionIndexTable->addIndex(SHN_UNDEF);
-    }
-  }
+  // Reserve proper amount of space in section index table, so we can
+  // layout sections correctly. We will fill the table with correct
+  // indexes later in fillShdnxTable.
+  if (SectionIndexTable)  
+    SectionIndexTable->reserve(Symbols.size());
   // Add all of our strings to SymbolNames so that SymbolNames has the right
   // size before layout is decided.
   for (auto &Sym : Symbols)
     SymbolNames->addString(Sym->Name);
 }
 
+void SymbolTableSection::fillShndxTable() {
+  if (SectionIndexTable == nullptr)
+    return;
+  // Fill section index table with real section indexes. This function must
+  // be called after assignOffsets.
+  for (const auto &Sym : Symbols) {
+    if (Sym->DefinedIn != nullptr && Sym->DefinedIn->Index >= SHN_LORESERVE)
+      SectionIndexTable->addIndex(Sym->DefinedIn->Index);
+    else
+      SectionIndexTable->addIndex(SHN_UNDEF);
+  }
+}
+
 const Symbol *SymbolTableSection::getSymbolByIndex(uint32_t Index) const {
   if (Symbols.size() <= Index)
     error("Invalid symbol index: " + Twine(Index));
@@ -1661,6 +1669,11 @@ template <class ELFT> Error ELFWriter<ELFT>::finalize() {
 
   assignOffsets();
 
+  // layoutSections could have modified section indexes, so we need
+  // to fill the index table after assignOffsets.
+  if (Obj.SymbolTable != nullptr)
+    Obj.SymbolTable->fillShndxTable();
+
   // Finally now that all offsets and indexes have been set we can finalize any
   // remaining issues.
   uint64_t Offset = Obj.SHOffset + sizeof(Elf_Shdr);

llvm/tools/llvm-objcopy/ELF/Object.h

@@ -481,9 +481,14 @@ private:
 public:
   virtual ~SectionIndexSection() {}
   void addIndex(uint32_t Index) {
-    Indexes.push_back(Index);
-    Size += 4;
+    assert(Size > 0);
+    Indexes.push_back(Index);    
   }
+
+  void reserve(size_t NumSymbols) {
+    Indexes.reserve(NumSymbols);
+    Size = NumSymbols * 4;
+  }  
   void setSymTab(SymbolTableSection *SymTab) { Symbols = SymTab; }
   void initialize(SectionTableRef SecTable) override;
   void finalize() override;
@@ -524,6 +529,7 @@ public:
     SectionIndexTable = ShndxTable;
   }
   const SectionIndexSection *getShndxTable() const { return SectionIndexTable; }
+  void fillShndxTable();
   const SectionBase *getStrTab() const { return SymbolNames; }
   const Symbol *getSymbolByIndex(uint32_t Index) const;
   Symbol *getSymbolByIndex(uint32_t Index);