Don't allow multiple symbol tables in the module block.

src/PNaClTranslator.cpp

@@ -3010,6 +3010,8 @@ private:
   // True if we have already installed names for unnamed global declarations,
   // and have generated global constant initializers.
   bool GlobalDeclarationNamesAndInitializersInstalled = false;
+  // True if we have already processed the symbol table for the module.
+  bool FoundValuesymtab = false;
 
   // Generates names for unnamed global addresses (i.e. functions and global
   // variables). Then lowers global variable declaration initializers to the
@@ -3019,7 +3021,10 @@ private:
     if (!GlobalDeclarationNamesAndInitializersInstalled) {
       Context->installGlobalNames();
       Context->createValueIDs();
-      getTranslator().lowerGlobals(Context->getGlobalVariables());
+      std::unique_ptr<Ice::VariableDeclarationList> Globals =
+          Context->getGlobalVariables();
+      if (Globals)
+        getTranslator().lowerGlobals(std::move(Globals));
       GlobalDeclarationNamesAndInitializersInstalled = true;
     }
   }
@@ -3074,6 +3079,10 @@ bool ModuleParser::ParseBlock(unsigned BlockID) {
     return Parser.ParseThisBlock();
   }
   case naclbitc::VALUE_SYMTAB_BLOCK_ID: {
+    if (FoundValuesymtab)
+      Fatal("Duplicate valuesymtab in module");
+
+    FoundValuesymtab = true;
     ModuleValuesymtabParser Parser(BlockID, this);
     return Parser.ParseThisBlock();
   }

tests_lit/parse_errs/Inputs/dup-module-vst.tbc

+65535,8,2;
+1,1;
+65535,17,2;
+1,2;
+2;
+21,0,0;
+65534;
+8,1,0,0,0;
+65535,19,2;
+5,0;
+65534;
+65535,14,2;
+1,0,102;
+65534;
+65535,14,2;
+1,0,102;
+65534;
+65535,12,2;
+1,1;
+10;
+65534;
+65534;

tests_lit/parse_errs/dup-module-vst.test

+; Test if we detect multiple module-level symbol tables in bitcode.
+
+; REQUIRES: no_minimal_build
+
+; RUN: not %pnacl_sz -bitcode-as-text %p/Inputs/dup-module-vst.tbc \
+; RUN:     -bitcode-format=pnacl -notranslate -build-on-read 2>&1 \
+; RUN:   | FileCheck %s
+
+; CHECK: Duplicate valuesymtab in module
+
+; RUN: pnacl-bcfuzz -bitcode-as-text %p/Inputs/dup-module-vst.tbc \
+; RUN:   -output - | pnacl-bcdis -no-records | FileCheck -check-prefix=ASM %s
+
+; ASM: module {  // BlockID = 8
+; ASM:   valuesymtab {  // BlockID = 14
+; ASM:     @f0 : "f";
+; ASM:   }
+; ASM:   valuesymtab {  // BlockID = 14
+; ASM:     @f0 : "f";
+; ASM:   }
+; ASM: }
+