| Summary: | thread_local link error | ||
|---|---|---|---|
| Product: | gcc | Reporter: | Conrad S <conradsand.arma> |
| Component: | c++ | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | major | CC: | daniel.kruegler, hubicka, jakub, jakub, jason, jason, oleg, victor.dyachenko |
| Priority: | P3 | ||
| Version: | 4.8.2 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Known to work: | 4.9.0 | |
| Known to fail: | 4.8.2 | Last reconfirmed: | |
| Bug Depends on: | |||
| Bug Blocks: | 59994 | ||
| Attachments: | reduced test case | ||
This seems to be a duplicate of bug #55800. The workaround mentioned in the comments fixes the problem. 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. Reduced test case. Compile with:
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
file foo.hpp:
class foo
{
public:
inline foo() {}
inline ~foo() {}
inline double bar() { return 123.456; }
};
file a.cpp:
#include "foo.hpp"
thread_local foo foo_instance;
file b.cpp:
#include "foo.hpp"
extern thread_local foo foo_instance;
int main(int argc, char** argv)
{
double bar = foo_instance.bar();
return 0;
}
Created attachment 31406 [details]
reduced test case
Attached reduced_test_case.tar.gz
No need for pre-processed input, as it doesn't include any system headers.
Works in 4.9. Any chance of a backport of this fix to gcc 4.8.3 ? 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. |
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; } ---