[libstdc++ 3.0] alternative 3.0-branch patch for PR 3720

[Joe Buck <jbuck at synopsys dot COM>]

I foolishly wrote:
> > In any case, I'll get you something today.

Mark:
> Thanks!

This is the one where the following program crashes:

#include <iostream>
int main() {
	int i;
	std::cin >> i;
}

if the user just types a whole lot of digits.

OK, here's the problem.  Backporting Ben's patch would break the ABI.  This
begs the question, is there something else we can do?

In any case, what I notice is that in locale_facets.tcc, every single
call to _M_extract passes a 32-char array as the argument that accumulates
characters.  There are no other calls to this _M_extract.  So, why not
move the limit down into _M_extract?

Here is my suggested extremely bad hack.  Before anyone objects to the
magic number "31", take a look at locale_facets.tcc and all the uses of
"32".  Don't we have a rule about such things?

At least in the case of cin >> intvar it blocks the crash.  However, I
freely admit that it is a kludge.  All I can say in its defense is that
I can promise that it doesn't change the ABI, and it even improves
things for programs already built with 3.0 through 3.0.2 (if the
new libstdc++ is installed).

The other advantage of this patch is that you can accept it without
papers, because of its small size: 5 code lines, two of which contain
only a curly.

My standard at this late date is
1) is it safe?
2) does it make things better?

so I think that this makes it, even if it's far from perfect.
So, without further ado:

------------------------------------------------------------------
2001-12-10  Joe Buck <jbuck@synopsys.com>
	PR libstdc++/3720 (different from fix on trunk, to preserve the ABI)
        * src/locale.cc (_M_extract): Avoid buffer overrun.

Index: locale.cc
===================================================================
RCS file: /cvs/gcc/egcs/libstdc++-v3/src/locale.cc,v
retrieving revision 1.28.2.4
diff -c -r1.28.2.4 locale.cc
*** locale.cc	2001/07/20 00:14:10	1.28.2.4
--- locale.cc	2001/12/11 00:27:20
***************
*** 774,779 ****
--- 774,791 ----
        bool __testunits = __testzero;
        while (__beg != __end)
          {
+ 
+ 	  // very bad hack: __xtrc is always a 32-char array, and nothing
+ 	  // checks for overruns.  Do it this way to fail if someone types
+ 	  // 32 or more digits.  This is a temporary fix to avoid breaking
+ 	  // the 3.0.x library ABI.  The stream may not be left in the
+ 	  // right position, but at least we don't crash.
+ 	  if (__pos >= 31)
+ 	    {
+ 	      __err |= ios_base::failbit;
+ 	      return;
+ 	    }
+ 
            const char* __p = strchr(__lits, __c);
  
            // NB: strchr returns true for __c == 0x0