Commit e9b9a1d3 authored by Fangrui Song's avatar Fangrui Song
Browse files

[ELF] Move demoteSymbols to Writer.cpp. NFC 

History of demoteSharedSymbols:

* https://reviews.llvm.org/D45536 demotes SharedSymbol
* https://reviews.llvm.org/D111365 demotes lazy symbols
* The pending #69295 will demote symbols defined in discarded sections

The pass is placed after markLive just to be clear that it needs `isNeeded`
information computed by markLive. The remaining passes in Driver.cpp do not use
symbol information. Move the pass to Writer.cpp to be closer to other
symbol-related passes.
parent d4088e7d

lld/ELF/Driver.cpp

+0 −19
Original line number Diff line number Diff line
@@ -2248,24 +2248,6 @@ static void replaceCommonSymbols() { 
  }

}



// If all references to a DSO happen to be weak, the DSO is not added to

// DT_NEEDED. If that happens, replace ShardSymbol with Undefined to avoid

// dangling references to an unneeded DSO. Use a weak binding to avoid

// --no-allow-shlib-undefined diagnostics. Similarly, demote lazy symbols.

static void demoteSharedAndLazySymbols() {

  llvm::TimeTraceScope timeScope("Demote shared and lazy symbols");

  for (Symbol *sym : symtab.getSymbols()) {

    auto *s = dyn_cast<SharedSymbol>(sym);

    if (!(s && !cast<SharedFile>(s->file)->isNeeded) && !sym->isLazy())

      continue;



    uint8_t binding = sym->isLazy() ? sym->binding : uint8_t(STB_WEAK);

    Undefined(nullptr, sym->getName(), binding, sym->stOther, sym->type)

        .overwrite(*sym);

    sym->versionId = VER_NDX_GLOBAL;

  }

}



// The section referred to by `s` is considered address-significant. Set the

// keepUnique flag on the section if appropriate.

static void markAddrsig(Symbol *s) {
@@ -3023,7 +3005,6 @@ void LinkerDriver::link(opt::InputArgList &args) { 


  // Garbage collection and removal of shared symbols from unused shared objects.

  invokeELFT(markLive,);

  demoteSharedAndLazySymbols();



  // Make copies of any input sections that need to be copied into each

  // partition.

lld/ELF/Writer.cpp

+23 −5
Original line number Diff line number Diff line
@@ -251,6 +251,23 @@ void elf::addReservedSymbols() { 
  ElfSym::edata2 = add("_edata", -1);

}



// If all references to a DSO happen to be weak, the DSO is not added to

// DT_NEEDED. If that happens, replace ShardSymbol with Undefined to avoid

// dangling references to an unneeded DSO. Use a weak binding to avoid

// --no-allow-shlib-undefined diagnostics. Similarly, demote lazy symbols.

static void demoteSymbols() {

  llvm::TimeTraceScope timeScope("Demote symbols");

  for (Symbol *sym : symtab.getSymbols()) {

    auto *s = dyn_cast<SharedSymbol>(sym);

    if (!(s && !cast<SharedFile>(s->file)->isNeeded) && !sym->isLazy())

      continue;

    uint8_t binding = sym->isLazy() ? sym->binding : uint8_t(STB_WEAK);

    Undefined(nullptr, sym->getName(), binding, sym->stOther, sym->type)

        .overwrite(*sym);

    sym->versionId = VER_NDX_GLOBAL;

  }

}



// Fully static executables don't support MTE globals at this point in time, as

// we currently rely on:

//   - A dynamic loader to process relocations, and
@@ -1935,13 +1952,14 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() { 
      for (Partition &part : partitions)

        finalizeSynthetic(part.ehFrame.get());

    }

  }



  demoteSymbols();

  if (config->hasDynSymTab) {

    parallelForEach(symtab.getSymbols(), [](Symbol *sym) {

      sym->isPreemptible = computeIsPreemptible(*sym);

    });

  }

  }



  // Change values of linker-script-defined symbols from placeholders (assigned

  // by declareSymbols) to actual definitions.