[BOLT][DWARF] Fix handling of debug_str_offsets (#75100)

We were not setting size field of .debug_str_offsets correctly. Fixed
it, and added a test.

Author: ayermolo

bolt/include/bolt/Core/DebugData.h

@@ -459,8 +459,6 @@ class DebugStrOffsetsWriter {
   std::unique_ptr<raw_svector_ostream> StrOffsetsStream;
   std::map<uint32_t, uint32_t> IndexToAddressMap;
   std::unordered_map<uint64_t, uint64_t> ProcessedBaseOffsets;
-  // Section size not including header.
-  uint32_t CurrentSectionSize{0};
   bool StrOffsetSectionWasModified = false;
 };
 

bolt/lib/Core/DebugData.cpp

@@ -889,8 +889,10 @@ void DebugStrOffsetsWriter::finalizeSection(DWARFUnit &Unit,
   // Handling re-use of str-offsets section.
   if (RetVal == ProcessedBaseOffsets.end() || StrOffsetSectionWasModified) {
     // Writing out the header for each section.
-    support::endian::write(*StrOffsetsStream, CurrentSectionSize + 4,
-                           llvm::endianness::little);
+    support::endian::write(
+        *StrOffsetsStream,
+        static_cast<uint32_t>(IndexToAddressMap.size() * 4 + 4),
+        llvm::endianness::little);
     support::endian::write(*StrOffsetsStream, static_cast<uint16_t>(5),
                            llvm::endianness::little);
     support::endian::write(*StrOffsetsStream, static_cast<uint16_t>(0),

bolt/lib/Rewrite/DWARFRewriter.cpp

@@ -696,8 +696,9 @@ void DWARFRewriter::updateDebugInfo() {
     std::optional<DWARFUnit *> SplitCU;
     std::optional<uint64_t> RangesBase;
     std::optional<uint64_t> DWOId = Unit->getDWOId();
-    StrOffstsWriter->initialize(Unit->getStringOffsetSection(),
-                                Unit->getStringOffsetsTableContribution());
+    if (Unit->getVersion() >= 5)
+      StrOffstsWriter->initialize(Unit->getStringOffsetSection(),
+                                  Unit->getStringOffsetsTableContribution());
     if (DWOId)
       SplitCU = BC.getDWOCU(*DWOId);
     DebugLocWriter *DebugLocWriter = createRangeLocList(*Unit);

bolt/test/X86/dwarf5-two-cu-str-offset-table.test

@@ -0,0 +1,66 @@
+# REQUIRES: system-linux
+
+# RUN: llvm-mc -dwarf-version=5 -filetype=obj -triple x86_64-unknown-linux %p/Inputs/dwarf5_main.s -o %tmain.o
+# RUN: llvm-mc -dwarf-version=5 -filetype=obj -triple x86_64-unknown-linux %p/Inputs/dwarf5_helper.s -o %thelper.o
+# RUN: %clang %cflags -dwarf-5 %tmain.o %thelper.o -o %t.exe -Wl,-q
+# RUN: llvm-bolt %t.exe -o %t.bolt --update-debug-sections
+# RUN: llvm-dwarfdump --show-form --verbose --debug-str-offsets %t.exe > %t.txt
+# RUN: llvm-dwarfdump --show-form --verbose --debug-str-offsets %t.bolt >> %t.txt
+# RUN: cat %t.txt | FileCheck --check-prefix=CHECK %s
+
+## This test checks we correclty re-renerate .debug_str_offsets.
+
+# CHECK: .debug_str_offsets contents
+# CHECK-NEXT: 0x00000000: Contribution size = 52, Format = DWARF32, Version = 5
+# CHECK-NEXT: "clang version 15.0.0"
+# CHECK-NEXT: "main.cpp"
+# CHECK-NEXT: "/testLocListMultiple"
+# CHECK-NEXT: "_Z3usePiS_"
+# CHECK-NEXT: "use"
+# CHECK-NEXT: "main"
+# CHECK-NEXT: "int"
+# CHECK-NEXT: "x"
+# CHECK-NEXT: "y"
+# CHECK-NEXT: "argc"
+# CHECK-NEXT: "argv"
+# CHECK-NEXT: "char"
+# CHECK-NEXT: 0x00000038: Contribution size = 48, Format = DWARF32, Version = 5
+# CHECK-NEXT: "clang version 15.0.0)"
+# CHECK-NEXT: "foo.cpp"
+# CHECK-NEXT: "/testLocListMultiple"
+# CHECK-NEXT: "fooVar"
+# CHECK-NEXT: "int"
+# CHECK-NEXT: "_Z6useFooPi"
+# CHECK-NEXT: "useFoo"
+# CHECK-NEXT: "x"
+# CHECK-NEXT: "_Z3fooi"
+# CHECK-NEXT: "foo"
+# CHECK-NEXT: "argc"
+
+## Checking post bolt
+# CHECK: .debug_str_offsets contents
+# CHECK-NEXT: 0x00000000: Contribution size = 52, Format = DWARF32, Version = 5
+# CHECK-NEXT: "clang version 15.0.0"
+# CHECK-NEXT: "main.cpp"
+# CHECK-NEXT: "/testLocListMultiple"
+# CHECK-NEXT: "_Z3usePiS_"
+# CHECK-NEXT: "use"
+# CHECK-NEXT: "main"
+# CHECK-NEXT: "int"
+# CHECK-NEXT: "x"
+# CHECK-NEXT: "y"
+# CHECK-NEXT: "argc"
+# CHECK-NEXT: "argv"
+# CHECK-NEXT: "char"
+# CHECK-NEXT: 0x00000038: Contribution size = 48, Format = DWARF32, Version = 5
+# CHECK-NEXT: "clang version 15.0.0)"
+# CHECK-NEXT: "foo.cpp"
+# CHECK-NEXT: "/testLocListMultiple"
+# CHECK-NEXT: "fooVar"
+# CHECK-NEXT: "int"
+# CHECK-NEXT: "_Z6useFooPi"
+# CHECK-NEXT: "useFoo"
+# CHECK-NEXT: "x"
+# CHECK-NEXT: "_Z3fooi"
+# CHECK-NEXT: "foo"
+# CHECK-NEXT: "argc"