stack overflow bug in ofstream::operator<<

Igor Pechtchanski
Tue Jun 28 17:12:00 GMT 2005

On Tue, 28 Jun 2005, Dave Korn wrote:

> ----Original Message----
> >From: Corinna Vinschen
> >Sent: 28 June 2005 16:57
> > I had something like that as a local patch but that's a bit dangerous.
>   Well, yeh.  But somewhat less dangerous than the existing situation!
> > Imagine a process using lots of stack space before calling writev and
> > there's only, say, 32K left.
>   Imagine a process using no stack space at all before calling writev and
> there's only, say, 2Mb left.  Oh, hang on, that's where we came in!
> > It would potentially get a SEGV since
> > alloca is used while it would still work when using malloc.  Of course
> > malloc could fail for a process using lots of malloc'ed space.  However,
> > malloc should at least not SEGV but just return with a NULL pointer...
>   Indeed, and perhaps the best fix of all would be if alloca was able to
> return NULL when there wasn't enough space on the stack.
> > So, I guess I'll just check it in using malloc.
>   Hmm.  Can't we tell how much space there is on the stack from the pointers
> to the stack limits in the NT_TIB (or whatever lives at %fs on 9x), where we
> get the tls pointers from?

I wonder -- would temporarily installing a signal handler be too much
overhead?  Or is it a thread safety issue (global vars, etc)?
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