[XCOFF] make sure same number of paddings are added for DWARF sections

We are going to change alignment for DWARF sections. This patch is to
fix functionality issue if the alignment is not the same with
DefaultSectionAlign defined in XCOFFObjectWriter.cpp.

Currently no test for this patch as for now alignment for DWARF sections
and other sections are always the same. This patch will be tested when
patch changing DWARF section is merged in.

Reviewed By: Esme

Differential Revision: https://reviews.llvm.org/D116092

llvm/lib/MC/XCOFFObjectWriter.cpp

@@ -180,9 +180,14 @@ struct DwarfSectionEntry : public SectionEntry {
   // For DWARF section entry.
   std::unique_ptr<XCOFFSection> DwarfSect;
 
+  // For DWARF section, we must use real size in the section header. MemorySize
+  // is for the size the DWARF section occupies including paddings.
+  uint32_t MemorySize;
+
   DwarfSectionEntry(StringRef N, int32_t Flags,
                     std::unique_ptr<XCOFFSection> Sect)
-      : SectionEntry(N, Flags | XCOFF::STYP_DWARF), DwarfSect(std::move(Sect)) {
+      : SectionEntry(N, Flags | XCOFF::STYP_DWARF), DwarfSect(std::move(Sect)),
+        MemorySize(0) {
     assert(DwarfSect->MCSec->isDwarfSect() &&
            "This should be a DWARF section!");
     assert(N.size() <= XCOFF::NameSize && "section name too long");
@@ -982,6 +987,7 @@ void XCOFFObjectWriter::assignAddressesAndIndices(const MCAsmLayout &Layout) {
   // Section indices are 1-based in XCOFF.
   int32_t SectionIndex = 1;
   bool HasTDataSection = false;
+  uint32_t PaddingsBeforeDwarf = 0;
 
   for (auto *Section : Sections) {
     const bool IsEmpty =
@@ -1041,6 +1047,19 @@ void XCOFFObjectWriter::assignAddressesAndIndices(const MCAsmLayout &Layout) {
     Section->Size = Address - Section->Address;
   }
 
+  // Start to generate DWARF sections. Sections other than DWARF section use
+  // DefaultSectionAlign as the default alignment, while DWARF sections have
+  // their own alignments. If these two alignments are not the same, we need
+  // some paddings here and record the paddings bytes for FileOffsetToData
+  // calculation.
+  if (!DwarfSections.empty())
+    PaddingsBeforeDwarf =
+        alignTo(Address,
+                (*DwarfSections.begin()).DwarfSect->MCSec->getAlignment()) -
+        Address;
+
+  DwarfSectionEntry *LastDwarfSection = nullptr;
+
   for (auto &DwarfSection : DwarfSections) {
     assert((SectionIndex <= MaxSectionIndex) && "Section index overflow!");
 
@@ -1068,8 +1087,19 @@ void XCOFFObjectWriter::assignAddressesAndIndices(const MCAsmLayout &Layout) {
     // For DWARF section, we must use the real size which may be not aligned.
     DwarfSection.Size = DwarfSect.Size = Layout.getSectionAddressSize(MCSec);
 
-    // Make the Address align to default alignment for follow section.
-    Address = alignTo(DwarfSect.Address + DwarfSect.Size, DefaultSectionAlign);
+    Address = DwarfSection.Address + DwarfSection.Size;
+
+    if (LastDwarfSection)
+      LastDwarfSection->MemorySize =
+          DwarfSection.Address - LastDwarfSection->Address;
+    LastDwarfSection = &DwarfSection;
+  }
+  if (LastDwarfSection) {
+    // Make the final DWARF section address align to the default section
+    // alignment for follow contents.
+    Address = alignTo(LastDwarfSection->Address + LastDwarfSection->Size,
+                      DefaultSectionAlign);
+    LastDwarfSection->MemorySize = Address - LastDwarfSection->Address;
   }
 
   SymbolTableEntryCount = SymbolTableIndex;
@@ -1092,19 +1122,15 @@ void XCOFFObjectWriter::assignAddressesAndIndices(const MCAsmLayout &Layout) {
       report_fatal_error("Section raw data overflowed this object file.");
   }
 
-  for (auto &DwarfSection : DwarfSections) {
-    // Address of csect sections are always aligned to DefaultSectionAlign, but
-    // address of DWARF section are aligned to Section alignment which may be
-    // bigger than DefaultSectionAlign, need to execlude the padding bits.
-    RawPointer =
-        alignTo(RawPointer, DwarfSection.DwarfSect->MCSec->getAlignment());
+  // Increase the raw pointer for the padding bytes between csect sections and
+  // DWARF sections.
+  if (!DwarfSections.empty())
+    RawPointer += PaddingsBeforeDwarf;
 
+  for (auto &DwarfSection : DwarfSections) {
     DwarfSection.FileOffsetToData = RawPointer;
-    // Some section entries, like DWARF section size is not aligned, so
-    // RawPointer may be not aligned.
-    RawPointer += DwarfSection.Size;
-    // Make sure RawPointer is aligned.
-    RawPointer = alignTo(RawPointer, DefaultSectionAlign);
+
+    RawPointer += DwarfSection.MemorySize;
 
     assert(RawPointer <= MaxRawDataSize &&
            "Section raw data overflowed this object file.");