I noticed a -Wmaybe-uninitialized warning for this function, which turns out to be correct. If the caller passes a valid std::ios_base::seekdir value then there's no problem, but if they pass std::seekdir(999) then we don't initialize the __base variable before adding it to __off.
Rather than initialize it to an arbitrary value, we should return an error. Also add [[unlikely]] attributes to the paths that return an error. libstdc++-v3/ChangeLog: * include/std/spanstream (basic_spanbuf::seekoff): Return an error for invalid seekdir values. --- Tested x86_64-linux. Pushed to trunk. libstdc++-v3/include/std/spanstream | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/libstdc++-v3/include/std/spanstream b/libstdc++-v3/include/std/spanstream index 98ad3fa856a..23a340a746e 100644 --- a/libstdc++-v3/include/std/spanstream +++ b/libstdc++-v3/include/std/spanstream @@ -168,7 +168,7 @@ template<typename _CharT, typename _Traits> } else { - off_type __base; + off_type __base{}; __which &= (ios_base::in|ios_base::out); if (__which == ios_base::out) @@ -182,11 +182,13 @@ template<typename _CharT, typename _Traits> } else if (__way == ios_base::end) __base = _M_buf.size(); - - if (__builtin_add_overflow(__base, __off, &__off)) + else /* way is not ios::beg, ios::cur, or ios::end */ [[unlikely]] return __ret; - if (__off < 0 || __off > _M_buf.size()) + if (__builtin_add_overflow(__base, __off, &__off)) [[unlikely]] + return __ret; + + if (__off < 0 || __off > _M_buf.size()) [[unlikely]] return __ret; if (__which & ios_base::in) -- 2.47.1