Given the following code:
===
struct EditorInternalCommand { };
static void createCommandMap()
{
struct CommandEntry { EditorInternalCommand command; };
}
===
The structure createCommandMap()::CommandEntry is exported from a local-scope
(static) function. When compiling the code above with -fvisibility=hidden, g++
4.3 or 4.4 outputs the following warning:
visibility.cpp:5: warning: 'createCommandMap()::CommandEntry' declared with
greater visibility than the type of its field
'createCommandMap()::CommandEntry::command'
If I add constructors to both structures so that there are symbols emitted, the
ELF symbol table looks like this:
6: 00000000 22 FUNC LOCAL DEFAULT 2
_ZZL16createCommandMapvEN12CommandEntryC1Ev
7: 00000016 16 FUNC LOCAL DEFAULT 2 _ZL16createCommandMapv
12: 00000000 5 FUNC WEAK HIDDEN 6
_ZN21EditorInternalCommandC1Ev
My understanding of the problem is that a "static" function has LOCAL scope but
DEFAULT visibility. The inner structure inherits these properties. However, the
outer structure (EditorInternalCommand) has HIDDEN visibility, which triggers
the warning.
However, since the binding scope is LOCAL, those symbols will not be exported
by the linker in the final ELF object anyways, thereby making them effectively
have hidden visibility.
Workarounds:
Any of the following three actions make the warning disappear:
1) remove the "static" keyword
2) move the inner structure outside the static function
3) place the outer structure in an anonymous namespace
Actions #2 and #3 above change those propeties making both constructors match
either LOCAL/DEFAULT or WEAK/HIDDEN. Action #1 causes the function to become
GLOBAL/HIDDEN, but leaves the inner structure unchanged -- however, the warning
is gone too.
--
Summary: structure inside a static function is exported,
producing warning
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: thiago at kde dot org
GCC build triplet: i586-manbo-linux-gnu
GCC host triplet: i586-manbo-linux-gnu
GCC target triplet: i586-manbo-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40145
