Re: PR libstdc++/60587

[Jonathan Wakely <jwakely at redhat dot com>]

On 19/03/14 23:38 +0100, Paolo Carlini wrote:
> > > On 19/03/14 21:39 +0000, Jonathan Wakely wrote:
> > > I think the safe thing to do is (as I suggested at the time) to have a
> > > trait saying which iterator types refer to contiguous memory. Our
> > > debug mode only supports our own containers, so the ones which are
> > > contiguous are known.  For 4.9.0 I think the right option is simply
> > > to remove __foreign_iterator_aux3 and __foreign_iterator_aux4
> > > completely. The fixed version of __foreign_iterator_aux2() can detect
> > > when we have iterators referring to the same sequence, which is what
> > > we really want to detect. That's what the attached patch does and what
> > > I'm going to test.
> >
> > With my suggested change we get an XPASS for
> > testsuite/23_containers/vector/debug/57779_neg.cc
> >
> > An __is_contiguous trait would solve that.
>
> Funny, I thought we already had it...

I think we might have added it and removed it at some point ... not
sure though.

This is what I plan to commit, it's almost a total rewrite of
__foreign_iterator()  :-(

Dereferencing invalid iterators is avoided by passing in both
iterators representing the range, not just the first.

The suspect pointer arithmetic that tries to determine if a pointer
points inside a container is made unnecessary by adding
__gnu_debug::_Is_contiguous_sequence, currently only true for
std::vector<T,A> for all T except bool.  We don't need to make it true
for std::string because that defines _Insert_range_from_self_is_safe
instead, so we can never reach the code that depends on contiguous
storage. As a benefit of the rewrite it no longer depends on C++11 and
so works in C++98 mode.

The overload resolution issue is solved by consistently using
const-refs for the parameters of __foreign_iterator_aux2. I also added
another overload for debug iterators into different debug container
types, so they can be identified as foreign sooner, without calling
__foreign_iterator_aux3.

Everything passes for "make check check-debug", so I plan to commit it
tomorrow, unless anyone points out a problem.

Attachment: patch.txt
Description: Text document