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

[Jonathan Wakely]

On 18/08/17 08:54 -0600, Martin Sebor wrote:
>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?

If this doesn't change the generated code, but avoids the warnings
then I think I prefer this. i.e. fix the code, not just suppress the
warnings.


>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");
>
>