[DWARFYAML] Make the debug_ranges section optional.

This patch makes the debug_ranges section optional. When we specify an
empty debug_ranges section, yaml2obj only emits the section header.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D87263

6 files changed, 67 insertions, 6 deletions

diff --git a/llvm/include/llvm/ObjectYAML/DWARFYAML.h b/llvm/include/llvm/ObjectYAML/DWARFYAML.h
index 99a7af8..3e5be41 100644
--- a/llvm/include/llvm/ObjectYAML/DWARFYAML.h
+++ b/llvm/include/llvm/ObjectYAML/DWARFYAML.h
@@ -214,7 +214,7 @@ struct Data {
   Optional<std::vector<StringRef>> DebugStrings;
   Optional<std::vector<StringOffsetsTable>> DebugStrOffsets;
   Optional<std::vector<ARange>> DebugAranges;
-  std::vector<Ranges> DebugRanges;
+  Optional<std::vector<Ranges>> DebugRanges;
   Optional<std::vector<AddrTableEntry>> DebugAddr;
   Optional<PubSection> PubNames;
   Optional<PubSection> PubTypes;
diff --git a/llvm/lib/ObjectYAML/DWARFEmitter.cpp b/llvm/lib/ObjectYAML/DWARFEmitter.cpp
index bf29f40..b634f7c 100644
--- a/llvm/lib/ObjectYAML/DWARFEmitter.cpp
+++ b/llvm/lib/ObjectYAML/DWARFEmitter.cpp
@@ -190,7 +190,7 @@ Error DWARFYAML::emitDebugAranges(raw_ostream &OS, const DWARFYAML::Data &DI) {
 Error DWARFYAML::emitDebugRanges(raw_ostream &OS, const DWARFYAML::Data &DI) {
   const size_t RangesOffset = OS.tell();
   uint64_t EntryIndex = 0;
-  for (auto DebugRanges : DI.DebugRanges) {
+  for (auto DebugRanges : *DI.DebugRanges) {
     const size_t CurrOffset = OS.tell() - RangesOffset;
     if (DebugRanges.Offset && (uint64_t)*DebugRanges.Offset < CurrOffset)
       return createStringError(errc::invalid_argument,
diff --git a/llvm/lib/ObjectYAML/DWARFYAML.cpp b/llvm/lib/ObjectYAML/DWARFYAML.cpp
index 353e505..975b9b4 100644
--- a/llvm/lib/ObjectYAML/DWARFYAML.cpp
+++ b/llvm/lib/ObjectYAML/DWARFYAML.cpp
@@ -28,7 +28,7 @@ SetVector<StringRef> DWARFYAML::Data::getNonEmptySectionNames() const {
     SecNames.insert("debug_str");
   if (DebugAranges)
     SecNames.insert("debug_aranges");
-  if (!DebugRanges.empty())
+  if (DebugRanges)
     SecNames.insert("debug_ranges");
   if (!DebugLines.empty())
     SecNames.insert("debug_line");
@@ -95,8 +95,7 @@ void MappingTraits<DWARFYAML::Data>::mapping(IO &IO, DWARFYAML::Data &DWARF) {
   IO.mapOptional("debug_str", DWARF.DebugStrings);
   IO.mapOptional("debug_abbrev", DWARF.DebugAbbrev);
   IO.mapOptional("debug_aranges", DWARF.DebugAranges);
-  if (!DWARF.DebugRanges.empty() || !IO.outputting())
-    IO.mapOptional("debug_ranges", DWARF.DebugRanges);
+  IO.mapOptional("debug_ranges", DWARF.DebugRanges);
   IO.mapOptional("debug_pubnames", DWARF.PubNames);
   IO.mapOptional("debug_pubtypes", DWARF.PubTypes);
   DWARFCtx.IsGNUPubSec = true;
diff --git a/llvm/test/ObjectYAML/MachO/DWARF-debug_ranges.yaml b/llvm/test/ObjectYAML/MachO/DWARF-debug_ranges.yaml
index 8948bf9..30997ba 100644
--- a/llvm/test/ObjectYAML/MachO/DWARF-debug_ranges.yaml
+++ b/llvm/test/ObjectYAML/MachO/DWARF-debug_ranges.yaml
@@ -239,3 +239,48 @@ DWARF:
         - AbbrCode:        0x00000000
           Values:          []
 ...
+
+## Test generating and dumping an empty __debug_ranges section.
+
+# RUN: yaml2obj --docnum=2 %s | obj2yaml | FileCheck %s --check-prefix=EMPTY
+
+#      EMPTY: DWARF:
+# EMPTY-NEXT:   debug_ranges:    []
+# EMPTY-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_ranges
+        segname:   __DWARF
+        addr:      0x00
+        size:      [[SIZE=0]]
+        offset:    0x210
+        align:     0
+        reloff:    0x00000000
+        nreloc:    0
+        flags:     0x00000000
+        reserved1: 0x00000000
+        reserved2: 0x00000000
+        reserved3: 0x00000000
+        content:   [[CONTENT=<none>]]
diff --git a/llvm/test/tools/yaml2obj/ELF/DWARF/debug-ranges.yaml b/llvm/test/tools/yaml2obj/ELF/DWARF/debug-ranges.yaml
index 6a9cd7a6..f80dd6d 100644
--- a/llvm/test/tools/yaml2obj/ELF/DWARF/debug-ranges.yaml
+++ b/llvm/test/tools/yaml2obj/ELF/DWARF/debug-ranges.yaml
@@ -407,3 +407,17 @@ DWARF:
       Entries:
         - LowOffset:  0x1234
           HighOffset: 0x5678
+
+## l) Test that the .debug_ranges section header is emitted if the "debug_ranges"
+## entry is empty.
+
+# RUN: yaml2obj --docnum=12 %s -o %t12.o
+# RUN: llvm-readobj -S %t12.o | FileCheck -DSIZE=0 -DADDRALIGN=1 %s --check-prefix=DWARF-HEADER
+
+--- !ELF
+FileHeader:
+  Class: ELFCLASS64
+  Data:  ELFDATA2LSB
+  Type:  ET_EXEC
+DWARF:
+  debug_ranges: []
diff --git a/llvm/tools/obj2yaml/dwarf2yaml.cpp b/llvm/tools/obj2yaml/dwarf2yaml.cpp
index cef7b69..1dcf6d4 100644
--- a/llvm/tools/obj2yaml/dwarf2yaml.cpp
+++ b/llvm/tools/obj2yaml/dwarf2yaml.cpp
@@ -114,6 +114,7 @@ Error dumpDebugRanges(DWARFContext &DCtx, DWARFYAML::Data &Y) {
                           DCtx.isLittleEndian(), AddrSize);
   uint64_t Offset = 0;
   DWARFDebugRangeList DwarfRanges;
+  std::vector<DWARFYAML::Ranges> DebugRanges;
 
   while (Data.isValidOffset(Offset)) {
     DWARFYAML::Ranges YamlRanges;
@@ -123,8 +124,10 @@ Error dumpDebugRanges(DWARFContext &DCtx, DWARFYAML::Data &Y) {
       return E;
     for (const auto &RLE : DwarfRanges.getEntries())
       YamlRanges.Entries.push_back({RLE.StartAddress, RLE.EndAddress});
-    Y.DebugRanges.push_back(std::move(YamlRanges));
+    DebugRanges.push_back(std::move(YamlRanges));
   }
+
+  Y.DebugRanges = DebugRanges;
   return ErrorSuccess();
 }