Move writeTo to OutputSectionCommand.

This reduces how many times we have to map from OutputSection to
OutputSectionCommand. It is a required step to moving
clearOutputSections earlier.

In order to always use writeTo in OutputSectionCommand we have to call
fabricateDefaultCommands for -r links and move section compression
after it.

llvm-svn: 303784

lld/ELF/LinkerScript.cpp

@@ -20,6 +20,8 @@
 #include "SymbolTable.h"
 #include "Symbols.h"
 #include "SyntheticSections.h"
+#include "Target.h"
+#include "Threads.h"
 #include "Writer.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
@@ -198,6 +200,15 @@ bool OutputSectionCommand::classof(const BaseCommand *C) {
   return C->Kind == OutputSectionKind;
 }
 
+// Fill [Buf, Buf + Size) with Filler.
+// This is used for linker script "=fillexp" command.
+static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
+  size_t I = 0;
+  for (; I + 4 < Size; I += 4)
+    memcpy(Buf + I, &Filler, 4);
+  memcpy(Buf + I, &Filler, Size - I);
+}
+
 bool InputSectionDescription::classof(const BaseCommand *C) {
   return C->Kind == InputSectionKind;
 }
@@ -1032,10 +1043,12 @@ OutputSectionCommand *LinkerScript::getCmd(OutputSection *Sec) const {
   return I->second;
 }
 
-Optional<uint32_t> LinkerScript::getFiller(OutputSection *Sec) {
+uint32_t OutputSectionCommand::getFiller() {
-  if (OutputSectionCommand *Cmd = getCmd(Sec))
+  if (Filler)
-    return Cmd->Filler;
+    return *Filler;
-  return None;
+  if (Sec->Flags & SHF_EXECINSTR)
+    return Target->TrapInstr;
+  return 0;
 }
 
 static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
@@ -1051,9 +1064,43 @@ static void writeInt(uint8_t *Buf, uint64_t Data, uint64_t Size) {
     llvm_unreachable("unsupported Size argument");
 }
 
-void LinkerScript::writeDataBytes(OutputSection *Sec, uint8_t *Buf) {
+template <class ELFT> void OutputSectionCommand::writeTo(uint8_t *Buf) {
-  if (OutputSectionCommand *Cmd = getCmd(Sec))
+  Sec->Loc = Buf;
-    for (BaseCommand *Base : Cmd->Commands)
+
+  // We may have already rendered compressed content when using
+  // -compress-debug-sections option. Write it together with header.
+  if (!Sec->CompressedData.empty()) {
+    memcpy(Buf, Sec->ZDebugHeader.data(), Sec->ZDebugHeader.size());
+    memcpy(Buf + Sec->ZDebugHeader.size(), Sec->CompressedData.data(),
+           Sec->CompressedData.size());
+    return;
+  }
+
+  // Write leading padding.
+  ArrayRef<InputSection *> Sections = Sec->Sections;
+  uint32_t Filler = getFiller();
+  if (Filler)
+    fill(Buf, Sections.empty() ? Sec->Size : Sections[0]->OutSecOff, Filler);
+
+  parallelForEachN(0, Sections.size(), [=](size_t I) {
+    InputSection *IS = Sections[I];
+    IS->writeTo<ELFT>(Buf);
+
+    // Fill gaps between sections.
+    if (Filler) {
+      uint8_t *Start = Buf + IS->OutSecOff + IS->getSize();
+      uint8_t *End;
+      if (I + 1 == Sections.size())
+        End = Buf + Sec->Size;
+      else
+        End = Buf + Sections[I + 1]->OutSecOff;
+      fill(Start, End - Start, Filler);
+    }
+  });
+
+  // Linker scripts may have BYTE()-family commands with which you
+  // can write arbitrary bytes to the output. Process them if any.
+  for (BaseCommand *Base : Commands)
     if (auto *Data = dyn_cast<BytesDataCommand>(Base))
       writeInt(Buf + Data->Offset, Data->Expression().getValue(), Data->Size);
 }
@@ -1102,3 +1149,8 @@ size_t LinkerScript::getPhdrIndex(const Twine &Loc, StringRef PhdrName) {
   error(Loc + ": section header '" + PhdrName + "' is not listed in PHDRS");
   return 0;
 }
+
+template void OutputSectionCommand::writeTo<ELF32LE>(uint8_t *Buf);
+template void OutputSectionCommand::writeTo<ELF32BE>(uint8_t *Buf);
+template void OutputSectionCommand::writeTo<ELF64LE>(uint8_t *Buf);
+template void OutputSectionCommand::writeTo<ELF64BE>(uint8_t *Buf);

lld/ELF/LinkerScript.h

@@ -130,6 +130,9 @@ struct OutputSectionCommand : BaseCommand {
   ConstraintKind Constraint = ConstraintKind::NoConstraint;
   std::string Location;
   std::string MemoryRegionName;
+
+  template <class ELFT> void writeTo(uint8_t *Buf);
+  uint32_t getFiller();
 };
 
 // This struct represents one section match pattern in SECTIONS() command.
@@ -213,7 +216,6 @@ struct ScriptConfiguration {
 
 class LinkerScript final {
   llvm::DenseMap<OutputSection *, OutputSectionCommand *> SecToCommand;
-  OutputSectionCommand *getCmd(OutputSection *Sec) const;
   void assignSymbol(SymbolAssignment *Cmd, bool InSec);
   void setDot(Expr E, const Twine &Loc, bool InSec);
 
@@ -244,6 +246,7 @@ class LinkerScript final {
   MemoryRegion *CurMemRegion = nullptr;
 
 public:
+  OutputSectionCommand *getCmd(OutputSection *Sec) const;
   bool hasPhdrsCommands() { return !Opt.PhdrsCommands.empty(); }
   uint64_t getDot() { return Dot; }
   OutputSection *getOutputSection(const Twine &Loc, StringRef S);
@@ -263,7 +266,6 @@ public:
   std::vector<PhdrEntry> createPhdrs();
   bool ignoreInterpSection();
 
-  llvm::Optional<uint32_t> getFiller(OutputSection *Sec);
   bool hasLMA(OutputSection *Sec);
   bool shouldKeep(InputSectionBase *S);
   void assignOffsets(OutputSectionCommand *Cmd);
@@ -272,7 +274,6 @@ public:
   void synchronize();
   void assignAddresses(std::vector<PhdrEntry> &Phdrs);
 
-  void writeDataBytes(OutputSection *Sec, uint8_t *Buf);
   void addSymbol(SymbolAssignment *Cmd);
   void processCommands(OutputSectionFactory &Factory);
 

lld/ELF/OutputSections.cpp

@@ -103,7 +103,7 @@ template <class ELFT> void OutputSection::maybeCompress() {
 
   // Write section contents to a temporary buffer and compress it.
   std::vector<uint8_t> Buf(Size);
-  writeTo<ELFT>(Buf.data());
+  Script->getCmd(this)->writeTo<ELFT>(Buf.data());
   if (Error E = zlib::compress(toStringRef(Buf), CompressedData))
     fatal("compress failed: " + llvm::toString(std::move(E)));
 
@@ -259,65 +259,6 @@ void OutputSection::sortCtorsDtors() {
   std::stable_sort(Sections.begin(), Sections.end(), compCtors);
 }
 
-// Fill [Buf, Buf + Size) with Filler.
-// This is used for linker script "=fillexp" command.
-static void fill(uint8_t *Buf, size_t Size, uint32_t Filler) {
-  size_t I = 0;
-  for (; I + 4 < Size; I += 4)
-    memcpy(Buf + I, &Filler, 4);
-  memcpy(Buf + I, &Filler, Size - I);
-}
-
-uint32_t OutputSection::getFiller() {
-  // Determine what to fill gaps between InputSections with, as specified by the
-  // linker script. If nothing is specified and this is an executable section,
-  // fall back to trap instructions to prevent bad diassembly and detect invalid
-  // jumps to padding.
-  if (Optional<uint32_t> Filler = Script->getFiller(this))
-    return *Filler;
-  if (Flags & SHF_EXECINSTR)
-    return Target->TrapInstr;
-  return 0;
-}
-
-template <class ELFT> void OutputSection::writeTo(uint8_t *Buf) {
-  Loc = Buf;
-
-  // We may have already rendered compressed content when using
-  // -compress-debug-sections option. Write it together with header.
-  if (!CompressedData.empty()) {
-    memcpy(Buf, ZDebugHeader.data(), ZDebugHeader.size());
-    memcpy(Buf + ZDebugHeader.size(), CompressedData.data(),
-           CompressedData.size());
-    return;
-  }
-
-  // Write leading padding.
-  uint32_t Filler = getFiller();
-  if (Filler)
-    fill(Buf, Sections.empty() ? Size : Sections[0]->OutSecOff, Filler);
-
-  parallelForEachN(0, Sections.size(), [=](size_t I) {
-    InputSection *Sec = Sections[I];
-    Sec->writeTo<ELFT>(Buf);
-
-    // Fill gaps between sections.
-    if (Filler) {
-      uint8_t *Start = Buf + Sec->OutSecOff + Sec->getSize();
-      uint8_t *End;
-      if (I + 1 == Sections.size())
-        End = Buf + Size;
-      else
-        End = Buf + Sections[I + 1]->OutSecOff;
-      fill(Start, End - Start, Filler);
-    }
-  });
-
-  // Linker scripts may have BYTE()-family commands with which you
-  // can write arbitrary bytes to the output. Process them if any.
-  Script->writeDataBytes(this, Buf);
-}
-
 static uint64_t getOutFlags(InputSectionBase *S) {
   return S->Flags & ~SHF_GROUP & ~SHF_COMPRESSED;
 }
@@ -484,8 +425,3 @@ template void OutputSection::maybeCompress<ELF32LE>();
 template void OutputSection::maybeCompress<ELF32BE>();
 template void OutputSection::maybeCompress<ELF64LE>();
 template void OutputSection::maybeCompress<ELF64BE>();
-
-template void OutputSection::writeTo<ELF32LE>(uint8_t *Buf);
-template void OutputSection::writeTo<ELF32BE>(uint8_t *Buf);
-template void OutputSection::writeTo<ELF64LE>(uint8_t *Buf);
-template void OutputSection::writeTo<ELF64BE>(uint8_t *Buf);

lld/ELF/OutputSections.h

@@ -82,8 +82,6 @@ public:
   void sort(std::function<int(InputSectionBase *S)> Order);
   void sortInitFini();
   void sortCtorsDtors();
-  uint32_t getFiller();
-  template <class ELFT> void writeTo(uint8_t *Buf);
   template <class ELFT> void finalize();
   template <class ELFT> void maybeCompress();
   void assignOffsets();

lld/ELF/SyntheticSections.cpp

@@ -2175,11 +2175,10 @@ MipsRldMapSection::MipsRldMapSection()
 
 void MipsRldMapSection::writeTo(uint8_t *Buf) {
   // Apply filler from linker script.
-  Optional<uint32_t> Fill = Script->getFiller(this->OutSec);
+  uint64_t Filler = Script->getCmd(this->OutSec)->getFiller();
-  if (!Fill || *Fill == 0)
+  if (Filler == 0)
     return;
 
-  uint64_t Filler = *Fill;
   Filler = (Filler << 32) | Filler;
   memcpy(Buf, &Filler, getSize());
 }

lld/ELF/Writer.cpp

@@ -81,6 +81,7 @@ private:
   void addStartStopSymbols(OutputSection *Sec);
   uint64_t getEntryAddr();
   OutputSection *findSection(StringRef Name);
+  OutputSectionCommand *findSectionInScript(StringRef Name);
 
   std::vector<PhdrEntry> Phdrs;
 
@@ -254,13 +255,21 @@ template <class ELFT> void Writer<ELFT>::run() {
   if (ErrorCount)
     return;
 
-  if (Config->Relocatable) {
-    assignFileOffsets();
-  } else {
   if (!Script->Opt.HasSections) {
+    if (!Config->Relocatable)
       fixSectionAlignments();
     Script->fabricateDefaultCommands();
   }
+
+  // If -compressed-debug-sections is specified, we need to compress
+  // .debug_* sections. Do it right now because it changes the size of
+  // output sections.
+  parallelForEach(OutputSections.begin(), OutputSections.end(),
+                  [](OutputSection *S) { S->maybeCompress<ELFT>(); });
+
+  if (Config->Relocatable) {
+    assignFileOffsets();
+  } else {
     Script->synchronize();
     Script->assignAddresses(Phdrs);
 
@@ -1246,12 +1255,6 @@ template <class ELFT> void Writer<ELFT>::finalizeSections() {
   for (OutputSection *Sec : OutputSections)
     Sec->finalize<ELFT>();
 
-  // If -compressed-debug-sections is specified, we need to compress
-  // .debug_* sections. Do it right now because it changes the size of
-  // output sections.
-  parallelForEach(OutputSections.begin(), OutputSections.end(),
-                  [](OutputSection *S) { S->maybeCompress<ELFT>(); });
-
   // createThunks may have added local symbols to the static symbol table
   applySynthetic({InX::SymTab, InX::ShStrTab, InX::StrTab},
                  [](SyntheticSection *SS) { SS->postThunkContents(); });
@@ -1304,6 +1307,15 @@ void Writer<ELFT>::addStartStopSymbols(OutputSection *Sec) {
   addOptionalRegular<ELFT>(Saver.save("__stop_" + S), Sec, -1, STV_DEFAULT);
 }
 
+template <class ELFT>
+OutputSectionCommand *Writer<ELFT>::findSectionInScript(StringRef Name) {
+  for (BaseCommand *Base : Script->Opt.Commands)
+    if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base))
+      if (Cmd->Name == Name)
+        return Cmd;
+  return nullptr;
+}
+
 template <class ELFT> OutputSection *Writer<ELFT>::findSection(StringRef Name) {
   for (OutputSection *Sec : OutputSections)
     if (Sec->Name == Name)
@@ -1743,9 +1755,14 @@ template <class ELFT> void Writer<ELFT>::openFile() {
 
 template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
   uint8_t *Buf = Buffer->getBufferStart();
-  for (OutputSection *Sec : OutputSections)
+  for (BaseCommand *Base : Script->Opt.Commands) {
+    auto *Cmd = dyn_cast<OutputSectionCommand>(Base);
+    if (!Cmd)
+      continue;
+    OutputSection *Sec = Cmd->Sec;
     if (Sec->Flags & SHF_ALLOC)
-      Sec->writeTo<ELFT>(Buf + Sec->Offset);
+      Cmd->writeTo<ELFT>(Buf + Sec->Offset);
+  }
 }
 
 // Write section contents to a mmap'ed file.
@@ -1754,10 +1771,10 @@ template <class ELFT> void Writer<ELFT>::writeSections() {
 
   // PPC64 needs to process relocations in the .opd section
   // before processing relocations in code-containing sections.
-  Out::Opd = findSection(".opd");
+  if (auto *OpdCmd = findSectionInScript(".opd")) {
-  if (Out::Opd) {
+    Out::Opd = OpdCmd->Sec;
     Out::OpdBuf = Buf + Out::Opd->Offset;
-    Out::Opd->template writeTo<ELFT>(Buf + Out::Opd->Offset);
+    OpdCmd->template writeTo<ELFT>(Buf + Out::Opd->Offset);
   }
 
   OutputSection *EhFrameHdr =
@@ -1766,19 +1783,31 @@ template <class ELFT> void Writer<ELFT>::writeSections() {
   // In -r or -emit-relocs mode, write the relocation sections first as in
   // ELf_Rel targets we might find out that we need to modify the relocated
   // section while doing it.
-  for (OutputSection *Sec : OutputSections)
+  for (BaseCommand *Base : Script->Opt.Commands) {
+    auto *Cmd = dyn_cast<OutputSectionCommand>(Base);
+    if (!Cmd)
+      continue;
+    OutputSection *Sec = Cmd->Sec;
     if (Sec->Type == SHT_REL || Sec->Type == SHT_RELA)
-      Sec->writeTo<ELFT>(Buf + Sec->Offset);
+      Cmd->writeTo<ELFT>(Buf + Sec->Offset);
+  }
 
-  for (OutputSection *Sec : OutputSections)
+  for (BaseCommand *Base : Script->Opt.Commands) {
+    auto *Cmd = dyn_cast<OutputSectionCommand>(Base);
+    if (!Cmd)
+      continue;
+    OutputSection *Sec = Cmd->Sec;
     if (Sec != Out::Opd && Sec != EhFrameHdr && Sec->Type != SHT_REL &&
         Sec->Type != SHT_RELA)
-      Sec->writeTo<ELFT>(Buf + Sec->Offset);
+      Cmd->writeTo<ELFT>(Buf + Sec->Offset);
+  }
 
   // The .eh_frame_hdr depends on .eh_frame section contents, therefore
   // it should be written after .eh_frame is written.
-  if (EhFrameHdr && !EhFrameHdr->Sections.empty())
+  if (EhFrameHdr && !EhFrameHdr->Sections.empty()) {
-    EhFrameHdr->writeTo<ELFT>(Buf + EhFrameHdr->Offset);
+    OutputSectionCommand *Cmd = Script->getCmd(EhFrameHdr);
+    Cmd->writeTo<ELFT>(Buf + EhFrameHdr->Offset);
+  }
 }
 
 template <class ELFT> void Writer<ELFT>::writeBuildId() {