[Object] Add the method for checking if a section is a debug section

[jhenderson]

llvm/lib/Object/COFFObjectFile.cpp

332

Is this definitely correct for COFF?

llvm/lib/Object/ObjectFile.cpp

95

This looks to me like an infinite loop?

Maybe this function should just return false?

[djtodoro]

llvm/lib/Object/COFFObjectFile.cpp

332

As far as I can see in the llvm-objcopy tool and on some web pages, but I have not found an official document for that.

llvm/lib/Object/ObjectFile.cpp

95

Hmm.. the false is better option anyway.

[djtodoro]

-addressing a comment

[aprantl]

llvm/lib/Object/COFFObjectFile.cpp

332

You might want to cross-reference this with MCObjectFileInfo.cpp which seems to hardcode these values, too. It looks like this is what is used for DWARF on COFF

[djtodoro]

-addressing a comment

[aprantl]

You could add a unit test for this, but it would effectively be a reimplementation of the function. I'm fine either way.

[jhenderson]

LGTM, but I'd like to see at least one other change that makes use of this to be ready before you commit this, as otherwise this is just dead and untested code. I agree a unit test probably doesn't make much sense.

[djtodoro]

Can this go as is, since the D74205 has a few tests using this? I agree a unit test is not the best solution for this..

[jhenderson]

In D76276#1954794, @djtodoro wrote:

Can this go as is, since the D74205 has a few tests using this? I agree a unit test is not the best solution for this..

Right, sorry for the confusion. Now that D74205 is ready to land, this is good to go.

llvm/include/llvm/Object/COFF.h

protected:
   Expected<ArrayRef<uint8_t>>
   getSectionContents(DataRefImpl Sec) const override;
   uint64_t getSectionAlignment(DataRefImpl Sec) const override;
   bool isSectionCompressed(DataRefImpl Sec) const override;
   bool isSectionText(DataRefImpl Sec) const override;
   bool isSectionData(DataRefImpl Sec) const override;
   bool isSectionBSS(DataRefImpl Sec) const override;
   bool isSectionVirtual(DataRefImpl Sec) const override;
+  bool isDebugSection(StringRef SectionName) const override;
   relocation_iterator section_rel_begin(DataRefImpl Sec) const override;
   relocation_iterator section_rel_end(DataRefImpl Sec) const override;
 
   void moveRelocationNext(DataRefImpl &Rel) const override;
   uint64_t getRelocationOffset(DataRefImpl Rel) const override;
   symbol_iterator getRelocationSymbol(DataRefImpl Rel) const override;
   uint64_t getRelocationType(DataRefImpl Rel) const override;
   void getRelocationTypeName(DataRefImpl Rel,

llvm/include/llvm/Object/ELFObjectFile.h

protected:
   uint64_t getSectionAlignment(DataRefImpl Sec) const override;
   bool isSectionCompressed(DataRefImpl Sec) const override;
   bool isSectionText(DataRefImpl Sec) const override;
   bool isSectionData(DataRefImpl Sec) const override;
   bool isSectionBSS(DataRefImpl Sec) const override;
   bool isSectionVirtual(DataRefImpl Sec) const override;
   bool isBerkeleyText(DataRefImpl Sec) const override;
   bool isBerkeleyData(DataRefImpl Sec) const override;
+  bool isDebugSection(StringRef SectionName) const override;
   relocation_iterator section_rel_begin(DataRefImpl Sec) const override;
   relocation_iterator section_rel_end(DataRefImpl Sec) const override;
   std::vector<SectionRef> dynamic_relocation_sections() const override;
   Expected<section_iterator>
   getRelocatedSection(DataRefImpl Sec) const override;
 
   void moveRelocationNext(DataRefImpl &Rel) const override;
   uint64_t getRelocationOffset(DataRefImpl Rel) const override;

 template <class ELFT>
 bool ELFObjectFile<ELFT>::isBerkeleyData(DataRefImpl Sec) const {
   const Elf_Shdr *EShdr = getSection(Sec);
   return !isBerkeleyText(Sec) && EShdr->sh_type != ELF::SHT_NOBITS &&
          EShdr->sh_flags & ELF::SHF_ALLOC;
 }
 
 template <class ELFT>
+bool ELFObjectFile<ELFT>::isDebugSection(StringRef SectionName) const {
+  return SectionName.startswith(".debug") ||
+         SectionName.startswith(".zdebug") || SectionName == ".gdb_index";
+}
+
+template <class ELFT>
 relocation_iterator
 ELFObjectFile<ELFT>::section_rel_begin(DataRefImpl Sec) const {
   DataRefImpl RelData;
   auto SectionsOrErr = EF.sections();
   if (!SectionsOrErr)
     return relocation_iterator(RelocationRef());
   uintptr_t SHT = reinterpret_cast<uintptr_t>((*SectionsOrErr).begin());
   RelData.d.a = (Sec.p - SHT) / EF.getHeader()->e_shentsize;

llvm/include/llvm/Object/MachO.h

public:
   Expected<SectionRef> getSection(unsigned SectionIndex) const;
   Expected<SectionRef> getSection(StringRef SectionName) const;
   bool isSectionCompressed(DataRefImpl Sec) const override;
   bool isSectionText(DataRefImpl Sec) const override;
   bool isSectionData(DataRefImpl Sec) const override;
   bool isSectionBSS(DataRefImpl Sec) const override;
   bool isSectionVirtual(DataRefImpl Sec) const override;
   bool isSectionBitcode(DataRefImpl Sec) const override;
+  bool isDebugSection(StringRef SectionName) const override;
 
   /// When dsymutil generates the companion file, it strips all unnecessary
   /// sections (e.g. everything in the _TEXT segment) by omitting their body
   /// and setting the offset in their corresponding load command to zero.
   ///
   /// While the load command itself is valid, reading the section corresponds
   /// to reading the number of bytes specified in the load command, starting
   /// from offset 0 (i.e. the Mach-O header at the beginning of the file).

llvm/include/llvm/Object/ObjectFile.h

public:
   /// Berkeley size format. This is true if the section is allocatable, and
   /// contains either code or readonly data.
   bool isBerkeleyText() const;
   /// Whether this section will be placed in the data segment, according to the
   /// Berkeley size format. This is true if the section is allocatable and
   /// contains data (e.g. PROGBITS), but is not text.
   bool isBerkeleyData() const;
 
+  /// Whether this section is a debug section.
+  bool isDebugSection(StringRef SectionName) const;
+
   bool containsSymbol(SymbolRef S) const;
 
   relocation_iterator relocation_begin() const;
   relocation_iterator relocation_end() const;
   iterator_range<relocation_iterator> relocations() const {
     return make_range(relocation_begin(), relocation_end());
   }
   Expected<section_iterator> getRelocatedSection() const;
protected:
   virtual bool isSectionData(DataRefImpl Sec) const = 0;
   virtual bool isSectionBSS(DataRefImpl Sec) const = 0;
   // A section is 'virtual' if its contents aren't present in the object image.
   virtual bool isSectionVirtual(DataRefImpl Sec) const = 0;
   virtual bool isSectionBitcode(DataRefImpl Sec) const;
   virtual bool isSectionStripped(DataRefImpl Sec) const;
   virtual bool isBerkeleyText(DataRefImpl Sec) const;
   virtual bool isBerkeleyData(DataRefImpl Sec) const;
+  virtual bool isDebugSection(StringRef SectionName) const;
   virtual relocation_iterator section_rel_begin(DataRefImpl Sec) const = 0;
   virtual relocation_iterator section_rel_end(DataRefImpl Sec) const = 0;
   virtual Expected<section_iterator> getRelocatedSection(DataRefImpl Sec) const;
 
   // Same as above for RelocationRef.
   friend class RelocationRef;
   virtual void moveRelocationNext(DataRefImpl &Rel) const = 0;
   virtual uint64_t getRelocationOffset(DataRefImpl Rel) const = 0;

 inline bool SectionRef::isBerkeleyText() const {
   return OwningObject->isBerkeleyText(SectionPimpl);
 }
 
 inline bool SectionRef::isBerkeleyData() const {
   return OwningObject->isBerkeleyData(SectionPimpl);
 }
 
+inline bool SectionRef::isDebugSection(StringRef SectionName) const {
+  return OwningObject->isDebugSection(SectionName);
+}
+
 inline relocation_iterator SectionRef::relocation_begin() const {
   return OwningObject->section_rel_begin(SectionPimpl);
 }
 
 inline relocation_iterator SectionRef::relocation_end() const {
   return OwningObject->section_rel_end(SectionPimpl);
 }
 

llvm/lib/Object/COFFObjectFile.cpp

 bool COFFObjectFile::isSectionBSS(DataRefImpl Ref) const {
   const coff_section *Sec = toSec(Ref);
   const uint32_t BssFlags = COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
                             COFF::IMAGE_SCN_MEM_READ |
                             COFF::IMAGE_SCN_MEM_WRITE;
   return (Sec->Characteristics & BssFlags) == BssFlags;
 }
 
+// The .debug sections are the only debug sections for COFF
+// (\see MCObjectFileInfo.cpp).
+bool COFFObjectFile::isDebugSection(StringRef SectionName) const {
+  return SectionName.startswith(".debug");
+}
+
 unsigned COFFObjectFile::getSectionID(SectionRef Sec) const {
   uintptr_t Offset =
       uintptr_t(Sec.getRawDataRefImpl().p) - uintptr_t(SectionTable);
   assert((Offset % sizeof(coff_section)) == 0);
   return (Offset / sizeof(coff_section)) + 1;
 }
 
 bool COFFObjectFile::isSectionVirtual(DataRefImpl Ref) const {

llvm/lib/Object/MachOObjectFile.cpp

 bool MachOObjectFile::isSectionBSS(DataRefImpl Sec) const {
   uint32_t Flags = getSectionFlags(*this, Sec);
   unsigned SectionType = Flags & MachO::SECTION_TYPE;
   return !(Flags & MachO::S_ATTR_PURE_INSTRUCTIONS) &&
          (SectionType == MachO::S_ZEROFILL ||
           SectionType == MachO::S_GB_ZEROFILL);
 }
 
+bool MachOObjectFile::isDebugSection(StringRef SectionName) const {
+  return SectionName.startswith("__debug") ||
+         SectionName.startswith("__zdebug") || SectionName == "__gdb_index";
+}
+
 unsigned MachOObjectFile::getSectionID(SectionRef Sec) const {
   return Sec.getRawDataRefImpl().d.a;
 }
 
 bool MachOObjectFile::isSectionVirtual(DataRefImpl Sec) const {
   uint32_t Flags = getSectionFlags(*this, Sec);
   unsigned SectionType = Flags & MachO::SECTION_TYPE;
   return SectionType == MachO::S_ZEROFILL ||

llvm/lib/Object/ObjectFile.cpp

 bool ObjectFile::isBerkeleyText(DataRefImpl Sec) const {
   return isSectionText(Sec);
 }
 
 bool ObjectFile::isBerkeleyData(DataRefImpl Sec) const {
   return isSectionData(Sec);
 }
 
+bool ObjectFile::isDebugSection(StringRef SectionName) const {
+  return false;
+}
+
 Expected<section_iterator>
 ObjectFile::getRelocatedSection(DataRefImpl Sec) const {
   return section_iterator(SectionRef(Sec, this));
 }
 
 Triple ObjectFile::makeTriple() const {
   Triple TheTriple;
   auto Arch = getArch();