Re: [PATCH] detect incompatible aliases (PR c/81854)

[Martin Sebor <msebor at gmail dot com>]

On 08/18/2017 07:10 AM, Jonathan Wakely wrote:
> On 17/08/17 21:21 -0600, Martin Sebor wrote:
> > Joseph, while looking into implementing enhancement your request
> > pr81824 I noticed that GCC silently accepts incompatible alias
> > declarations (pr81854) so as sort of a proof-concept for the
> > former I enhanced the checking already done for other kinds of
> > incompatibilities to also detect those mentioned in the latter
> > bug.  Attached is this patch, tested on x85_64-linux.
> >
> > Jonathan, the patch requires suppressing the warning in libstdc++
> > compatibility symbol definitions in compatibility.cc.  I couldn't
> > find a way to do it without the suppression but I'd be happy to
> > try again if you have an idea for how.
>
> Doing it that way is fine, but ...
>
> > diff --git a/libstdc++-v3/src/c++98/compatibility.cc
> > b/libstdc++-v3/src/c++98/compatibility.cc
> > index 381f4c4..5f56b9e 100644
> > --- a/libstdc++-v3/src/c++98/compatibility.cc
> > +++ b/libstdc++-v3/src/c++98/compatibility.cc
> > @@ -213,6 +213,11 @@ _ZNSt19istreambuf_iteratorIcSt11char_traitsIcEEppEv
> > _ZNSt19istreambuf_iteratorIwSt11char_traitsIwEEppEv
> >  */
> >
> > +// Disable warning about declaring aliases between functions with
> > +// incompatible types.
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Wattributes"
> > +
>
> Could this be moved closer to the point where it's needed?
>
> It's not needed until after line 361, right?

Sure.  The other possibility that I forgot to mention is to
declare the alias without a prototype, which in C++ looks
like this:

  void foo (...);

The patch would then look like this.  Do you have a preference
between these two approaches?

Martin

diff --git a/libstdc++-v3/src/c++98/compatibility.cc 
b/libstdc++-v3/src/c++98/compatibility.cc
index 381f4c4..b49a5ca 100644
--- a/libstdc++-v3/src/c++98/compatibility.cc
+++ b/libstdc++-v3/src/c++98/compatibility.cc
@@ -367,13 +367,13 @@ _GLIBCXX_END_NAMESPACE_VERSION

 #define _GLIBCXX_3_4_SYMVER(XXname, name) \
    extern "C" void \
-   _X##name() \
+   _X##name(...) \
    __attribute__ ((alias(#XXname))); \
    asm (".symver " "_X" #name "," #name "@GLIBCXX_3.4");

 #define _GLIBCXX_3_4_5_SYMVER(XXname, name) \
    extern "C" void \
-   _Y##name() \
+   _Y##name(...) \
    __attribute__ ((alias(#XXname))); \
    asm (".symver " "_Y" #name  "," #name "@@GLIBCXX_3.4.5");