[mach-o] zero-fill sections have no file offset

In mach-o, sections of type S_ZEROFILL are special cased and to always have
their section.offset field be zero.

llvm-svn: 222202

3 files changed, 24 insertions, 13 deletions

diff --git a/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp b/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
index 102b185df52..3bc341ffa3a 100644
--- a/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
+++ b/lld/lib/ReaderWriter/MachO/MachONormalizedFileBinaryWriter.cpp
@@ -284,15 +284,21 @@ MachOFileLayout::MachOFileLayout(const NormalizedFile &file)
       _endOfLoadCommands += sizeof(linkedit_data_command);
       _countOfLoadCommands++;
     }
-    // Accumulate size of each section.
+    // Assign file offsets to each section.
     _startOfSectionsContent = _endOfLoadCommands;
-    _endOfSectionsContent = _startOfSectionsContent;
     unsigned relocCount = 0;
+    uint64_t offset = _startOfSectionsContent;
     for (const Section &sect : file.sections) {
-      _sectInfo[&sect].fileOffset = _endOfSectionsContent;
-      _endOfSectionsContent += sect.content.size();
+      if (sect.type != llvm::MachO::S_ZEROFILL) {
+        offset = llvm::RoundUpToAlignment(offset, 1 << sect.alignment);
+        _sectInfo[&sect].fileOffset = offset;
+        offset += sect.content.size();
+      } else {
+        _sectInfo[&sect].fileOffset = 0;
+      }
       relocCount += sect.relocations.size();
     }
+    _endOfSectionsContent = offset;
 
     computeSymbolTableSizes();
     computeDataInCodeSize();
@@ -580,7 +586,8 @@ std::error_code MachOFileLayout::writeSingleSegmentLoadCommand(uint8_t *&lc) {
   uint8_t *next = lc + seg->cmdsize;
   memset(seg->segname, 0, 16);
   seg->vmaddr = 0;
-  seg->vmsize = _endOfSectionsContent - _endOfLoadCommands;
+  seg->vmsize = _file.sections.back().address
+              + _file.sections.back().content.size();
   seg->fileoff = _endOfLoadCommands;
   seg->filesize = seg->vmsize;
   seg->maxprot = VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE;
@@ -592,14 +599,13 @@ std::error_code MachOFileLayout::writeSingleSegmentLoadCommand(uint8_t *&lc) {
   typename T::section *sout = reinterpret_cast<typename T::section*>
                                               (lc+sizeof(typename T::command));
   uint32_t relOffset = _startOfRelocations;
-  uint32_t contentOffset = _startOfSectionsContent;
   uint32_t indirectSymRunningIndex = 0;
   for (const Section &sin : _file.sections) {
     setString16(sin.sectionName, sout->sectname);
     setString16(sin.segmentName, sout->segname);
     sout->addr = sin.address;
     sout->size = sin.content.size();
-    sout->offset = contentOffset;
+    sout->offset = _sectInfo[&sin].fileOffset;
     sout->align = sin.alignment;
     sout->reloff = sin.relocations.empty() ? 0 : relOffset;
     sout->nreloc = sin.relocations.size();
@@ -607,7 +613,6 @@ std::error_code MachOFileLayout::writeSingleSegmentLoadCommand(uint8_t *&lc) {
     sout->reserved1 = indirectSymbolIndex(sin, indirectSymRunningIndex);
     sout->reserved2 = indirectSymbolElementSize(sin);
     relOffset += sin.relocations.size() * sizeof(any_relocation_info);
-    contentOffset += sin.content.size();
     if (_swap)
       swapStruct(*sout);
     ++sout;
@@ -645,7 +650,10 @@ std::error_code MachOFileLayout::writeSegmentLoadCommands(uint8_t *&lc) {
       setString16(section->segmentName, sect->segname);
       sect->addr      = section->address;
       sect->size      = section->content.size();
-      sect->offset    = section->address - seg.address + segInfo.fileOffset;
+      if (section->type == llvm::MachO::S_ZEROFILL)
+        sect->offset  = 0;
+      else
+        sect->offset  = section->address - seg.address + segInfo.fileOffset;
       sect->align     = section->alignment;
       sect->reloff    = 0;
       sect->nreloc    = 0;
diff --git a/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp b/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
index 780c9c02fc8..a668dadb129 100644
--- a/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
+++ b/lld/lib/ReaderWriter/MachO/MachONormalizedFileFromAtoms.cpp
@@ -573,11 +573,14 @@ void Util::copySectionContent(NormalizedFile &file) {
   };
 
   for (SectionInfo *si : _sectionInfos) {
-    if (si->type == llvm::MachO::S_ZEROFILL)
+    Section *normSect = &file.sections[si->normalizedSectionIndex];
+    if (si->type == llvm::MachO::S_ZEROFILL) {
+      const uint8_t *empty = nullptr;
+      normSect->content = llvm::makeArrayRef(empty, si->size);
       continue;
+    }
     // Copy content from atoms to content buffer for section.
     uint8_t *sectionContent = file.ownedAllocations.Allocate<uint8_t>(si->size);
-    Section *normSect = &file.sections[si->normalizedSectionIndex];
     normSect->content = llvm::makeArrayRef(sectionContent, si->size);
     for (AtomInfo &ai : si->atomsAndOffsets) {
       uint8_t *atomContent = reinterpret_cast<uint8_t*>
diff --git a/lld/test/mach-o/exe-offsets.yaml b/lld/test/mach-o/exe-offsets.yaml
index 4ab4faba308..a751507432e 100644
--- a/lld/test/mach-o/exe-offsets.yaml
+++ b/lld/test/mach-o/exe-offsets.yaml
@@ -41,5 +41,5 @@ defined-atoms:
 # CHECK-LABEL: Section {
 # CHECK:     Name: __bss
 # CHECK:     Segment: __DATA
-# CHECK:     Size: 0x0
-# CHECK:     Offset: 4101
+# CHECK:     Size: 0x2064
+# CHECK:     Offset: 0