From: Jonathan Wakely <jwakely@redhat.com>
To: "François Dumont" <frs.dumont@gmail.com>
Cc: libstdc++ <libstdc++@gcc.gnu.org>, gcc-patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Fix -Wstringop-overflow warning in 23_containers/vector/types/1.cc
Date: Tue, 28 May 2024 11:28:27 +0100 [thread overview]
Message-ID: <ZlWxyz0zhtd3KfCc@zen.kayari.org> (raw)
In-Reply-To: <4657346e-3046-424a-be1d-32a7eaecae32@gmail.com>
On 27/05/24 22:07 +0200, François Dumont wrote:
>In C++98 this test fails with:
>
>Excess errors:
>/home/fdumont/dev/gcc/build/x86_64-pc-linux-gnu/libstdc++-v3/include/bits/stl_algobase.h:452:
>warning: 'void* __builtin_memcpy(void*, const void*, long unsigned
>int)' writing between 2 and 9223372036854775806 bytes into a region of
>size 0 overflows the destination [-Wstringop-overflow=]
>
>The attached patch avoids this warning.
>
> libstdc++: Fix -Wstringop-overflow warning coming from std::vector
>
> Make vector<>::_M_range_insert implementation more transparent to
>the compiler checks.
>
> Extend local copies of members to the whole method scope so that
>all branches benefit
> from those.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/vector.tcc
> (std::vector<>::_M_range_insert(iterator, _FwdIt, _FwdIt,
>forward_iterator_tag)):
> Use local copies of members to call the different algorithms.
>
>Ok to commit if all tests passes ?
>
>François
>diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc
>index 36b27dce7b9..671929dee55 100644
>--- a/libstdc++-v3/include/bits/vector.tcc
>+++ b/libstdc++-v3/include/bits/vector.tcc
>@@ -885,83 +885,80 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
> {
> if (__first != __last)
> {
>+ // Make local copies of these members because the compiler
>+ // thinks the allocator can alter them if 'this' is globally
>+ // reachable.
>+ pointer __start = this->_M_impl._M_start;
>+ pointer __end = this->_M_impl._M_end_of_storage;
>+ pointer __finish = this->_M_impl._M_finish;
>+ pointer __pos = __position.base();
>+ _Tp_alloc_type& __allocator = _M_get_Tp_allocator();
>+
>+ if (__pos < __start || __finish < __pos)
>+ __builtin_unreachable();
I don't think we should use __builtin_unreachable for something which
is not an invariant of the class. The __position argument is supplied
by the user, so we should not make promises about it being valid,
because we can't know that.
We can promise that __start <= __finish, and that __finish <= end,
because we control those. We can't promise the user won't pass in a
bad __position. Although it's undefined for the user to do that, using
__builtin_unreachable() here makes the effects worse, and makes it
harder to debug.
Also, (__pos < __start) might already trigger undefined behaviour for
fancy pointers, if they don't point to the same memory region.
So this change is not OK.
>+
> const size_type __n = std::distance(__first, __last);
>- if (size_type(this->_M_impl._M_end_of_storage
>- - this->_M_impl._M_finish) >= __n)
>+ if (size_type(__end - __finish) >= __n)
> {
>- const size_type __elems_after = end() - __position;
>- pointer __old_finish(this->_M_impl._M_finish);
>+ const size_type __elems_after = __end - __pos;
>+ pointer __old_finish(__finish);
> if (__elems_after > __n)
> {
> _GLIBCXX_ASAN_ANNOTATE_GROW(__n);
>- std::__uninitialized_move_a(this->_M_impl._M_finish - __n,
>- this->_M_impl._M_finish,
>- this->_M_impl._M_finish,
>- _M_get_Tp_allocator());
>- this->_M_impl._M_finish += __n;
>+ __finish = std::__uninitialized_move_a
>+ (__finish - __n, __finish, __finish, __allocator);
> _GLIBCXX_ASAN_ANNOTATE_GREW(__n);
>- _GLIBCXX_MOVE_BACKWARD3(__position.base(),
>- __old_finish - __n, __old_finish);
>- std::copy(__first, __last, __position);
>+ _GLIBCXX_MOVE_BACKWARD3
>+ (__pos, __old_finish - __n, __old_finish);
>+ std::copy(__first, __last, __pos);
> }
> else
> {
> _ForwardIterator __mid = __first;
> std::advance(__mid, __elems_after);
> _GLIBCXX_ASAN_ANNOTATE_GROW(__n);
>- std::__uninitialized_copy_a(__mid, __last,
>- this->_M_impl._M_finish,
>- _M_get_Tp_allocator());
>- this->_M_impl._M_finish += __n - __elems_after;
>+ __finish = std::__uninitialized_copy_a
>+ (__mid, __last, __finish, __allocator);
> _GLIBCXX_ASAN_ANNOTATE_GREW(__n - __elems_after);
>- std::__uninitialized_move_a(__position.base(),
>- __old_finish,
>- this->_M_impl._M_finish,
>- _M_get_Tp_allocator());
>- this->_M_impl._M_finish += __elems_after;
>+ __finish = std::__uninitialized_move_a
>+ (__pos, __old_finish, __finish, __allocator);
> _GLIBCXX_ASAN_ANNOTATE_GREW(__elems_after);
>- std::copy(__first, __mid, __position);
>+ std::copy(__first, __mid, __pos);
> }
>+
>+ this->_M_impl._M_finish = __finish;
> }
> else
> {
>- // Make local copies of these members because the compiler
>- // thinks the allocator can alter them if 'this' is globally
>- // reachable.
>- pointer __old_start = this->_M_impl._M_start;
>- pointer __old_finish = this->_M_impl._M_finish;
>-
>+ const size_type __size = size_type(__finish - __start);
> const size_type __len =
> _M_check_len(__n, "vector::_M_range_insert");
>+ if (__len < __n + __size)
>+ __builtin_unreachable();
>+
> pointer __new_start(this->_M_allocate(__len));
> pointer __new_finish(__new_start);
> __try
> {
> __new_finish
> = std::__uninitialized_move_if_noexcept_a
>- (__old_start, __position.base(),
>- __new_start, _M_get_Tp_allocator());
>+ (__start, __pos, __new_start, __allocator);
> __new_finish
>- = std::__uninitialized_copy_a(__first, __last,
>- __new_finish,
>- _M_get_Tp_allocator());
>+ = std::__uninitialized_copy_a
>+ (__first, __last, __new_finish, __allocator);
> __new_finish
> = std::__uninitialized_move_if_noexcept_a
>- (__position.base(), __old_finish,
>- __new_finish, _M_get_Tp_allocator());
>+ (__pos, __finish, __new_finish, __allocator);
> }
> __catch(...)
> {
>- std::_Destroy(__new_start, __new_finish,
>- _M_get_Tp_allocator());
>+ std::_Destroy(__new_start, __new_finish, __allocator);
> _M_deallocate(__new_start, __len);
> __throw_exception_again;
> }
>- std::_Destroy(__old_start, __old_finish,
>- _M_get_Tp_allocator());
>+ std::_Destroy(__start, __finish, __allocator);
> _GLIBCXX_ASAN_ANNOTATE_REINIT;
>- _M_deallocate(__old_start,
>- this->_M_impl._M_end_of_storage - __old_start);
>+ _M_deallocate(__start, __end - __start);
> this->_M_impl._M_start = __new_start;
> this->_M_impl._M_finish = __new_finish;
> this->_M_impl._M_end_of_storage = __new_start + __len;
next prev parent reply other threads:[~2024-05-28 10:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-27 20:07 François Dumont
2024-05-27 20:18 ` Sam James
2024-05-27 20:58 ` François Dumont
2024-05-28 10:28 ` Jonathan Wakely [this message]
2024-05-30 5:11 ` François Dumont
2024-05-30 11:07 ` Jonathan Wakely
2024-06-03 4:56 ` [PATCH] Fix -Wstringop-overflow warning in 23_containers/vector/types/1.cc PR109849 François Dumont
2024-06-03 16:20 ` Jonathan Wakely
2024-06-03 17:46 ` François Dumont
2024-06-03 19:08 ` Jonathan Wakely
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