Re: Lua 5.1wk6 visibility("hidden") attribute in luaconf.h

[Kein-Hong Man <mkh@...>]

Hi all,

Mike Pall wrote:
> Kein-Hong Man wrote:
> > On Mingw (gcc version 3.2.3 (mingw special 20030504-1)):
> > lundump.h:14: warning: `visibility' attribute directive ignored
> > lundump.h:17: warning: `visibility' attribute directive ignored
> > [...]
> > On Cygwin (gcc version 3.3.3 (cygwin special)):
> > lundump.c:288: warning: visibility attribute not supported in this 
> > configuration; ignored
>
> It seems gcc warns about the visibility attribute when the
> target format (in this case WIN32 executable images) does not
> support it, even though the compiler recognizes the attribute.
>
> > The URL http://www.ohse.de/uwe/articles/gcc-attributes.html
> > claims 'visibility' is found in >=3.3, so I wonder if someone can 
> > confirm whether ((__GNUC__*100 + __GNUC_MINOR__) >= 302) should be 
> > 303 instead in luaconf.h. Does anyone have advice on what to do 
> > with the Cygwin warning messages?

Thanks, the fix below works. To answer my own question (above), 
302 is correct; gcc 3.2.2 on RH9 compiles without warnings. I was 
misled by these two particular Mingw and Cygwin gcc versions 
having slightly different warning messages.

> The main point was that the compiler produces better code for calls
> to functions with hidden visibility inside PIC shared libraries.
> This is not relevant for Windows (DLLs do not contain PIC) and can
> be disabled there.
>
> So one probably needs to modify luaconf.h line 127 to include only
> ELF targets (but I'm not sure if __ELF__ is defined everywhere):
>
> #elif defined(__GNUC__) && ((__GNUC__*100 + __GNUC_MINOR__) >= 302) && \
>       defined(__ELF__)
>
> ... or to explicitly exclude the WIN32 gcc ports (since _WIN32 is
> not defined for Cygwin):
>
> #elif defined(__GNUC__) && ((__GNUC__*100 + __GNUC_MINOR__) >= 302) && \
>       !defined(__CYGWIN__) && !defined(__MINGW32__)
> [snip]

I'm not sure which is better. There might be other gcc targets 
that are non-ELF. gcc documentation on attributes mentions cygwin, 
mingw and arm-pe.

--
Cheers,
Kein-Hong Man (esq.)
Kuala Lumpur, Malaysia