[Bug c++/55148] New: wrong compilation of chars: overlapped memory areas

[Bug c++/55148] New: wrong compilation of chars: overlapped memory areas

[icegood1980 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55148

             Bug #: 55148
           Summary: wrong compilation of chars: overlapped memory areas
    Classification: Unclassified
           Product: gcc
           Version: 4.7.2
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: icegood1980@gmail.com


if one uses a stringification operation then problems could be obtained on
stack:

brackets.cpp : 

#include <iostream>
#include <cstring>
#define GLOBAL_str_intermediate(s)                                            \
({                                                                            \
  char GLOBAL_str_intermediate_buf[1024];                                     \
  strcpy(GLOBAL_str_intermediate_buf, #s);                                    \
  GLOBAL_str_intermediate_buf[strlen(GLOBAL_str_intermediate_buf)-1]='\0';    \
  GLOBAL_str_intermediate_buf+1;                                              \
})

#define GLOBAL_str(s) GLOBAL_str_intermediate((s))
#define s_one_arg a,b,c

int main(int argc, const char **argv)
{
  char PairPotentialName[70], *p=GLOBAL_str(s_one_arg);
  //
  std::cerr<<p-PairPotentialName<<std::endl;
  std::cerr<<PairPotentialName+1<<std::endl;
  return 0;
}

g++ brackets.cpp 
./a.out:
1
a,b,c
so PairPotentialName and p are overlapped!

[Bug c++/55148] wrong compilation of chars: overlapped memory areas

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55148

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|major                       |normal

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-10-31 12:16:51 UTC ---
As the docs for the Statement Expressions extension
(http://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html) say:

"Any temporaries created within a statement within a statement expression will
be destroyed at the statement's end."

so GLOBAL_str_intermediate_buf[] is no longer valid after p is initialized and
the memory can be reused.

[Bug c++/55148] wrong compilation of chars: overlapped memory areas

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55148

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-10-31 12:22:54 UTC ---
http://gcc.gnu.org/gcc-4.7/changes.html#cxx notes "G++ now properly re-uses
stack space allocated for temporary objects when their lifetime ends, which can
significantly lower stack consumption for some C++ functions. As a result of
this, some code with undefined behavior will now break"

[Bug c++/55148] wrong compilation of chars: overlapped memory areas

[icegood1980 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55148

icegood1980@gmail.com <icegood1980 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |major

--- Comment #3 from icegood1980 at gmail dot com <icegood1980 at gmail dot com> 2012-10-31 12:40:16 UTC ---
Clear! it's my fault.

[Bug c++/55148] wrong compilation of chars: overlapped memory areas

[icegood1980 at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55148

icegood1980@gmail.com <icegood1980 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #4 from icegood1980 at gmail dot com <icegood1980 at gmail dot com> 2012-10-31 12:43:32 UTC ---
my fault