[Bug c++/59364] New: C++11 extern thread_local breaks linking: undefined reference to TLS init function

[Bug c++/59364] New: C++11 extern thread_local breaks linking: undefined reference to TLS init function

[conradsand.arma at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59364

            Bug ID: 59364
           Summary: C++11 extern thread_local breaks linking: undefined
                    reference to TLS init function
           Product: gcc
           Version: 4.8.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: conradsand.arma at gmail dot com

Short description:

Declaring a variable as extern thread_local in a C++11 program leads to
"undefined reference to `TLS init function for ..." during linking.

Long description:

Consider three files: rng.hpp, a.cpp and b.cpp, listed below.
Compile using:
g++ a.cpp -c -o a.o -std=c++11
g++ b.cpp -c -o b.o -std=c++11
g++ a.o b.o -o prog -std=c++11

b.o: In function `TLS wrapper function for rng_instance':
b.cpp:(.text._ZTW12rng_instance[_ZTW12rng_instance]+0x5): undefined reference
to `TLS init function for rng_instance'

Things only work if thread_local is removed.

gcc version 4.8.2 20131017 (Red Hat 4.8.2-1) on Fedora 19 (x86-64).

---
rng.hpp:

#include <random>

class rng {
  public:
  std::mt19937_64 engine;
  std::uniform_real_distribution<double> distr;
  double get_val() { return distr(engine); }
  };

---
a.cpp:

#include "rng.hpp"
thread_local rng rng_instance;

---
b.cpp:

#include <iostream>
#include "rng.hpp"

extern thread_local rng rng_instance;

int main(int argc, char** argv)
  {
  std::cout << "val: " << rng_instance.get_val() << std::endl;
  return 0;
  }
---

[Bug c++/59364] C++11 extern thread_local breaks linking: undefined reference to TLS init function

[decaluwe.t at gmail dot com]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59364

Tom De Caluwé <decaluwe.t at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |decaluwe.t at gmail dot com

--- Comment #1 from Tom De Caluwé <decaluwe.t at gmail dot com> ---
This seems to be a duplicate of bug #55800. The workaround mentioned in the
comments fixes the problem.
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[Bug c++/59364] C++11 extern thread_local breaks linking: undefined reference to TLS init function

[conradsand.arma at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59364

--- Comment #2 from Conrad <conradsand.arma at gmail dot com> ---
I wouldn't call the method presented in the comments to bug #55800 as a
workaround.

Quote:
"at least adding .globl  _ZTWN3xyz3blaE _ZTWN3xyz3blaE = __tls_init manually at
the end of the assembly seems to make the code do what it is supposed to"

Editing the assembly is not a workaround -- it's a one off hack.

[Bug c++/59364] C++11 extern thread_local breaks linking: undefined reference to TLS init function

[conradsand.arma at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59364

--- Comment #4 from Conrad <conradsand.arma at gmail dot com> ---
Created attachment 31406
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31406&action=edit
reduced test case

Attached reduced_test_case.tar.gz

No need for pre-processed input, as it doesn't include any system headers.

[Bug c++/59364] thread_local link error

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59364

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
      Known to work|                            |4.9.0
         Resolution|---                         |FIXED

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Works in 4.9.

[Bug c++/59364] thread_local link error

[conradsand.arma at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59364

--- Comment #6 from Conrad <conradsand.arma at gmail dot com> ---
Any chance of a backport of this fix to gcc 4.8.3 ?

[Bug c++/59364] thread_local link error

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59364

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I thought I've commented on this, perhaps in other PR, but can't find it right
now.  The link error disappeared with r199577, which certainly doesn't seem to
be backportable nor a change with the intent to fix this, and furthermore, I'd
say that for such a trivial (sure, not in C++ terminology) ctor we'd better not
to require dynamic initialization of the TLS var.

[Bug c++/59364] thread_local link error

[jason at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59364

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org
         Resolution|FIXED                       |DUPLICATE

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
Duplicate, yes.

*** This bug has been marked as a duplicate of bug 55800 ***