[DWARFYAML] Make the debug_aranges entry optional.

[Higuoxing]

Summary

This patch makes the 'debug_aranges' entry optional. If the entry is
empty, yaml2obj will only emit the header for it.

[jhenderson]

llvm/tools/obj2yaml/dwarf2yaml.cpp

67

It seems to me like you don't need this vector? Could you do Y.DebugAranges.emplace() to instantiate the vector in this case?

[Higuoxing]

llvm/tools/obj2yaml/dwarf2yaml.cpp

67

Actually I do it deliberately here. IMHO, if the parser encounters an error below, debug_aranges entry should keep empty.

In the implementation of adding DWARF support to elf2yaml, the basic idea is that firstly, we try to parse DWARF sections into the "DWARF:" entry, if the parser fails, elf2yaml will consume that error and continue to dump it as raw content. If we don't do it here, the "DWARF:" will have an incomplete section.

Shall we wait for the patch that adds DWARF support to elf2yaml to see if it works?

[Higuoxing]

Seems that some bots are not happy with this patch, I'll look into it.

[jhenderson]

llvm/tools/obj2yaml/dwarf2yaml.cpp

67

Thanks for the explanation. What you say makes sense to me.

[Higuoxing]

Add dependency to suppress errors.

[Higuoxing]

Update.

[jhenderson]

LGTM.

llvm/include/llvm/ObjectYAML/DWARFYAML.h

 };
 
 struct Data {
   bool IsLittleEndian;
   bool Is64BitAddrSize;
   std::vector<Abbrev> AbbrevDecls;
   std::vector<StringRef> DebugStrings;
   Optional<std::vector<StringOffsetsTable>> DebugStrOffsets;
-  std::vector<ARange> ARanges;
+  Optional<std::vector<ARange>> DebugAranges;
   std::vector<Ranges> DebugRanges;
   std::vector<AddrTableEntry> DebugAddr;
   Optional<PubSection> PubNames;
   Optional<PubSection> PubTypes;
 
   Optional<PubSection> GNUPubNames;
   Optional<PubSection> GNUPubTypes;
 

llvm/lib/ObjectYAML/DWARFEmitter.cpp

Error DWARFYAML::emitDebugAbbrev(raw_ostream &OS, const DWARFYAML::Data &DI) {
   // The abbreviations for a given compilation unit end with an entry consisting
   // of a 0 byte for the abbreviation code.
   OS.write_zeros(1);
 
   return Error::success();
 }
 
 Error DWARFYAML::emitDebugAranges(raw_ostream &OS, const DWARFYAML::Data &DI) {
-  for (auto Range : DI.ARanges) {
+  assert(DI.DebugAranges && "unexpected emitDebugAranges() call");
+  for (auto Range : *DI.DebugAranges) {
     uint8_t AddrSize;
     if (Range.AddrSize)
       AddrSize = *Range.AddrSize;
     else
       AddrSize = DI.Is64BitAddrSize ? 8 : 4;
 
     uint64_t Length = 4; // sizeof(version) 2 + sizeof(address_size) 1 +
                          // sizeof(segment_selector_size) 1

llvm/lib/ObjectYAML/DWARFYAML.cpp

 //===----------------------------------------------------------------------===//
 
 #include "llvm/ObjectYAML/DWARFYAML.h"
 #include "llvm/BinaryFormat/Dwarf.h"
 
 namespace llvm {
 
 bool DWARFYAML::Data::isEmpty() const {
-  return DebugStrings.empty() && AbbrevDecls.empty() && ARanges.empty() &&
+  return DebugStrings.empty() && AbbrevDecls.empty() && DebugAranges &&
          DebugRanges.empty() && !PubNames && !PubTypes && !GNUPubNames &&
          !GNUPubTypes && CompileUnits.empty() && DebugLines.empty();
 }
 
 SetVector<StringRef> DWARFYAML::Data::getNonEmptySectionNames() const {
   SetVector<StringRef> SecNames;
   if (!DebugStrings.empty())
     SecNames.insert("debug_str");
-  if (!ARanges.empty())
+  if (DebugAranges)
     SecNames.insert("debug_aranges");
   if (!DebugRanges.empty())
     SecNames.insert("debug_ranges");
   if (!DebugLines.empty())
     SecNames.insert("debug_line");
   if (!DebugAddr.empty())
     SecNames.insert("debug_addr");
   if (!AbbrevDecls.empty())

 namespace yaml {
 
 void MappingTraits<DWARFYAML::Data>::mapping(IO &IO, DWARFYAML::Data &DWARF) {
   void *OldContext = IO.getContext();
   DWARFYAML::DWARFContext DWARFCtx;
   IO.setContext(&DWARFCtx);
   IO.mapOptional("debug_str", DWARF.DebugStrings);
   IO.mapOptional("debug_abbrev", DWARF.AbbrevDecls);
-  if (!DWARF.ARanges.empty() || !IO.outputting())
-    IO.mapOptional("debug_aranges", DWARF.ARanges);
+  IO.mapOptional("debug_aranges", DWARF.DebugAranges);
   if (!DWARF.DebugRanges.empty() || !IO.outputting())
     IO.mapOptional("debug_ranges", DWARF.DebugRanges);
   IO.mapOptional("debug_pubnames", DWARF.PubNames);
   IO.mapOptional("debug_pubtypes", DWARF.PubTypes);
   DWARFCtx.IsGNUPubSec = true;
   IO.mapOptional("debug_gnu_pubnames", DWARF.GNUPubNames);
   IO.mapOptional("debug_gnu_pubtypes", DWARF.GNUPubTypes);
   IO.mapOptional("debug_info", DWARF.CompileUnits);

llvm/lib/ObjectYAML/MachOEmitter.cpp

case MachO::LC_SEGMENT_64:
         if (0 == strncmp(&Sec.segname[0], "__DWARF", 16)) {
           Error Err = Error::success();
           cantFail(std::move(Err));
 
           if (0 == strncmp(&Sec.sectname[0], "__debug_str", 16))
             Err = DWARFYAML::emitDebugStr(OS, Obj.DWARF);
           else if (0 == strncmp(&Sec.sectname[0], "__debug_abbrev", 16))
             Err = DWARFYAML::emitDebugAbbrev(OS, Obj.DWARF);
-          else if (0 == strncmp(&Sec.sectname[0], "__debug_aranges", 16))
+          else if (0 == strncmp(&Sec.sectname[0], "__debug_aranges", 16)) {
+            if (Obj.DWARF.DebugAranges)
               Err = DWARFYAML::emitDebugAranges(OS, Obj.DWARF);
-          else if (0 == strncmp(&Sec.sectname[0], "__debug_ranges", 16))
+          } else if (0 == strncmp(&Sec.sectname[0], "__debug_ranges", 16))
             Err = DWARFYAML::emitDebugRanges(OS, Obj.DWARF);
           else if (0 == strncmp(&Sec.sectname[0], "__debug_pubnames", 16)) {
             if (Obj.DWARF.PubNames)
               Err = DWARFYAML::emitDebugPubnames(OS, Obj.DWARF);
           } else if (0 == strncmp(&Sec.sectname[0], "__debug_pubtypes", 16)) {
             if (Obj.DWARF.PubTypes)
               Err = DWARFYAML::emitDebugPubtypes(OS, Obj.DWARF);
           } else if (0 == strncmp(&Sec.sectname[0], "__debug_info", 16))

llvm/test/ObjectYAML/MachO/DWARF-debug_aranges.yaml

-# RUN: yaml2obj %s | obj2yaml | FileCheck %s
+## a) Test that yaml2macho is able to emit the .debug_aranges section and obj2yaml
+## is able to convert it back.
+
+# RUN: yaml2obj --docnum=1 %s | obj2yaml | FileCheck %s
 
 --- !mach-o
 FileHeader:      
   magic:           0xFEEDFACF
   cputype:         0x01000007
   cpusubtype:      0x00000003
   filetype:        0x0000000A
   ncmds:           7

 #      CHECK:   debug_aranges:
 # CHECK-NEXT:     - Length:              0x000000000000002C
 # CHECK-NEXT:       Version:             2
 # CHECK-NEXT:       CuOffset:            0x0000000000000000
 # CHECK-NEXT:       AddressSize:         0x08
 # CHECK-NEXT:       Descriptors:
 # CHECK-NEXT:         - Address: 0x0000000100000F50
 # CHECK-NEXT:           Length:  52
+
+## b) Test that if the "debug_aranges" entry is empty, yaml2macho will only emit the
+## section header.
+
+# RUN: yaml2obj --docnum=2 %s -o %t2.o
+# RUN: llvm-readobj --sections --section-data %t2.o | FileCheck %s --check-prefix=EMPTY-SECTION
+
+#      EMPTY-SECTION: Index: 0
+# EMPTY-SECTION-NEXT: Name: __debug_aranges (5F 5F 64 65 62 75 67 5F 61 72 61 6E 67 65 73 00)
+# EMPTY-SECTION-NEXT: Segment: __DWARF (5F 5F 44 57 41 52 46 00 00 00 00 00 00 00 00 00)
+# EMPTY-SECTION-NEXT: Address: 0x0
+# EMPTY-SECTION-NEXT: Size: 0xC
+# EMPTY-SECTION-NEXT: Offset: 528
+# EMPTY-SECTION-NEXT: Alignment: 0
+# EMPTY-SECTION-NEXT: RelocationOffset: 0x0
+# EMPTY-SECTION-NEXT: RelocationCount: 0
+# EMPTY-SECTION-NEXT: Type: Regular (0x0)
+# EMPTY-SECTION-NEXT: Attributes [ (0x0)
+# EMPTY-SECTION-NEXT: ]
+# EMPTY-SECTION-NEXT: Reserved1: 0x0
+# EMPTY-SECTION-NEXT: Reserved2: 0x0
+# EMPTY-SECTION-NEXT: Reserved3: 0x0
+# EMPTY-SECTION-NEXT: SectionData (
+# EMPTY-SECTION-NEXT: )
+
+--- !mach-o
+FileHeader:
+  magic:      0xFEEDFACF
+  cputype:    0x01000007
+  cpusubtype: 0x00000003
+  filetype:   0x0000000A
+  ncmds:      1
+  sizeofcmds: 232
+  flags:      0x00000000
+  reserved:   0x00000000
+LoadCommands:
+  - cmd:      LC_SEGMENT_64
+    cmdsize:  152
+    segname:  __DWARF
+    vmaddr:   0x00
+    vmsize:   0x00
+    fileoff:  0x00
+    filesize: 0x00
+    maxprot:  0
+    initprot: 0
+    nsects:   1
+    flags:    0
+    Sections:
+      - sectname:  __debug_aranges
+        segname:   __DWARF
+        addr:      0x00
+        size:      12
+        offset:    528
+        align:     0
+        reloff:    0x00000000
+        nreloc:    0
+        flags:     0x00000000
+        reserved1: 0x00000000
+        reserved2: 0x00000000
+        reserved3: 0x00000000
+DWARF:
+  debug_aranges: []

llvm/test/tools/yaml2obj/ELF/DWARF/debug-aranges.yaml

- Version:  2
           Length:  0x1000
     - Format:      DWARF64
       Version:     2
       AddressSize: [[ADDRSIZE]]
       CuOffset:    0
       Descriptors:
         - Address: 0x1234
           Length:  0x4321
+
+## l) Test that the .debug_aranges section header is emitted if the "debug_aranges"
+## entry is empty.
+
+# RUN: yaml2obj --docnum=12 %s -o %t12.o
+# RUN: llvm-readobj --sections --section-data %t12.o | \
+# RUN:   FileCheck -DSIZE=0 -DADDRALIGN=1 %s --check-prefixes=DWARF-HEADER,EMPTY-CONTENT
+
+# EMPTY-CONTENT-NEXT: SectionData (
+# EMPTY-CONTENT-NEXT: )
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+DWARF:
+  debug_aranges: []

llvm/tools/obj2yaml/dwarf2yaml.cpp

void dumpDebugStrings(DWARFContext &DCtx, DWARFYAML::Data &Y) {
   }
 }
 
 Error dumpDebugARanges(DWARFContext &DCtx, DWARFYAML::Data &Y) {
   DWARFDataExtractor ArangesData(DCtx.getDWARFObj().getArangesSection(),
                                  DCtx.isLittleEndian(), 0);
   uint64_t Offset = 0;
   DWARFDebugArangeSet Set;
-
+  std::vector<DWARFYAML::ARange> DebugAranges;
   while (ArangesData.isValidOffset(Offset)) {
     if (Error E = Set.extract(ArangesData, &Offset))
       return E;
     DWARFYAML::ARange Range;
     Range.Format = Set.getHeader().Format;
     Range.Length = Set.getHeader().Length;
     Range.Version = Set.getHeader().Version;
     Range.CuOffset = Set.getHeader().CuOffset;
     Range.AddrSize = Set.getHeader().AddrSize;
     Range.SegSize = Set.getHeader().SegSize;
     for (auto Descriptor : Set.descriptors()) {
       DWARFYAML::ARangeDescriptor Desc;
       Desc.Address = Descriptor.Address;
       Desc.Length = Descriptor.Length;
       Range.Descriptors.push_back(Desc);
     }
-    Y.ARanges.push_back(Range);
+    DebugAranges.push_back(Range);
   }
+
+  Y.DebugAranges = DebugAranges;
   return ErrorSuccess();
 }
 
 Error dumpDebugRanges(DWARFContext &DCtx, DWARFYAML::Data &Y) {
   // We are assuming all address byte sizes will be consistent across all
   // compile units.
   uint8_t AddrSize = 0;
   for (const auto &CU : DCtx.compile_units()) {