[cfe-dev] Inline function static variable linkage visibility issue

[Rick Taylor]

Hi All,

I have found an inconsistency between gcc and clang's handling of the linkage of static variables in visibility(hidden) member functions, when linked as shared objects.

A quick worked example:

/////////////////////////////////
/////// foo.cpp
class Foo
{
public:
	static const int* Bar()
	{
		const static int _bar[] = { 1,2,3,4 };
		return _bar;
	}
};

void __attribute__((visibility("default"))) external_fn()
{
	const int* i = Foo::Bar();
}

//////////////////////////////////////


And the output from nm:

$ clang++ -fvisibility=hidden -c foo.cpp
$ clang++ -shared -fvisibility=hidden foo.o -o foo
$ nm -D -C foo
         w _Jv_RegisterClasses
00000480 T external_fn()
00000504 V Foo::Bar()::_bar       <-- THIS IS THE PROBLEM
0000200c A __bss_start
         w __cxa_finalize
         w __gmon_start__
0000200c A _edata
00002014 A _end
000004e8 T _fini
00000358 T _init

$ g++ -fvisibility=hidden -c foo.cpp
$ g++ -shared -fvisibility=hidden foo.o -o foo.g
$ nm -D -C foo.g
         w _Jv_RegisterClasses
0000049c T external_fn()
0000200c A __bss_start
         w __cxa_finalize
         w __gmon_start__
         U __gxx_personality_v0
0000200c A _edata
00002014 A _end
000004f8 T _fini
00000380 T _init

Now I am not sure which is correct (I know there is some complex logic involved in inline member function static variables) but I am relying on the gcc linkage for the plugin layer of my project.

I have tried library sprinkling my code with __attribute__((visibility("hidden"))) on each of the static variable declarations, but that appears to make no difference, and is not required by gcc either.

Can someone more familiar with the clang codebase confirm this as a bug or my stupidity please?

Many thanks

Rick Taylor