[WebAssembly] Prevent data inside text sections in assembly

This is not supported in Wasm, unless the data was encoded instructions, but that wouldn't work with the assembler's other functionality (enforcing nesting etc.).

Fixes: https://bugs.llvm.org/show_bug.cgi?id=48971

Differential Revision: https://reviews.llvm.org/D95838

llvm/include/llvm/MC/MCSymbolWasm.h

@@ -14,7 +14,7 @@
 namespace llvm {
 
 class MCSymbolWasm : public MCSymbol {
-  wasm::WasmSymbolType Type = wasm::WASM_SYMBOL_TYPE_DATA;
+  Optional<wasm::WasmSymbolType> Type;
   bool IsWeak = false;
   bool IsHidden = false;
   bool IsComdat = false;
@@ -41,12 +41,15 @@ public:
   void setSize(const MCExpr *SS) { SymbolSize = SS; }
 
   bool isFunction() const { return Type == wasm::WASM_SYMBOL_TYPE_FUNCTION; }
-  bool isData() const { return Type == wasm::WASM_SYMBOL_TYPE_DATA; }
+  // Data is the default value if not set.
+  bool isData() const { return !Type || Type == wasm::WASM_SYMBOL_TYPE_DATA; }
   bool isGlobal() const { return Type == wasm::WASM_SYMBOL_TYPE_GLOBAL; }
   bool isTable() const { return Type == wasm::WASM_SYMBOL_TYPE_TABLE; }
   bool isSection() const { return Type == wasm::WASM_SYMBOL_TYPE_SECTION; }
   bool isEvent() const { return Type == wasm::WASM_SYMBOL_TYPE_EVENT; }
-  wasm::WasmSymbolType getType() const { return Type; }
+
+  Optional<wasm::WasmSymbolType> getType() const { return Type; }
+
   void setType(wasm::WasmSymbolType type) { Type = type; }
 
   bool isExported() const {

llvm/lib/MC/WasmObjectWriter.cpp

@@ -488,10 +488,14 @@ void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
 
     const MCSymbol *SectionSymbol = nullptr;
     const MCSection &SecA = SymA->getSection();
-    if (SecA.getKind().isText())
-      SectionSymbol = SectionFunctions.find(&SecA)->second;
-    else
+    if (SecA.getKind().isText()) {
+      auto SecSymIt = SectionFunctions.find(&SecA);
+      if (SecSymIt == SectionFunctions.end())
+        report_fatal_error("section doesn\'t have defining symbol");
+      SectionSymbol = SecSymIt->second;
+    } else {
       SectionSymbol = SecA.getBeginSymbol();
+    }
     if (!SectionSymbol)
       report_fatal_error("section symbol is required for relocation");
 
@@ -1458,8 +1462,10 @@ uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
         continue;
 
       const auto &WS = static_cast<const MCSymbolWasm &>(S);
-      LLVM_DEBUG(
-          dbgs() << "MCSymbol: " << toString(WS.getType()) << " '" << S << "'"
+      LLVM_DEBUG(dbgs()
+                 << "MCSymbol: "
+                 << toString(WS.getType().getValueOr(wasm::WASM_SYMBOL_TYPE_DATA))
+                 << " '" << S << "'"
                  << " isDefined=" << S.isDefined() << " isExternal="
                  << S.isExternal() << " isTemporary=" << S.isTemporary()
                  << " isWeak=" << WS.isWeak() << " isHidden=" << WS.isHidden()
@@ -1699,7 +1705,7 @@ uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
 
     wasm::WasmSymbolInfo Info;
     Info.Name = WS.getName();
-    Info.Kind = WS.getType();
+    Info.Kind = WS.getType().getValueOr(wasm::WASM_SYMBOL_TYPE_DATA);
     Info.Flags = Flags;
     if (!WS.isData()) {
       assert(WasmIndices.count(&WS) > 0);

llvm/lib/Target/WebAssembly/AsmParser/WebAssemblyAsmParser.cpp

@@ -999,6 +999,20 @@ public:
   }
 
   void doBeforeLabelEmit(MCSymbol *Symbol) override {
+    // Code below only applies to labels in text sections.
+    auto CWS = cast<MCSectionWasm>(getStreamer().getCurrentSection().first);
+    if (!CWS || !CWS->getKind().isText())
+      return;
+
+    auto WasmSym = cast<MCSymbolWasm>(Symbol);
+    // Unlike other targets, we don't allow data in text sections (labels
+    // declared with .type @object).
+    if (WasmSym->getType() == wasm::WASM_SYMBOL_TYPE_DATA) {
+      Parser.Error(Parser.getTok().getLoc(),
+                   "Wasm doesn\'t support data symbols in text sections");
+      return;
+    }
+
     // Start a new section for the next function automatically, since our
     // object writer expects each function to have its own section. This way
     // The user can't forget this "convention".
@@ -1006,14 +1020,10 @@ public:
     if (SymName.startswith(".L"))
       return; // Local Symbol.
 
-    // Only create a new text section if we're already in one.
     // TODO: If the user explicitly creates a new function section, we ignore
     // its name when we create this one. It would be nice to honor their
     // choice, while still ensuring that we create one if they forget.
     // (that requires coordination with WasmAsmParser::parseSectionDirective)
-    auto CWS = cast<MCSectionWasm>(getStreamer().getCurrentSection().first);
-    if (!CWS || !CWS->getKind().isText())
-      return;
     auto SecName = ".text." + SymName;
 
     auto *Group = CWS->getGroup();
@@ -1022,7 +1032,7 @@ public:
     // for importing comdat functions. But there's no way to specify that in
     // assembly currently.
     if (Group)
-      cast<MCSymbolWasm>(Symbol)->setComdat(true);
+      WasmSym->setComdat(true);
     auto *WS =
         getContext().getWasmSection(SecName, SectionKind::getText(), Group,
                                     MCContext::GenericSectionID, nullptr);

llvm/test/MC/WebAssembly/basic-assembly-errors.s

@@ -4,6 +4,10 @@
 # (must be 0.0 or similar)
     f32.const 0
 
+# CHECK: Wasm doesn't support data symbols in text sections
+	.type	objerr,@object
+objerr:
+
 # CHECK: End of block construct with no start: end_try
     end_try
 test0: