1From ee4af2ed0b7322884ec4ff537564683c3749b813 Mon Sep 17 00:00:00 2001 2From: Jonathan Wakely <jwakely@redhat.com> 3Date: Thu, 22 Dec 2022 09:56:47 +0000 4Subject: [PATCH] libstdc++: Avoid recursion in __nothrow_wait_cv::wait 5 [PR105730] 6 7The commit r12-5877-g9e18a25331fa25 removed the incorrect 8noexcept-specifier from std::condition_variable::wait and gave the new 9symbol version @@GLIBCXX_3.4.30. It also redefined the original symbol 10std::condition_variable::wait(unique_lock<mutex>&)@GLIBCXX_3.4.11 as an 11alias for a new symbol, __gnu_cxx::__nothrow_wait_cv::wait, which still 12has the incorrect noexcept guarantee. That __nothrow_wait_cv::wait is 13just a wrapper around the real condition_variable::wait which adds 14noexcept and so terminates on a __forced_unwind exception. 15 16This doesn't work on uclibc, possibly due to a dynamic linker bug. When 17__nothrow_wait_cv::wait calls the condition_variable::wait function it 18binds to the alias symbol, which means it just calls itself recursively 19until the stack overflows. 20 21This change avoids the possibility of a recursive call by changing the 22__nothrow_wait_cv::wait function so that instead of calling 23condition_variable::wait it re-implements it. This requires accessing 24the private _M_cond member of condition_variable, so we need to use the 25trick of instantiating a template with the member-pointer of the private 26member. 27 28libstdc++-v3/ChangeLog: 29 30 PR libstdc++/105730 31 * src/c++11/compatibility-condvar.cc (__nothrow_wait_cv::wait): 32 Access private data member of base class and call its wait 33 member. 34 35Signed-off-by: Gleb Mazovetskiy <glex.spb@gmail.com> 36--- 37 .../src/c++11/compatibility-condvar.cc | 22 ++++++++++++++++++- 38 1 file changed, 21 insertions(+), 1 deletion(-) 39 40diff --git a/libstdc++-v3/src/c++11/compatibility-condvar.cc b/libstdc++-v3/src/c++11/compatibility-condvar.cc 41index e3a8b8403ca..3cef3bc0714 100644 42--- a/libstdc++-v3/src/c++11/compatibility-condvar.cc 43+++ b/libstdc++-v3/src/c++11/compatibility-condvar.cc 44@@ -67,6 +67,24 @@ _GLIBCXX_END_NAMESPACE_VERSION 45 && defined(_GLIBCXX_HAVE_SYMVER_SYMBOL_RENAMING_RUNTIME_SUPPORT) 46 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default) 47 { 48+namespace 49+{ 50+ // Pointer-to-member for private std::condition_variable::_M_cond member. 51+ std::__condvar std::condition_variable::* __base_member; 52+ 53+ template<std::__condvar std::condition_variable::*X> 54+ struct cracker 55+ { static std::__condvar std::condition_variable::* value; }; 56+ 57+ // Initializer for this static member also initializes __base_member. 58+ template<std::__condvar std::condition_variable::*X> 59+ std::__condvar std::condition_variable::* 60+ cracker<X>::value = __base_member = X; 61+ 62+ // Explicit instantiation is allowed to access the private member. 63+ template class cracker<&std::condition_variable::_M_cond>; 64+} 65+ 66 struct __nothrow_wait_cv : std::condition_variable 67 { 68 void wait(std::unique_lock<std::mutex>&) noexcept; 69@@ -76,7 +94,9 @@ __attribute__((used)) 70 void 71 __nothrow_wait_cv::wait(std::unique_lock<std::mutex>& lock) noexcept 72 { 73- this->condition_variable::wait(lock); 74+ // In theory this could be simply this->std::condition_variable::wait(lock) 75+ // but with uclibc that binds to the @GLIBCXX_3.4.11 symbol, see PR 105730. 76+ (this->*__base_member).wait(*lock.mutex()); 77 } 78 } // namespace __gnu_cxx 79 80-- 812.31.1 82 83