[WebAssembly] Add data size and alignement to linking section

The overal size of the data section (including BSS)
is otherwise not included in the wasm binary.

Differential Revision: https://reviews.llvm.org/D34657

llvm-svn: 306459

3 files changed, 29 insertions, 8 deletions

diff --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp
index 45534ba1821..82352cb50c7 100644
--- a/llvm/lib/MC/WasmObjectWriter.cpp
+++ b/llvm/lib/MC/WasmObjectWriter.cpp
@@ -265,7 +265,8 @@ private:
                         uint32_t NumFuncImports);
   void writeCodeRelocSection();
   void writeDataRelocSection(uint64_t DataSectionHeaderSize);
-  void writeLinkingMetaDataSection(ArrayRef<StringRef> WeakSymbols,
+  void writeLinkingMetaDataSection(uint32_t DataSize, uint32_t DataAlignment,
+                                   ArrayRef<StringRef> WeakSymbols,
                                    bool HasStackPointer,
                                    uint32_t StackPointerGlobal);
 
@@ -877,11 +878,8 @@ void WasmObjectWriter::writeDataRelocSection(uint64_t DataSectionHeaderSize) {
 }
 
 void WasmObjectWriter::writeLinkingMetaDataSection(
-    ArrayRef<StringRef> WeakSymbols, bool HasStackPointer,
-    uint32_t StackPointerGlobal) {
-  if (!HasStackPointer && WeakSymbols.empty())
-    return;
-
+    uint32_t DataSize, uint32_t DataAlignment, ArrayRef<StringRef> WeakSymbols,
+    bool HasStackPointer, uint32_t StackPointerGlobal) {
   SectionBookkeeping Section;
   startSection(Section, wasm::WASM_SEC_CUSTOM, "linking");
   SectionBookkeeping SubSection;
@@ -902,6 +900,16 @@ void WasmObjectWriter::writeLinkingMetaDataSection(
     endSection(SubSection);
   }
 
+  if (DataSize > 0) {
+    startSection(SubSection, wasm::WASM_DATA_SIZE);
+    encodeULEB128(DataSize, getStream());
+    endSection(SubSection);
+
+    startSection(SubSection, wasm::WASM_DATA_ALIGNMENT);
+    encodeULEB128(DataAlignment, getStream());
+    endSection(SubSection);
+  }
+
   endSection(Section);
 }
 
@@ -923,6 +931,7 @@ void WasmObjectWriter::writeObject(MCAssembler &Asm,
   unsigned NumFuncImports = 0;
   unsigned NumGlobalImports = 0;
   SmallVector<char, 0> DataBytes;
+  uint32_t DataAlignment = 1;
   uint32_t StackPointerGlobal = 0;
   bool HasStackPointer = false;
 
@@ -1157,6 +1166,7 @@ void WasmObjectWriter::writeObject(MCAssembler &Asm,
         report_fatal_error("data sections must contain at most one variable");
 
       DataBytes.resize(alignTo(DataBytes.size(), DataSection.getAlignment()));
+      DataAlignment = std::max(DataAlignment, DataSection.getAlignment());
 
       DataSection.setSectionOffset(DataBytes.size());
 
@@ -1272,7 +1282,7 @@ void WasmObjectWriter::writeObject(MCAssembler &Asm,
   writeNameSection(Functions, Imports, NumFuncImports);
   writeCodeRelocSection();
   writeDataRelocSection(DataSectionHeaderSize);
-  writeLinkingMetaDataSection(WeakSymbols, HasStackPointer, StackPointerGlobal);
+  writeLinkingMetaDataSection(DataBytes.size(), DataAlignment, WeakSymbols, HasStackPointer, StackPointerGlobal);
 
   // TODO: Translate the .comment section to the output.
   // TODO: Translate debug sections to the output.
diff --git a/llvm/lib/Object/WasmObjectFile.cpp b/llvm/lib/Object/WasmObjectFile.cpp
index d15860674ae..e87dd48cb01 100644
--- a/llvm/lib/Object/WasmObjectFile.cpp
+++ b/llvm/lib/Object/WasmObjectFile.cpp
@@ -193,6 +193,9 @@ static Error readSection(WasmSection &Section, const uint8_t *&Ptr,
 
 WasmObjectFile::WasmObjectFile(MemoryBufferRef Buffer, Error &Err)
     : ObjectFile(Binary::ID_Wasm, Buffer) {
+  LinkingData.DataAlignment = 0;
+  LinkingData.DataSize = 0;
+
   ErrorAsOutParameter ErrAsOutParam(&Err);
   Header.Magic = getData().substr(0, 4);
   if (Header.Magic != StringRef("\0asm", 4)) {
@@ -305,7 +308,7 @@ Error WasmObjectFile::parseLinkingSection(const uint8_t *Ptr,
         auto iter = SymbolMap.find(Symbol);
         if (iter == SymbolMap.end()) {
           return make_error<GenericBinaryError>(
-              "Invalid symbol name in linking section",
+              "Invalid symbol name in linking section: " + Symbol,
               object_error::parse_failed);
         }
         uint32_t SymIndex = iter->second;
@@ -318,6 +321,12 @@ Error WasmObjectFile::parseLinkingSection(const uint8_t *Ptr,
       }
       break;
     }
+    case wasm::WASM_DATA_SIZE:
+      LinkingData.DataSize = readVaruint32(Ptr);
+      break;
+    case wasm::WASM_DATA_ALIGNMENT:
+      LinkingData.DataAlignment = readVaruint32(Ptr);
+      break;
     case wasm::WASM_STACK_POINTER:
     default:
       Ptr += Size;
diff --git a/llvm/lib/ObjectYAML/WasmYAML.cpp b/llvm/lib/ObjectYAML/WasmYAML.cpp
index 65703c6cf68..11999559d65 100644
--- a/llvm/lib/ObjectYAML/WasmYAML.cpp
+++ b/llvm/lib/ObjectYAML/WasmYAML.cpp
@@ -56,6 +56,8 @@ static void sectionMapping(IO &IO, WasmYAML::NameSection &Section) {
 static void sectionMapping(IO &IO, WasmYAML::LinkingSection &Section) {
   commonSectionMapping(IO, Section);
   IO.mapRequired("Name", Section.Name);
+  IO.mapRequired("DataSize", Section.DataSize);
+  IO.mapRequired("DataAlignment", Section.DataAlignment);
   IO.mapRequired("SymbolInfo", Section.SymbolInfos);
 }