https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118105
--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:fa6549c1f0e75ff33cb641d98af72ee354b04bbe commit r15-6691-gfa6549c1f0e75ff33cb641d98af72ee354b04bbe Author: Jonathan Wakely <jwak...@redhat.com> Date: Wed Dec 18 12:57:14 2024 +0000 libstdc++: Handle errors from strxfrm in std::collate::transform [PR85824] std::regex builds a cache of equivalence classes by calling std::regex_traits<char>::transform_primary(c) for every char, which then calls std::collate<char>::transform which calls strxfrm. On several targets strxfrm fails for non-ASCII characters. Because strxfrm has no return value reserved to indicate an error, some implementations return INT_MAX or SIZE_MAX. This causes std::collate::transform to try to allocate a huge buffer, which is either very slow or throws std::bad_alloc. We should check errno after calling strxfrm to detect errors and then throw a more appropriate exception instead of trying to allocate a huge buffer. Unfortunately the std::collate<C>::_M_transform function has a non-throwing exception specifier, so we can't do the error handling there. As well as checking errno, this patch changes std::collate::do_transform to use __builtin_alloca for small inputs, and to use RAII to deallocate the buffers used for large inputs. This change isn't sufficient to fix the three std::regex bugs caused by the lack of error handling in std::collate::do_transform, we also need to make std::regex_traits::transform_primary handle exceptions. This change also attempts to make transform_primary closer to the effects described in the standard, by not even attempting to use std::collate if the locale's std::collate facet has been replaced (see PR 118105). Implementing the correct effects for transform_primary requires RTTI, so that we don't use some user-defined std::collate facet with unknown semantics. When -fno-rtti is used transform_primary just returns an empty string, making equivalence classes unusable in std::basic_regex. That's not ideal, but I don't have any better ideas. I'm unsure if std::regex_traits<C>::transform_primary is supposed to convert the string to lower case or not. The general regex traits requirements ([re.req] p20) do say "when character case is not considered" but the specification for the std::regex_traits<char> and std::regex_traits<wchar_t> specializations ([re.traits] p7) don't say anything about that. With the r15-6317-geb339c29ee42aa change, transform_primary is not called unless the regex actually uses an equivalence class. But using an equivalence class would still fail (or be incredibly slow) on some targets. With this commit, equivalence classes should be usable on all targets, without excessive memory allocations. Arguably, we should not even try to call transform_primary for any char values over 127, since they're never valid in locales that use UTF-8 or 7-bit ASCII, and probably for other charsets too. Handling 128 exceptions for every std::regex compilation is very inefficient, but at least it now works instead of failing with std::bad_alloc, and no longer allocates 128 x 2GB. Maybe for C++26 we could check the locale's std::text_encoding and use that to decide whether to cache equivalence classes for char values over 127. libstdc++-v3/ChangeLog: PR libstdc++/85824 PR libstdc++/94409 PR libstdc++/98723 PR libstdc++/118105 * include/bits/locale_classes.tcc (collate::do_transform): Check errno after calling _M_transform. Use RAII type to manage the buffer and to restore errno. * include/bits/regex.h (regex_traits::transform_primary): Handle exceptions from std::collate::transform and do not try to use std::collate for user-defined facets.
