Export symbols used in inline functions

[jbrianceau]

fixed_address_empty_string and default_instance symbols
are used in inline functions. We have to export them properly to
avoid undefined reference link errors.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[grpc-kokoro]

Thanks for your pull request. The automated tests will run as soon as one of the admins verifies this change is ok for us to run on our infrastructure.

[jbrianceau]

Mmm, the change works well in Chromium, but it doesn't seem to work very well here :/

[jbrianceau]

It's better after having regenerated descriptor proto, the windows build is still broken though.

Maybe I should deinline functions instead of trying to export symbol ? What do you think ?

[xfxyjwf]

deinline is usually not an acceptable solution because of its performance impact. Our appveyor already covers DLL build and it's passing without this pull request. Could it be a build setup problem of Chrome?

[jbrianceau]

deinline is usually not an acceptable solution because of its performance impact.

Ok.

Our appveyor already covers DLL build and it's passing without this pull request. Could it be a build setup problem of Chrome?

That's what I do not understand yet : why Windows version builds fine without my patch and fails with it when we use protobuf as a shared library ? (whereas Linux is fine).

For instance :

• we have in src/google/protobuf/generated_message_util.h :

extern ExplicitlyConstructed< ::std::string> fixed_address_empty_string;

LIBPROTOBUF_EXPORT inline const ::std::string& GetEmptyStringAlreadyInited() {
  return fixed_address_empty_string.get();
}

• and in src/google/protobuf/generated_message_util.cc :

ExplicitlyConstructed< ::std::string> fixed_address_empty_string;

So when protobuf is a shared library, the symbol google::protobuf::internal::fixed_address_empty_string is hidden in it :

   115: 00000000000370a0    16 OBJECT  LOCAL  HIDDEN    27 _ZN6google8protobuf8internal26fixed_address_empty_stringE

So when a piece of code from another module includes generated_message_util.h and links with protobuf shared library, there is an undefined reference to google::protobuf::internal::fixed_address_empty_string as the symbol is hidden.

Am I missing something here ?

[thirdknife]

I am unable to build version 3.1.0 on windows with MSVS CE 2015. Getting an unresolved external symbol on:

LNK2001 unresolved external symbol "class google::protobuf::internal::ExplicitlyConstructed<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > google::protobuf::internal::fixed_address_empty_string" (?fixed_address_empty_string@internal@protobuf@google@@3V?$ExplicitlyConstructed@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@123@A)

and

LNK2001 unresolved external symbol "__int64 google::protobuf::internal::empty_string_once_init_" (?empty_string_once_init_@internal@protobuf@google@@3_JA)

Any hints where I can look into to fix the source?

[jbrianceau]

Does this pull request fix your issue @thirdknife ? Especially this commit : 8a07630

[thirdknife]

This fails the protobuf build with the following error:

google::protobuf::internal::fixed_address_empty_string': redefinition; different storage class libprotobuf

[jbrianceau]

I made the mistake of exporting the symbol definition in the source file instead of exporting its declaration in the header file.
@xfxyjwf, I have rebased the change and hopefully fixed the issue.

[jbrianceau]

Follow-up : #2462