libstdc++: [_GLIBCXX_DEBUG] Fix std::__niter_wrap behavior
In _GLIBCXX_DEBUG mode the std::__niter_base can remove 2 layers, the
__gnu_debug::_Safe_iterator<> and the __gnu_cxx::__normal_iterator<>.
When std::__niter_wrap is called to build a
__gnu_debug::_Safe_iterator<>
from a __gnu_cxx::__normal_iterator<> we then have a consistency issue
as the difference between the 2 iterators will done on a
__normal_iterator
on one side and a C pointer on the other. To avoid this problem call
std::__niter_base on both input iterators.
libstdc++-v3/ChangeLog:
* include/bits/stl_algobase.h (std::__niter_wrap): Add a
call to
std::__niter_base on res iterator.
Tested under Linux x86_64 normal and _GLIBCXX_DEBUG modes in c++98,
c++11, c++17.
Ok to commit ?
François
On 19/02/2024 09:21, Jonathan Wakely wrote:
On Mon, 19 Feb 2024, 08:12 Jonathan Wakely, <jwakely....@gmail.com> wrote:
On Mon, 19 Feb 2024, 07:08 Stephan Bergmann, <sberg....@gmail.com>
wrote:
On 2/17/24 15:14, François Dumont wrote:
> Thanks for the link, tested and committed.
I assume this is the cause for the below failure now,
Yes, the new >= C++11 overload of __niter_base recursively unwraps
multiple layers of wrapping, so that a safe iterator wrapping a
normal iterator wrapping a pointer is unwrapped to just a pointer.
But then __niter_wrap doesn't restore both layers.
Actually that's not the problem. __niter_wrap would restore both
layers, except that it uses __niter_base itself:
> 347 | { return __from + (__res - std::__niter_base(__from)); }
> | ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
And it seems to be getting called with the wrong types. Maybe that's
just a bug in std:: erase or maybe niter_wrap needs adjusting.
I'll check in a couple of hours if François doesn't get to it first.
I have to wonder how this wasn't caught by existing tests though.
diff --git a/libstdc++-v3/include/bits/stl_algobase.h
b/libstdc++-v3/include/bits/stl_algobase.h
index 0f73da13172..d534e02871f 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -344,7 +344,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_GLIBCXX20_CONSTEXPR
inline _From
__niter_wrap(_From __from, _To __res)
- { return __from + (__res - std::__niter_base(__from)); }
+ { return __from + (std::__niter_base(__res) - std::__niter_base(__from)); }
// No need to wrap, iterator already has the right type.
template<typename _Iterator>
