Hi Jonathan (and everyone else), just wanted to ping this patch again. Would be great to get your thoughts!
Thanks, Keno On Mon, Oct 27, 2025 at 3:51 PM Keno Fischer <[email protected]> wrote: > > Hi Jonathan, > > Just wanted to gently ping to see if you've had a chance to take a look. > > Thanks, > Keno > > On Thu, Oct 16, 2025 at 3:15 PM Jonathan Wakely <[email protected]> wrote: > > > > I went travelling for a month on the day you sent the first patch and so I > > missed it. I'll take a look ASAP. > > > > > > > > On Thu, 16 Oct 2025, 19:39 Keno Fischer, <[email protected]> wrote: > >> > >> Hello all, > >> > >> My apologies for not following up on the below earlier, but we're getting > >> additional user complaints about this ABI break, so it's back on my radar. > >> Were there any comments or concerns on my RFC patch below? > >> > >> Keno > >> > >> On Tue, Jul 15, 2025 at 1:37 AM Keno Fischer <[email protected]> wrote: > >> > > >> > The _GLIBCXX_HAVE_TLS flag is an ABI-breaking flag - setting it removes > >> > the > >> > definitions for `set_lock_ptr` (as well as the comptability symbols for > >> > even older ABIs). Try to improve this situation by changing the flag to > >> > retain the old symbols, falling back to the previous behavior if > >> > __once_call > >> > is not set. These symbols are used to forward closure data for the > >> > initialization > >> > from whichever thread ends up winning the pthread_once. The __once_call > >> > is set immediately before the pthread_once and unset (in a destructor) > >> > immediately after. To avoid the case where there may be a nested > >> > __once_proxy > >> > call that uses the old ABI, we also unset __once_call in the success path > >> > after retrieving the pointer. > >> > > >> > Signed-off-by: Keno Fischer <[email protected]> > >> > --- > >> > > >> > Greetings from the Julia Language infrastructure team. For background > >> > behind this patch, we maintain a large number of pre-built binaries for > >> > multiple operating systems, including windows. On windows, we generally > >> > follow the MSYS2-provided mingw ABI for our binaries (even though we > >> > maintain our own toolchains to actually generate the binaries). > >> > At some point recently, msys2 switched to building gcc with --enable-tls. > >> > This caused an ABI break for us, making our old binaries no longer > >> > work in newer msys2 environments because. I have two distinct questions > >> > here: > >> > > >> > 1. Is there something obviously wrong with this approach that I'm > >> > missing? > >> > > >> > 2. Is this appropriate for upstream inclusion? > >> > > >> > We're fine if the answer to #2 is no - in which case we'd ship a patched > >> > libstdc++ version with this patch for a while until all binaries that > >> > have shipped with the old ABI have filtered out as part of our usual > >> > replacement cycle. Of course, if this approach doesn't work, we'd > >> > appreciate any thoughts on how to maintain ABI compatibility here, even > >> > temporarily. > >> > > >> > (I think the diffstat looks messier than it is because of the indentation > >> > changes - the basic changes is just to merge the two __once_proxy > >> > calls together, checking if __once_call is set, using it if so and > >> > falling > >> > back to the old ABI if not). > >> > > >> > libstdc++-v3/src/c++11/mutex.cc | 111 +++++++++++++++++--------------- > >> > 1 file changed, 59 insertions(+), 52 deletions(-) > >> > > >> > diff --git a/libstdc++-v3/src/c++11/mutex.cc > >> > b/libstdc++-v3/src/c++11/mutex.cc > >> > index d5da5c66ae9..4be64633315 100644 > >> > --- a/libstdc++-v3/src/c++11/mutex.cc > >> > +++ b/libstdc++-v3/src/c++11/mutex.cc > >> > @@ -23,6 +23,7 @@ > >> > // <http://www.gnu.org/licenses/>. > >> > > >> > #include <mutex> > >> > +#include <bits/std_function.h> // std::function > >> > > >> > #ifdef _GLIBCXX_HAS_GTHREADS > >> > > >> > @@ -30,30 +31,17 @@ namespace std _GLIBCXX_VISIBILITY(default) > >> > { > >> > _GLIBCXX_BEGIN_NAMESPACE_VERSION > >> > > >> > -#ifdef _GLIBCXX_HAVE_TLS > >> > - __thread void* __once_callable; > >> > - __thread void (*__once_call)(); > >> > +// Explicit instantiation due to -fno-implicit-instantiation. > >> > +template class function<void()>; > >> > > >> > - extern "C" void __once_proxy() > >> > - { > >> > - // The caller stored a function pointer in __once_call. If it > >> > requires > >> > - // any state, it gets it from __once_callable. > >> > - __once_call(); > >> > - } > >> > +function<void()> __once_functor; > >> > > >> > -#else // ! TLS > >> > - > >> > - // Explicit instantiation due to -fno-implicit-instantiation. > >> > - template class function<void()>; > >> > - > >> > - function<void()> __once_functor; > >> > - > >> > - mutex& > >> > - __get_once_mutex() > >> > - { > >> > - static mutex once_mutex; > >> > - return once_mutex; > >> > - } > >> > +mutex& > >> > +__get_once_mutex() > >> > +{ > >> > + static mutex once_mutex; > >> > + return once_mutex; > >> > +} > >> > > >> > namespace > >> > { > >> > @@ -66,41 +54,60 @@ namespace > >> > } > >> > } > >> > > >> > - // code linked against ABI 3.4.12 and later uses this > >> > - void > >> > - __set_once_functor_lock_ptr(unique_lock<mutex>* __ptr) > >> > - { > >> > - (void) set_lock_ptr(__ptr); > >> > - } > >> > +// code linked against ABI 3.4.12 and later uses this > >> > +void > >> > +__set_once_functor_lock_ptr(unique_lock<mutex>* __ptr) > >> > +{ > >> > + (void) set_lock_ptr(__ptr); > >> > +} > >> > > >> > - // unsafe - retained for compatibility with ABI 3.4.11 > >> > - unique_lock<mutex>& > >> > - __get_once_functor_lock() > >> > - { > >> > - static unique_lock<mutex> once_functor_lock(__get_once_mutex(), > >> > defer_lock); > >> > - return once_functor_lock; > >> > - } > >> > +// unsafe - retained for compatibility with ABI 3.4.11 > >> > +unique_lock<mutex>& > >> > +__get_once_functor_lock() > >> > +{ > >> > + static unique_lock<mutex> once_functor_lock(__get_once_mutex(), > >> > defer_lock); > >> > + return once_functor_lock; > >> > +} > >> > > >> > - // This is called via pthread_once while __get_once_mutex() is locked. > >> > - extern "C" void > >> > - __once_proxy() > >> > - { > >> > - // Get the callable out of the global functor. > >> > - function<void()> callable = std::move(__once_functor); > >> > - > >> > - // Then unlock the global mutex > >> > - if (unique_lock<mutex>* lock = set_lock_ptr(nullptr)) > >> > - { > >> > - // Caller is using the new ABI and provided a pointer to its lock. > >> > - lock->unlock(); > >> > +#ifdef _GLIBCXX_HAVE_TLS > >> > + __thread void* __once_callable; > >> > + __thread void (*__once_call)(); > >> > +#endif > >> > + > >> > +extern "C" void > >> > +__once_proxy() > >> > +{ > >> > +#ifdef _GLIBCXX_HAVE_TLS > >> > + if (__once_call) { > >> > + void (*this_once_call)() = __once_call; > >> > + // Reset __once_call early in case of a nested call to > >> > __once_proxy > >> > + // with the old ABI. > >> > + __once_call = NULL; > >> > + return this_once_call(); > >> > } > >> > - else > >> > - __get_once_functor_lock().unlock(); // global lock > >> > > >> > - // Finally, invoke the callable. > >> > - callable(); > >> > + // For compatibility with callers linked against > >> > non-_GLIBCXX_HAVE_TLS ABI, > >> > + // we fall through here to the old behavior. > >> > +#endif > >> > + > >> > + // If the caller is not using _GLIBCXX_HAVE_TLS, this was called > >> > + // via pthread_once while __get_once_mutex() is locked. > >> > + > >> > + // Get the callable out of the global functor. > >> > + function<void()> callable = std::move(__once_functor); > >> > + > >> > + // Then unlock the global mutex > >> > + if (unique_lock<mutex>* lock = set_lock_ptr(nullptr)) > >> > + { > >> > + // Caller is using the new ABI and provided a pointer to its lock. > >> > + lock->unlock(); > >> > } > >> > -#endif // ! TLS > >> > + else > >> > + __get_once_functor_lock().unlock(); // global lock > >> > + > >> > + // Finally, invoke the callable. > >> > + callable(); > >> > +} > >> > > >> > _GLIBCXX_END_NAMESPACE_VERSION > >> > } // namespace std > >> > -- > >> > 2.43.0
