lld

// lld/ELF/Driver.cpp

// Do actual linking. Note that when this function is called,
// all linker scripts have already been parsed.
template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
  ...

   // Now that we have a complete list of input files.
  // Beyond this point, no new files are added.
  // Aggregate all input sections into one place.
  for (InputFile *f : objectFiles)
    for (InputSectionBase *s : f->getSections()){
      if (s && s != &InputSection::discarded){
        inputSections.push_back(s);
        MSGLL("input section added: '" + s->name 
              + "', size: " + std::to_string(s->getSize()) + "\n");
      }else{
        if (s) MSGLL("empty section disgarded: '" + s->name + "'\n");
      }
    }
  for (BinaryFile *f : binaryFiles)
    for (InputSectionBase *s : f->getSections())
      inputSections.push_back(cast<InputSection>(s));

  llvm::erase_if(inputSections, [](InputSectionBase *s) {
    if (s->type == SHT_LLVM_SYMPART) {
      readSymbolPartitionSection<ELFT>(s);
      MSGLL("input section '" + s->name + "' removed\n");
      return true;
    }

    // We do not want to emit debug sections if --strip-all
    // or -strip-debug are given.
    if(config->strip != StripPolicy::None &&
           (s->name.startswith(".debug") || s->name.startswith(".zdebug")))
    {
      MSGLL("input section (debug) '" + s->name + "' removed\n");
      return true;
    }else{
      return false;
    }
  });


  // Linker scripts control how input sections are assigned to output sections.
  // Input sections that were not handled by scripts are called "orphans", and
  // they are assigned to output sections by the default rule. Process that.
  script->addOrphanSections();

  ...
}

// Add sections that didn't match any sections command.
void LinkerScript::addOrphanSections() {
  StringMap<TinyPtrVector<OutputSection *>> map;
  std::vector<OutputSection *> v;

  auto add = [&](InputSectionBase *s) {
    MSGLL("Handling Orphan Section: " + s->name + "\n");
    if (!s->isLive() || s->parent)
      return;

    StringRef name = getOutputSectionName(s);

    MSGLL("Orphan section is placed in '" + name + "'\n");

    if (config->orphanHandling == OrphanHandlingPolicy::Error)
      error(toString(s) + " is being placed in '" + name + "'");
    else if (config->orphanHandling == OrphanHandlingPolicy::Warn)
      warn(toString(s) + " is being placed in '" + name + "'");

    if (OutputSection *sec = findByName(sectionCommands, name)) {
      sec->addSection(cast<InputSection>(s));
      return;
    }

    if (OutputSection *os = addInputSec(map, s, name))
      v.push_back(os);
    assert(s->getOutputSection()->sectionIndex == UINT32_MAX);
  };

  // For futher --emit-reloc handling code we need target output section
  // to be created before we create relocation output section, so we want
  // to create target sections first. We do not want priority handling
  // for synthetic sections because them are special.
  for (InputSectionBase *isec : inputSections) {
    if (auto *sec = dyn_cast<InputSection>(isec))
      if (InputSectionBase *rel = sec->getRelocatedSection())
        if (auto *relIS = dyn_cast_or_null<InputSectionBase>(rel->parent))
          add(relIS);
    add(isec);
  }

  // If no SECTIONS command was given, we should insert sections commands
  // before others, so that we can handle scripts which refers them,
  // for example: "foo = ABSOLUTE(ADDR(.text)));".
  // When SECTIONS command is present we just add all orphans to the end.
  if (hasSectionsCommand)
    sectionCommands.insert(sectionCommands.end(), v.begin(), v.end());
  else
    sectionCommands.insert(sectionCommands.begin(), v.begin(), v.end());
}