[ELF] Make .comment have a non-full file

This ensures that SectionBase::file is non-null except
InputSection::discarded.

Author: MaskRay

lld/ELF/Driver.cpp

@@ -3147,7 +3147,7 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
 
   // This adds a .comment section containing a version string.
   if (!ctx.arg.relocatable)
-    ctx.inputSections.push_back(createCommentSection());
+    ctx.inputSections.push_back(createCommentSection(ctx));
 
   // Split SHF_MERGE and .eh_frame sections into pieces in preparation for garbage collection.
   splitSections<ELFT>(ctx);

lld/ELF/InputSection.cpp

@@ -299,10 +299,6 @@ std::string InputSectionBase::getLocation(uint64_t offset) const {
   std::string secAndOffset =
       (name + "+0x" + Twine::utohexstr(offset) + ")").str();
 
-  // We don't have file for synthetic sections.
-  if (file == nullptr)
-    return (ctx.arg.outputFile + ":(" + secAndOffset).str();
-
   std::string filename = toString(file);
   if (Defined *d = getEnclosingFunction(offset))
     return filename + ":(function " + toString(*d) + ": " + secAndOffset;
@@ -1430,11 +1426,12 @@ MergeInputSection::MergeInputSection(ObjFile<ELFT> &f,
                                      StringRef name)
     : InputSectionBase(f, header, name, InputSectionBase::Merge) {}
 
-MergeInputSection::MergeInputSection(uint64_t flags, uint32_t type,
+MergeInputSection::MergeInputSection(Ctx &ctx, uint64_t flags, uint32_t type,
                                      uint64_t entsize, ArrayRef<uint8_t> data,
                                      StringRef name)
-    : InputSectionBase(nullptr, flags, type, entsize, /*Link*/ 0, /*Info*/ 0,
-                       /*Alignment*/ entsize, data, name, SectionBase::Merge) {}
+    : InputSectionBase(ctx.internalFile, flags, type, entsize, /*link=*/0,
+                       /*info=*/0,
+                       /*alignment=*/entsize, data, name, SectionBase::Merge) {}
 
 // This function is called after we obtain a complete list of input sections
 // that need to be linked. This is responsible to split section contents

lld/ELF/InputSection.h

@@ -316,7 +316,7 @@ class MergeInputSection : public InputSectionBase {
   template <class ELFT>
   MergeInputSection(ObjFile<ELFT> &f, const typename ELFT::Shdr &header,
                     StringRef name);
-  MergeInputSection(uint64_t flags, uint32_t type, uint64_t entsize,
+  MergeInputSection(Ctx &, uint64_t flags, uint32_t type, uint64_t entsize,
                     ArrayRef<uint8_t> data, StringRef name);
 
   static bool classof(const SectionBase *s) { return s->kind() == Merge; }

lld/ELF/SyntheticSections.cpp

@@ -87,9 +87,9 @@ static ArrayRef<uint8_t> getVersion() {
 // With this feature, you can identify LLD-generated binaries easily
 // by "readelf --string-dump .comment <file>".
 // The returned object is a mergeable string section.
-MergeInputSection *elf::createCommentSection() {
-  auto *sec = make<MergeInputSection>(SHF_MERGE | SHF_STRINGS, SHT_PROGBITS, 1,
-                                      getVersion(), ".comment");
+MergeInputSection *elf::createCommentSection(Ctx &ctx) {
+  auto *sec = make<MergeInputSection>(
+      ctx, SHF_MERGE | SHF_STRINGS, SHT_PROGBITS, 1, getVersion(), ".comment");
   sec->splitIntoPieces();
   return sec;
 }

lld/ELF/SyntheticSections.h

@@ -1429,7 +1429,7 @@ class MemtagGlobalDescriptors final : public SyntheticSection {
 
 template <class ELFT> void createSyntheticSections(Ctx &);
 InputSection *createInterpSection(Ctx &);
-MergeInputSection *createCommentSection();
+MergeInputSection *createCommentSection(Ctx &);
 template <class ELFT> void splitSections(Ctx &);
 void combineEhSections(Ctx &);