standards/175453: Catching C++ std::bad_cast doesn't work in FreeBSD 9.1

[Pedro Giffuni]

----- Messaggio originale -----
> Da: Konstantin Belousov 
> 
> On Sun, Jan 20, 2013 at 04:52:00PM +0000, Hongli Lai wrote:
>> 
>>  >Number:         175453
>>  >Category:       standards
>>  >Synopsis:       Catching C++ std::bad_cast doesn't work in FreeBSD 
> 9.1
>>  >Confidential:   no
>>  >Severity:       non-critical
>>  >Priority:       low
>>  >Responsible:    freebsd-standards
>>  >State:          open
>>  >Quarter:        
>>  >Keywords:      
>>  >Date-Required:
>>  >Class:          sw-bug
>>  >Submitter-Id:   current-users
>>  >Arrival-Date:   Sun Jan 20 17:00:00 UTC 2013
>>  >Closed-Date:
>>  >Last-Modified:
>>  >Originator:     Hongli Lai
>>  >Release:        9.1-RELEASE
>>  >Organization:
>>  Phusion
>>  >Environment:
>>  FreeBSD freebsd9 9.1-RELEASE FreeBSD 9.1-RELEASE #0 r243825: Tue Dec  4 
> 09:23:10 UTC 2012    
>>  root at farrell.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  amd64
>>  >Description:
>>  C++ code is not able to catch std::bad_cast exceptions, even though it 
> should. If a dynamic_cast is within a try-catch block, then that block fails to 
> catch std::bad_cast, and the program crashes with an uncaught exception as a 
> result.
>> 
>>  I've attached a reproducible test case. You can also find it at 
> http://forums.freebsd.org/showthread.php?p=205804#post205804 and 
> http://stackoverflow.com/questions/14413703/why-does-catching-stdbad-cast-not-work-on-freebsd-9. 
> The code is compiled with the following GCC version:
>> 
>>  $ gcc -v
>>  Using built-in specs.
>>  Target: amd64-undermydesk-freebsd
>>  Configured with: FreeBSD/amd64 system compiler
>>  Thread model: posix
>>  gcc version 4.2.1 20070831 patched [FreeBSD]
>> 
>>  FreeBSD 9.1 seems to be the only platform on which this bug appears. The 
> code works as expected on Linux and OS X. According to a commenter, FreeBSD 9.0 
> works as expected too. According to another commenter the code fails on FreeBSD 
> 9.1 with Clang too.
>>  >How-To-Repeat:
>>  See attached C++ program.
>>  >Fix:
>> 
>> 
>>  Patch attached with submission follows:
>> 
>>  #include <exception>
>>  #include <typeinfo>
>>  #include <stdio.h>
>> 
>>  class foo {
>>  public:
>>      virtual ~foo() {}
>>  };
>> 
>>  class bar: public foo {
>>  public:
>>      int val;
>>      bar(): val(123) {}
>>  };
>> 
>>  static void
>>  cast_test(const foo &f) {
>>      try {
>>          const bar &b = dynamic_cast<const bar &>(f);
>>          printf("%d\n", b.val);
>>      } catch (const std::bad_cast &) {
>>          printf("bad cast\n");
>>      }
>>  }
>> 
>>  int main() {
>>      foo f;
>>      cast_test(f);
>>      return 0;
>>  }
>> 
> Confirmed, and it seems that the culprit is libstdc++. At least replacing
> the system libstdc++.so.6 with the library from the stock build of gcc
> 4.7.2 (without touching libgcc_s.so.1) makes the catch operator working.
> 

Confirmed,
 
The problem is actually not in any of the code updates to libstdc++ but
in the way libstdc++ is configured/build since 9.0.

Reverting the changes in stable/9/gnu/lib/libstdc up to r229037 things work
just fine.

I suspect the culprit is r233749 and subsequent changes to build libstdc++
as a filter library for libsupc++.

This also seems similar ot PR kern/171610.

Pedro.