[WebAssembly] Support VPtr sanitizer for Emscripten

[quantum]

Summary

After https://github.com/emscripten-core/emscripten/pull/8651, Emscripten
supports the full UBSan runtime. This includes the VPtr sanitizer.

This diff allows clang to generate code that uses the VPtr sanitizer for
Emscripten.

[aheejin]

clang/lib/Driver/ToolChains/WebAssembly.cpp

214

Does this mean we only support Vptr among sanitizers here?

[tlively]

Please add a test!

[quantum]

clang/lib/Driver/ToolChains/WebAssembly.cpp

214

No, by default all of UBSan except Vptr and Function are declared as supported. This adds Vptr to the list as it's supported on Emscripten.

[aheejin]

clang/lib/Driver/ToolChains/WebAssembly.cpp

214

I see. By the way where do we say we support the undefined sanitizer group?

[quantum]

Add a test

[quantum]

clang/lib/Driver/ToolChains/WebAssembly.cpp

214

The base ToolChain class says it's supported on all platforms.

[aheejin]

clang/lib/Driver/ToolChains/WebAssembly.cpp

214

By the way this seems to include Vptr as well..? Am I looking at the wrong place?

[aheejin]

clang/lib/Driver/ToolChains/WebAssembly.cpp

214

Oh nevermind, the base method explicitly excludes Vptr and Function.

clang/lib/Driver/ToolChains/WebAssembly.h

private:
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
   void AddClangCXXStdlibIncludeArgs(
       const llvm::opt::ArgList &DriverArgs,
       llvm::opt::ArgStringList &CC1Args) const override;
   void AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs) const override;
+  SanitizerMask getSupportedSanitizers() const override;
 
   const char *getDefaultLinker() const override { return "wasm-ld"; }
 
   Tool *buildLinker() const override;
 };
 
 } // end namespace toolchains
 } // end namespace driver
 } // end namespace clang
 
 #endif // LLVM_CLANG_LIB_DRIVER_TOOLCHAINS_WEBASSEMBLY_H

clang/lib/Driver/ToolChains/WebAssembly.cpp

case ToolChain::CST_Libcxx:
     CmdArgs.push_back("-lc++");
     CmdArgs.push_back("-lc++abi");
     break;
   case ToolChain::CST_Libstdcxx:
     llvm_unreachable("invalid stdlib name");
   }
 }
 
+SanitizerMask WebAssembly::getSupportedSanitizers() const {
+  SanitizerMask Res = ToolChain::getSupportedSanitizers();
+  if (getTriple().isOSEmscripten()) {
+    Res |= SanitizerKind::Vptr;
+  }
+  return Res;
+}
+
 Tool *WebAssembly::buildLinker() const {
   return new tools::wasm::Linker(*this);
 }

clang/test/CodeGenCXX/wasm-sanitize-vptr.cpp

+// RUN: %clang_cc1 -std=c++11 -fsanitize=vptr -emit-llvm %s -o - -triple wasm32-unknown-emscripten | FileCheck %s
+
+struct S {
+  virtual ~S() {}
+  int a;
+};
+
+struct T : S {
+  int b;
+};
+
+// CHECK-LABEL: @_Z15bad_static_castv
+void bad_static_cast() {
+  S s;
+  // CHECK: br i1 %[[NONNULL:.*]], label %[[CONT:.*]], label %[[MISS:.*]], !prof
+  // CHECK: [[MISS]]:
+  // CHECK: call void @__ubsan_handle_dynamic_type_cache_miss_abort
+  // CHECK: [[CONT]]:
+  T &r = static_cast<T &>(s);
+}