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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/109703] [12/13/14 Regression] __builtin_unreachable() reached since r13-6915-gbf78b43873b0b7 Date: Wed, 03 May 2023 12:19:45 +0000 [thread overview] Message-ID: <bug-109703-4-NTDDOIkSxb@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-109703-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109703 --- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>: https://gcc.gnu.org/g:cbf6c7a1d16490a1e63e9a5ce00e9a5c44c4c2f2 commit r14-430-gcbf6c7a1d16490a1e63e9a5ce00e9a5c44c4c2f2 Author: Kefu Chai <kefu.chai@scylladb.com> Date: Mon May 1 21:24:26 2023 +0100 libstdc++: Set _M_string_length before calling _M_dispose() [PR109703] This always sets _M_string_length in the constructor for ranges of input iterators, such as stream iterators. We copy from the source range to the local buffer, and then repeatedly reallocate a larger one if necessary. When disposing the old buffer, _M_is_local() is used to tell if the buffer is the local one or not (and so must be deallocated). In addition to comparing the buffer address with the local buffer, _M_is_local() has an optimization hint so that the compiler knows that for a string using the local buffer, there is an invariant that _M_string_length <= _S_local_capacity (added for PR109299 via r13-6915-gbf78b43873b0b7). But we failed to set _M_string_length in the constructor taking a pair of iterators, so the invariant might not hold, and __builtin_unreachable() is reached. This causes UBsan errors, and potentially misoptimization. To ensure the invariant holds, _M_string_length is initialized to zero before doing anything else, so that _M_is_local() doesn't see an uninitialized value. This issue only surfaces when constructing a string with a range of input iterator, and the uninitialized _M_string_length happens to be greater than _S_local_capacity, i.e., 15 for the std::string specialization. libstdc++-v3/ChangeLog: PR libstdc++/109703 * include/bits/basic_string.h (basic_string(Iter, Iter, Alloc)): Initialize _M_string_length. Signed-off-by: Kefu Chai <kefu.chai@scylladb.com> Co-authored-by: Jonathan Wakely <jwakely@redhat.com>
next prev parent reply other threads:[~2023-05-03 12:19 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-05-02 19:05 [Bug libstdc++/109703] New: __builtin_unreachable() reached christian.morales.vega at gmail dot com 2023-05-02 20:10 ` [Bug libstdc++/109703] [13/14 Regression] " pinskia at gcc dot gnu.org 2023-05-02 20:11 ` [Bug libstdc++/109703] [12/13/14 " pinskia at gcc dot gnu.org 2023-05-02 20:14 ` pinskia at gcc dot gnu.org 2023-05-02 20:35 ` [Bug libstdc++/109703] [12/13/14 Regression] __builtin_unreachable() reached since r13-6915-gbf78b43873b0b7 redi at gcc dot gnu.org 2023-05-03 2:00 ` pinskia at gcc dot gnu.org 2023-05-03 12:19 ` cvs-commit at gcc dot gnu.org [this message] 2023-05-03 12:24 ` cvs-commit at gcc dot gnu.org 2023-05-03 13:24 ` cvs-commit at gcc dot gnu.org 2023-05-03 13:25 ` redi at gcc dot gnu.org 2023-05-04 15:43 ` pinskia at gcc dot gnu.org 2023-05-09 11:22 ` redi at gcc dot gnu.org 2023-07-04 16:41 ` redi at gcc dot gnu.org
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