[ELF] Do not join input sections when linker creates relocatable object file (-r option)

[evgeny777]

Summary

When -r option is used lld may end up creating malformed object file. The simplest example is an input file having following sections

.text._init SHT_PROGBITS
.text._fini SHT_PROGBITS
.rela.text._init SHT_RELA
.rela.text._fini SHT_RELA

Given input above lld will produce object file with two relocation sections for a single section .text. If you then pass this file as an input for GNU ld, you'll get error 'File not recognized: bad value'

[ruiu]

LGTM

ELF/Writer.cpp

94 ↗

(On Diff #73456)

Please replace Name with S->Name in this function. I think it made sense when it was S->getName() but not anymore.

lld/trunk/ELF/LinkerScript.cpp

 
 template <class ELFT>
 void LinkerScript<ELFT>::createSections(OutputSectionFactory<ELFT> &Factory) {
   processCommands(Factory);
   // Add orphan sections.
   for (ObjectFile<ELFT> *F : Symtab<ELFT>::X->getObjectFiles())
     for (InputSectionBase<ELFT> *S : F->getSections())
       if (!isDiscarded(S) && !S->OutSec)
-        addSection(Factory, S, getOutputSectionName(S));
+        addSection(Factory, S, getOutputSectionName(S->Name));
 }
 
 // Sets value of a section-defined symbol. Two kinds of
 // symbols are processed: synthetic symbols, whose value
 // is an offset from beginning of section and regular
 // symbols whose value is absolute.
 template <class ELFT>
 static void assignSectionSymbol(SymbolAssignment *Cmd,

lld/trunk/ELF/Writer.h

struct PhdrEntry {
   void add(OutputSectionBase<ELFT> *Sec);
 
   typename ELFT::Phdr H = {};
   OutputSectionBase<ELFT> *First = nullptr;
   OutputSectionBase<ELFT> *Last = nullptr;
   bool HasLMA = false;
 };
 
-template <class ELFT>
-llvm::StringRef getOutputSectionName(InputSectionBase<ELFT> *S);
+llvm::StringRef getOutputSectionName(llvm::StringRef Name);
 
 template <class ELFT> void reportDiscarded(InputSectionBase<ELFT> *IS);
 
 template <class ELFT> uint32_t getMipsEFlags();
 
 uint8_t getMipsFpAbiFlag(uint8_t OldFlag, uint8_t NewFlag,
                          llvm::StringRef FileName);
 }
 }
 
 #endif

lld/trunk/ELF/Writer.cpp

private:
 
   std::vector<Phdr> Phdrs;
 
   uintX_t FileSize;
   uintX_t SectionHeaderOff;
 };
 } // anonymous namespace
 
-template <class ELFT>
-StringRef elf::getOutputSectionName(InputSectionBase<ELFT> *S) {
-  StringRef Name = S->Name;
+StringRef elf::getOutputSectionName(StringRef Name) {
+  if (Config->Relocatable)
+    return Name;
+
   for (StringRef V :
        {".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.",
         ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
         ".gcc_except_table.", ".tdata.", ".ARM.exidx."}) {
     StringRef Prefix = V.drop_back();
     if (Name.startswith(V) || Name == Prefix)
       return Prefix;
   }
template <class ELFT> void Writer<ELFT>::createSections() {
   for (elf::ObjectFile<ELFT> *F : Symtab<ELFT>::X->getObjectFiles()) {
     for (InputSectionBase<ELFT> *IS : F->getSections()) {
       if (isDiscarded(IS)) {
         reportDiscarded(IS);
         continue;
       }
       OutputSectionBase<ELFT> *Sec;
       bool IsNew;
-      std::tie(Sec, IsNew) = Factory.create(IS, getOutputSectionName(IS));
+      std::tie(Sec, IsNew) = Factory.create(IS, getOutputSectionName(IS->Name));
       if (IsNew)
         OutputSections.push_back(Sec);
       Sec->addSection(IS);
     }
   }
 
   sortInitFini(findSection(".init_array"));
   sortInitFini(findSection(".fini_array"));

 template struct elf::PhdrEntry<ELF64LE>;
 template struct elf::PhdrEntry<ELF64BE>;
 
 template bool elf::isRelroSection<ELF32LE>(OutputSectionBase<ELF32LE> *);
 template bool elf::isRelroSection<ELF32BE>(OutputSectionBase<ELF32BE> *);
 template bool elf::isRelroSection<ELF64LE>(OutputSectionBase<ELF64LE> *);
 template bool elf::isRelroSection<ELF64BE>(OutputSectionBase<ELF64BE> *);
 
-template StringRef elf::getOutputSectionName<ELF32LE>(InputSectionBase<ELF32LE> *);
-template StringRef elf::getOutputSectionName<ELF32BE>(InputSectionBase<ELF32BE> *);
-template StringRef elf::getOutputSectionName<ELF64LE>(InputSectionBase<ELF64LE> *);
-template StringRef elf::getOutputSectionName<ELF64BE>(InputSectionBase<ELF64BE> *);
-
 template void elf::reportDiscarded<ELF32LE>(InputSectionBase<ELF32LE> *);
 template void elf::reportDiscarded<ELF32BE>(InputSectionBase<ELF32BE> *);
 template void elf::reportDiscarded<ELF64LE>(InputSectionBase<ELF64LE> *);
 template void elf::reportDiscarded<ELF64BE>(InputSectionBase<ELF64BE> *);

lld/trunk/test/ELF/relocatable-sections.s

+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
+# RUN: ld.lld -r %t1.o -o %t
+# RUN: llvm-objdump -section-headers %t | FileCheck %s
+
+# CHECK:      .text
+# CHECK-NEXT: .text._init
+# CHECK-NEXT: .text._fini
+# CHECK-NEXT: .rela.text     
+# CHECK-NEXT: .rela.text._init
+# CHECK-NEXT: .rela.text._fini
+
+.globl _start
+_start:
+ call foo
+ nop
+
+.section .xxx,"a"
+ .quad 0
+
+.section .text._init,"ax"
+ .quad .xxx
+foo:
+ call bar
+ nop
+
+
+.section .text._fini,"ax"
+ .quad .xxx
+bar:
+ nop