XFAIL one sanitizer symbolizer test for FreeBSD

[dim]

Summary

Due to a QoI issuse in FreeBSD's libcxxrt-based demangler, one sanitizer
symbolizer test consistently appears to fail:

Value of: DemangleSwiftAndCXX("foo")
  Actual: "float"
Expected: "foo"

This is because libcxxrt's __cxa_demangle() incorrectly demangles the "foo"
identifier to "float". It should return an error instead.

For now, XFAIL this particular test for FreeBSD, until we can fix libcxxrt
properly (which might take some time to coordinate with upstream).

[emaste]

There's also an issue here in the sanitizer: what DemangleSwiftAndCXX("f") should return is ambiguous. But this makes sense in the interim.

[dim]

In D23001#501701, @emaste wrote:

There's also an issue here in the sanitizer: what DemangleSwiftAndCXX("f") should return is ambiguous.

Both on FreeBSD, Linux and OSX calling __cxa_demangle() with "f" always returns "float". So I guess that is at least a de facto 'correct' result.

As far as I can see in asan and ubsan, where the demangler is called, it always uses external knowledge about the symbol to see whether it should be demangled at all. For instance, lib/asan/asan_report.cc's MaybeDemangleGlobalName():

static const char *MaybeDemangleGlobalName(const char *name) {
  // We can spoil names of globals with C linkage, so use an heuristic
  // approach to check if the name should be demangled.
  bool should_demangle = false;
  if (name[0] == '_' && name[1] == 'Z')
    should_demangle = true;
  else if (SANITIZER_WINDOWS && name[0] == '\01' && name[1] == '?')
    should_demangle = true;

  return should_demangle ? Symbolizer::GetOrInit()->Demangle(name) : name;
}

[zaks.anna]

Maybe it makes sense to change the test to detangle something other than "foo"?

lib/sanitizer_common/tests/sanitizer_symbolizer_test.cc

 
 #if !SANITIZER_WINDOWS
 TEST(Symbolizer, DemangleSwiftAndCXX) {
   // Swift names are not demangled in default llvm build because Swift
   // runtime is not linked in.
   EXPECT_STREQ("_TtSd", DemangleSwiftAndCXX("_TtSd"));
   // Check that the rest demangles properly.
   EXPECT_STREQ("f1(char*, int)", DemangleSwiftAndCXX("_Z2f1Pci"));
+#if !SANITIZER_FREEBSD // QoI issue with libcxxrt on FreeBSD
   EXPECT_STREQ("foo", DemangleSwiftAndCXX("foo"));
+#endif
   EXPECT_STREQ("", DemangleSwiftAndCXX(""));
 }
 #endif
 
 }  // namespace __sanitizer