[llvm] e49584a - [WebAssembly] Fix for use of uninitialized member in WasmObjectWriter.cpp

[Sam Clegg via llvm-commits]

Author: Sam Clegg
Date: 2020-06-23T15:26:18-07:00
New Revision: e49584a34a1242e4f9f0b6e65f19e3cbec43d906

URL: https://github.com/llvm/llvm-project/commit/e49584a34a1242e4f9f0b6e65f19e3cbec43d906
DIFF: https://github.com/llvm/llvm-project/commit/e49584a34a1242e4f9f0b6e65f19e3cbec43d906.diff

LOG: [WebAssembly] Fix for use of uninitialized member in WasmObjectWriter.cpp

Currently, section indices may be passed uninitialized by value if
writing the section fails. Removes section indices form class
initialization and returns them from the write{Code,Data}Section
function calls instead.

Patch by Gui Andrade!

Differential Revision: https://reviews.llvm.org/D81702

Added: 
    

Modified: 
    llvm/lib/MC/WasmObjectWriter.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/MC/WasmObjectWriter.cpp b/llvm/lib/MC/WasmObjectWriter.cpp
index c3f39a7a62ad..c6029b66a388 100644
--- a/llvm/lib/MC/WasmObjectWriter.cpp
+++ b/llvm/lib/MC/WasmObjectWriter.cpp
@@ -224,11 +224,8 @@ class WasmObjectWriter : public MCObjectWriter {
 
   // Relocations for fixing up references in the code section.
   std::vector<WasmRelocationEntry> CodeRelocations;
-  uint32_t CodeSectionIndex;
-
   // Relocations for fixing up references in the data section.
   std::vector<WasmRelocationEntry> DataRelocations;
-  uint32_t DataSectionIndex;
 
   // Index values to use for fixing up call_indirect type indices.
   // Maps function symbols to the index of the type of the function
@@ -335,9 +332,9 @@ class WasmObjectWriter : public MCObjectWriter {
   void writeExportSection(ArrayRef<wasm::WasmExport> Exports);
   void writeElemSection(ArrayRef<uint32_t> TableElems);
   void writeDataCountSection();
-  void writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
-                        ArrayRef<WasmFunction> Functions);
-  void writeDataSection(const MCAsmLayout &Layout);
+  uint32_t writeCodeSection(const MCAssembler &Asm, const MCAsmLayout &Layout,
+                            ArrayRef<WasmFunction> Functions);
+  uint32_t writeDataSection(const MCAsmLayout &Layout);
   void writeEventSection(ArrayRef<wasm::WasmEventType> Events);
   void writeGlobalSection(ArrayRef<wasm::WasmGlobal> Globals);
   void writeRelocSection(uint32_t SectionIndex, StringRef Name,
@@ -894,15 +891,14 @@ void WasmObjectWriter::writeDataCountSection() {
   endSection(Section);
 }
 
-void WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
-                                        const MCAsmLayout &Layout,
-                                        ArrayRef<WasmFunction> Functions) {
+uint32_t WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
+                                            const MCAsmLayout &Layout,
+                                            ArrayRef<WasmFunction> Functions) {
   if (Functions.empty())
-    return;
+    return 0;
 
   SectionBookkeeping Section;
   startSection(Section, wasm::WASM_SEC_CODE);
-  CodeSectionIndex = Section.Index;
 
   encodeULEB128(Functions.size(), W.OS);
 
@@ -922,15 +918,15 @@ void WasmObjectWriter::writeCodeSection(const MCAssembler &Asm,
   applyRelocations(CodeRelocations, Section.ContentsOffset, Layout);
 
   endSection(Section);
+  return Section.Index;
 }
 
-void WasmObjectWriter::writeDataSection(const MCAsmLayout &Layout) {
+uint32_t WasmObjectWriter::writeDataSection(const MCAsmLayout &Layout) {
   if (DataSegments.empty())
-    return;
+    return 0;
 
   SectionBookkeeping Section;
   startSection(Section, wasm::WASM_SEC_DATA);
-  DataSectionIndex = Section.Index;
 
   encodeULEB128(DataSegments.size(), W.OS); // count
 
@@ -952,6 +948,7 @@ void WasmObjectWriter::writeDataSection(const MCAsmLayout &Layout) {
   applyRelocations(DataRelocations, Section.ContentsOffset, Layout);
 
   endSection(Section);
+  return Section.Index;
 }
 
 void WasmObjectWriter::writeRelocSection(
@@ -1698,8 +1695,8 @@ uint64_t WasmObjectWriter::writeObject(MCAssembler &Asm,
   writeExportSection(Exports);
   writeElemSection(TableElems);
   writeDataCountSection();
-  writeCodeSection(Asm, Layout, Functions);
-  writeDataSection(Layout);
+  uint32_t CodeSectionIndex = writeCodeSection(Asm, Layout, Functions);
+  uint32_t DataSectionIndex = writeDataSection(Layout);
   for (auto &CustomSection : CustomSections)
     writeCustomSection(CustomSection, Asm, Layout);
   writeLinkingMetaDataSection(SymbolInfos, InitFuncs, Comdats);