[DWARF] Add API to get data from MCDwarfLineStr

[ayermolo]

Summary

This API will be used in D121876, to get finalized string data for
.debug_line_str.

[ayermolo]

@dblaikie Do you think this is in your wheelhouse to review, or should I find someone else?
thanks

[dblaikie]

Generally we'd rather not commit untested functionality - /probably/ this should be either unit tested in this commit, or rolled into whatever commit calls/exercises the functionality. But if you reckon this is really the better separation, I won't insist on that, but give it some thought.

[ayermolo]

In D124052#3463847, @dblaikie wrote:

Generally we'd rather not commit untested functionality - /probably/ this should be either unit tested in this commit, or rolled into whatever commit calls/exercises the functionality. But if you reckon this is really the better separation, I won't insist on that, but give it some thought.

Thanks. I'll add a unit test. Probably more inline with what I have seen from other diffs of breaking them up if possible. The other commit is already pretty big.

[ayermolo]

modified one of the tests to test new API.

[ayermolo]

removing include that snuck in

[rafauler]

LGTM

llvm/include/llvm/MC/MCDwarf.h

public:
   /// v5 line table).
   explicit MCDwarfLineStr(MCContext &Ctx);
 
   /// Emit a reference to the string.
   void emitRef(MCStreamer *MCOS, StringRef Path);
 
   /// Emit the .debug_line_str section if appropriate.
   void emitSection(MCStreamer *MCOS);
+
+  /// Returns finalized section.
+  SmallString<0> getFinalizedData();
 };
 
 /// Instances of this class represent the name of the dwarf .file directive and
 /// its associated dwarf file number in the MC file. MCDwarfFile's are created
 /// and uniqued by the MCContext class. In Dwarf 4 file numbers start from 1;
 /// i.e. the entry with file number 1 is the first element in the vector of
 /// DwarfFiles and there is no MCDwarfFile with file number 0. In Dwarf 5 file
 /// numbers start from 0, with the MCDwarfFile with file number 0 being the

llvm/include/llvm/MC/StringTableBuilder.h

public:
   }
 
   size_t getSize() const { return Size; }
   void clear();
 
   void write(raw_ostream &OS) const;
   void write(uint8_t *Buf) const;
 
-private:
   bool isFinalized() const { return Finalized; }
 };
 
 } // end namespace llvm
 
 #endif // LLVM_MC_STRINGTABLEBUILDER_H

llvm/lib/MC/MCDwarf.cpp

static void emitAbsValue(MCStreamer &OS, const MCExpr *Value, unsigned Size) {
   const MCExpr *ABS = forceExpAbs(OS, Value);
   OS.emitValue(ABS, Size);
 }
 
 void MCDwarfLineStr::emitSection(MCStreamer *MCOS) {
   // Switch to the .debug_line_str section.
   MCOS->SwitchSection(
       MCOS->getContext().getObjectFileInfo()->getDwarfLineStrSection());
+  SmallString<0> Data = getFinalizedData();
+  MCOS->emitBinaryData(Data.str());
+}
+
+SmallString<0> MCDwarfLineStr::getFinalizedData() {
   // Emit the strings without perturbing the offsets we used.
+  if (!LineStrings.isFinalized())
     LineStrings.finalizeInOrder();
   SmallString<0> Data;
   Data.resize(LineStrings.getSize());
   LineStrings.write((uint8_t *)Data.data());
-  MCOS->emitBinaryData(Data.str());
+  return Data;
 }
 
 void MCDwarfLineStr::emitRef(MCStreamer *MCOS, StringRef Path) {
   int RefSize =
       dwarf::getDwarfOffsetByteSize(MCOS->getContext().getDwarfFormat());
   size_t Offset = LineStrings.add(Path);
   if (UseRelocs) {
     MCContext &Ctx = MCOS->getContext();

llvm/unittests/MC/DwarfLineTableHeaders.cpp

void emitDebugLineSection(StreamerContext &C) {
     MCSymbol *LineEndSym = Header.Emit(TheStreamer, Params, LineStr).second;
 
     // Put out the line tables.
     MCLineSection::MCDwarfLineEntryCollection LineEntries;
     MCDwarfLineEntry LineEntry(LineSym, Loc);
     LineEntries.push_back(LineEntry);
     MCDwarfLineTable::emitOne(TheStreamer, Section, LineEntries);
     TheStreamer->emitLabel(LineEndSym);
-    if (LineStr)
-      LineStr->emitSection(TheStreamer);
+    if (LineStr) {
+      SmallString<0> Data = LineStr->getFinalizedData();
+      TheStreamer->SwitchSection(TheStreamer->getContext()
+                                     .getObjectFileInfo()
+                                     ->getDwarfLineStrSection());
+      TheStreamer->emitBinaryData(Data.str());
+    }
   }
 
   /// Check contents of .debug_line section
   void verifyDebugLineContents(const llvm::object::ObjectFile &E,
                                ArrayRef<uint8_t> ExpectedEncoding) {
     for (const llvm::object::SectionRef &Section : E.sections()) {
       Expected<StringRef> SectionNameOrErr = Section.getName();
       ASSERT_TRUE(static_cast<bool>(SectionNameOrErr));
       StringRef SectionName = *SectionNameOrErr;
       if (SectionName.empty() || SectionName != ".debug_line")
         continue;
       Expected<StringRef> ContentsOrErr = Section.getContents();
       ASSERT_TRUE(static_cast<bool>(ContentsOrErr));
       StringRef Contents = *ContentsOrErr;
       ASSERT_TRUE(Contents.size() > ExpectedEncoding.size());
       EXPECT_EQ(
           arrayRefFromStringRef(Contents.slice(0, ExpectedEncoding.size())),
           ExpectedEncoding);
       return;
     }
     llvm_unreachable(".debug_line not found");
   }
 
+  /// Check contents of .debug_line_str section
+  void verifyDebugLineStrContents(const llvm::object::ObjectFile &E) {
+    for (const llvm::object::SectionRef &Section : E.sections()) {
+      Expected<StringRef> SectionNameOrErr = Section.getName();
+      ASSERT_TRUE(static_cast<bool>(SectionNameOrErr));
+      StringRef SectionName = *SectionNameOrErr;
+      if (SectionName.empty() || SectionName != ".debug_line_str")
+        continue;
+      Expected<StringRef> ContentsOrErr = Section.getContents();
+      ASSERT_TRUE(static_cast<bool>(ContentsOrErr));
+      StringRef Contents = *ContentsOrErr;
+      ASSERT_TRUE(Contents.find("dir") != StringRef::npos);
+      ASSERT_TRUE(Contents.find("file") != StringRef::npos);
+      ASSERT_TRUE(Contents.size() == 9);
+      return;
+    }
+    llvm_unreachable(".debug_line_str not found");
+  }
+
   ///  Open ObjFileData as an object file and read its .debug_line section
-  void readAndCheckDebugLineContents(StringRef ObjFileData,
-                                     ArrayRef<uint8_t> Expected) {
+  void readAndCheckDebugContents(StringRef ObjFileData,
+                                     ArrayRef<uint8_t> Expected, uint8_t DwarfVersion) {
     std::unique_ptr<MemoryBuffer> MB =
         MemoryBuffer::getMemBuffer(ObjFileData, "", false);
     std::unique_ptr<object::Binary> Bin =
         cantFail(llvm::object::createBinary(MB->getMemBufferRef()));
     if (auto *E = dyn_cast<llvm::object::ELFObjectFileBase>(&*Bin)) {
-      return verifyDebugLineContents(*E, Expected);
+      verifyDebugLineContents(*E, Expected);
+      if (DwarfVersion >= 5)
+        verifyDebugLineStrContents(*E);
+      return;
     }
     llvm_unreachable("ELF object file not found");
   }
 };
 } // namespace
 
 TEST_F(DwarfLineTableHeaders, TestDWARF4HeaderEmission) {
   if (!MRI)
     return;
 
   SmallString<0> EmittedBinContents;
   raw_svector_ostream VecOS(EmittedBinContents);
   StreamerContext C = createStreamer(VecOS);
-  C.Ctx->setDwarfVersion(4);
+  constexpr uint8_t DwarfVersion = 4;
+  C.Ctx->setDwarfVersion(DwarfVersion);
   emitDebugLineSection(C);
   C.Streamer->Finish();
-  readAndCheckDebugLineContents(
+  readAndCheckDebugContents(
       EmittedBinContents.str(),
       {/*    Total length=*/0x30, 0, 0, 0,
-       /*   DWARF version=*/4, 0,
+       /*   DWARF version=*/DwarfVersion, 0,
        /* Prologue length=*/0x14, 0, 0, 0,
        /* min_inst_length=*/1,
        /*max_ops_per_inst=*/1,
        /* default_is_stmt=*/DWARF2_LINE_DEFAULT_IS_STMT,
        /*       line_base=*/static_cast<uint8_t>(-5),
        /*      line_range=*/14,
-       /*     opcode_base=*/13});
+       /*     opcode_base=*/13}, DwarfVersion);
 }
 
 TEST_F(DwarfLineTableHeaders, TestDWARF5HeaderEmission) {
   if (!MRI)
     return;
 
   SmallString<0> EmittedBinContents;
   raw_svector_ostream VecOS(EmittedBinContents);
   StreamerContext C = createStreamer(VecOS);
-  C.Ctx->setDwarfVersion(5);
+  constexpr uint8_t DwarfVersion = 5;
+  C.Ctx->setDwarfVersion(DwarfVersion);
   emitDebugLineSection(C);
   C.Streamer->Finish();
-  readAndCheckDebugLineContents(
+  readAndCheckDebugContents(
       EmittedBinContents.str(),
       {/*    Total length=*/0x43, 0, 0, 0,
-       /*   DWARF version=*/5, 0,
+       /*   DWARF version=*/DwarfVersion, 0,
        /*        ptr size=*/8,
        /*         segment=*/0,
        /* Prologue length=*/0x25, 0, 0, 0,
        /* min_inst_length=*/1,
        /*max_ops_per_inst=*/1,
        /* default_is_stmt=*/DWARF2_LINE_DEFAULT_IS_STMT,
        /*       line_base=*/static_cast<uint8_t>(-5),
        /*      line_range=*/14,
-       /*     opcode_base=*/13});
+       /*     opcode_base=*/13}, DwarfVersion);
 }