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From: "junchao.zhang at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/107535] New: Shouldn't -fvisibility=hidden hide C++17
 inline static variables?
Date: Sat, 05 Nov 2022 12:38:34 +0000
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X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 11.3.1
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: junchao.zhang at gmail dot com
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107535

            Bug ID: 107535
           Summary: Shouldn't -fvisibility=3Dhidden hide C++17 inline static
                    variables?
           Product: gcc
           Version: 11.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: junchao.zhang at gmail dot com
  Target Milestone: ---

I think inline static variables are global. However, they could be hidden by
-fvisibility=3Dhidden.
This is dangerous, since with C++17 inline static variables,  they will app=
ear
in headers and be included in *.cpp files. If the *.cpp files are compiled =
with
-fvisibility=3Dhidden, each will get their own storage.

$ cat foo.hpp=20
struct Foo {static inline int s =3D 100; };
extern __attribute__ ((visibility ("default"))) void DumpLibFoo();

$ cat foo.cpp
#include <stdio.h>
#include <foo.hpp>
void DumpLibFoo() { printf("In libfoo, Foo::s (%p) =3D %d\n", &Foo::s, Foo:=
:s); }

$ cat test.cpp
#include <stdio.h>
#include <foo.hpp>

int main() {
  Foo::s =3D 200;
  printf("In main,   Foo::s (%p) =3D %d\n", &Foo::s, Foo::s);

  DumpLibFoo();
  return 0;
}

-----
gcc -std=3Dc++17 -c -fPIC -I./ test.cpp -fvisibility=3Dhidden
gcc -std=3Dc++17 -c -fPIC -I./ foo.cpp
gcc -o libfoo.so -shared foo.o
gcc -std=3Dc++17 -o test test.o -Wl,-rpath ./ -L ./ -lfoo

./test
In main,   Foo::s (0x5604c2741010) =3D 200
In libfoo, Foo::s (0x7f4e5173d028) =3D 100=