From 4366711d2d66ea9a2d4fe9dd112795ef0c6f785c Mon Sep 17 00:00:00 2001 From: Jonathan Wakely Date: Fri, 28 Mar 2025 22:00:38 +0000 Subject: [PATCH] libstdc++: Fix bogus -Wstringop-overflow in std::vector::insert [PR117983] MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit This was fixed on trunk by r15-4473-g3abe751ea86e34, but that isn't suitable for backporting. Instead, just add another unreachable condition in std::vector::_M_range_insert so the compiler knows this memcpy doesn't use a length originating from a negative ptrdiff_t converted to a very positive size_t. libstdc++-v3/ChangeLog: PR libstdc++/117983 * include/bits/vector.tcc (vector::_M_range_insert): Add unreachable condition to tell the compiler begin() <= end(). * testsuite/23_containers/vector/modifiers/insert/117983.cc: New test. Reviewed-by: Tomasz Kamiński (cherry picked from commit 878812b6f6905774ab37cb78903e3e11bf1c508c) --- libstdc++-v3/include/bits/vector.tcc | 2 ++ .../vector/modifiers/insert/117983.cc | 17 +++++++++++++++++ 2 files changed, 19 insertions(+) create mode 100644 libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/117983.cc diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc index 0bd1ae41102..200a75a19c3 100644 --- a/libstdc++-v3/include/bits/vector.tcc +++ b/libstdc++-v3/include/bits/vector.tcc @@ -1005,6 +1005,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER // reachable. pointer __old_start = this->_M_impl._M_start; pointer __old_finish = this->_M_impl._M_finish; + if ((__old_finish - __old_start) < 0) + __builtin_unreachable(); const size_type __len = _M_check_len(__n, "vector::_M_range_insert"); diff --git a/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/117983.cc b/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/117983.cc new file mode 100644 index 00000000000..e6027a677ee --- /dev/null +++ b/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/117983.cc @@ -0,0 +1,17 @@ +// { dg-options "-O3 -Werror=stringop-overflow" } +// { dg-do compile } + +// PR libstdc++/117983 +// -Wstringop-overflow false positive for __builtin_memmove from vector::insert + +#include + +typedef std::vector bytes; + +void push(bytes chunk, bytes& data) { + if (data.empty()) { + data.swap(chunk); + } else { + data.insert(data.end(), chunk.begin(), chunk.end()); + } +} -- 2.47.2