https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69125
Bug ID: 69125
Summary: [6 regression] Please don't print "‘visibility’
attribute ignored" when setting hidden visibility for
anonymous namespace classes
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: thiago at kde dot org
Target Milestone: ---
The following code compiled without warnings in GCC < 6 and now prints a
warning:
$ cat /tmp/test.cpp
#define Q_OBJECT \
__attribute__((visibility("hidden"))) static void qt_static_metacall();
namespace {
class A
{
Q_OBJECT
};
}
$ ~/gcc6/bin/gcc -O2 -c /tmp/test.cpp
/tmp/test.cpp:2:74: warning: ‘visibility’ attribute ignored [-Wattributes]
__attribute__((visibility("hidden"))) static void qt_static_metacall();
^
/tmp/test.cpp:7:5: note: in expansion of macro ‘Q_OBJECT’
Q_OBJECT
^~~~~~~~
IIUC, classes in anonymous namespaces are getting internal linkage, which means
the visibility attribute is superfluous.
But the Q_OBJECT macro needs to have that __attribute__. We would rather not
pessimise all public classes to suppress this warning.
Alternatively, please provide a way to suppress the warning in the macro. I
tried using _Pragma but the warning remains:
#define Q_OBJECT \
_Pragma("GCC diagnostic ignored \"-Wattributes\"") \
__attribute__((visibility("hidden"))) static void qt_static_metacall();
Note that with this definition, the preprocessed source does not produce the
warning:
$ ~/gcc6/bin/gcc -E /tmp/test.cpp | ~/gcc6/bin/gcc -O0 -c -xc++ -
