1*4882a593SmuzhiyunFrom ee4af2ed0b7322884ec4ff537564683c3749b813 Mon Sep 17 00:00:00 2001 2*4882a593SmuzhiyunFrom: Jonathan Wakely <jwakely@redhat.com> 3*4882a593SmuzhiyunDate: Thu, 22 Dec 2022 09:56:47 +0000 4*4882a593SmuzhiyunSubject: [PATCH] libstdc++: Avoid recursion in __nothrow_wait_cv::wait 5*4882a593Smuzhiyun [PR105730] 6*4882a593Smuzhiyun 7*4882a593SmuzhiyunThe commit r12-5877-g9e18a25331fa25 removed the incorrect 8*4882a593Smuzhiyunnoexcept-specifier from std::condition_variable::wait and gave the new 9*4882a593Smuzhiyunsymbol version @@GLIBCXX_3.4.30. It also redefined the original symbol 10*4882a593Smuzhiyunstd::condition_variable::wait(unique_lock<mutex>&)@GLIBCXX_3.4.11 as an 11*4882a593Smuzhiyunalias for a new symbol, __gnu_cxx::__nothrow_wait_cv::wait, which still 12*4882a593Smuzhiyunhas the incorrect noexcept guarantee. That __nothrow_wait_cv::wait is 13*4882a593Smuzhiyunjust a wrapper around the real condition_variable::wait which adds 14*4882a593Smuzhiyunnoexcept and so terminates on a __forced_unwind exception. 15*4882a593Smuzhiyun 16*4882a593SmuzhiyunThis doesn't work on uclibc, possibly due to a dynamic linker bug. When 17*4882a593Smuzhiyun__nothrow_wait_cv::wait calls the condition_variable::wait function it 18*4882a593Smuzhiyunbinds to the alias symbol, which means it just calls itself recursively 19*4882a593Smuzhiyununtil the stack overflows. 20*4882a593Smuzhiyun 21*4882a593SmuzhiyunThis change avoids the possibility of a recursive call by changing the 22*4882a593Smuzhiyun__nothrow_wait_cv::wait function so that instead of calling 23*4882a593Smuzhiyuncondition_variable::wait it re-implements it. This requires accessing 24*4882a593Smuzhiyunthe private _M_cond member of condition_variable, so we need to use the 25*4882a593Smuzhiyuntrick of instantiating a template with the member-pointer of the private 26*4882a593Smuzhiyunmember. 27*4882a593Smuzhiyun 28*4882a593Smuzhiyunlibstdc++-v3/ChangeLog: 29*4882a593Smuzhiyun 30*4882a593Smuzhiyun PR libstdc++/105730 31*4882a593Smuzhiyun * src/c++11/compatibility-condvar.cc (__nothrow_wait_cv::wait): 32*4882a593Smuzhiyun Access private data member of base class and call its wait 33*4882a593Smuzhiyun member. 34*4882a593Smuzhiyun 35*4882a593SmuzhiyunSigned-off-by: Gleb Mazovetskiy <glex.spb@gmail.com> 36*4882a593Smuzhiyun--- 37*4882a593Smuzhiyun .../src/c++11/compatibility-condvar.cc | 22 ++++++++++++++++++- 38*4882a593Smuzhiyun 1 file changed, 21 insertions(+), 1 deletion(-) 39*4882a593Smuzhiyun 40*4882a593Smuzhiyundiff --git a/libstdc++-v3/src/c++11/compatibility-condvar.cc b/libstdc++-v3/src/c++11/compatibility-condvar.cc 41*4882a593Smuzhiyunindex e3a8b8403ca..3cef3bc0714 100644 42*4882a593Smuzhiyun--- a/libstdc++-v3/src/c++11/compatibility-condvar.cc 43*4882a593Smuzhiyun+++ b/libstdc++-v3/src/c++11/compatibility-condvar.cc 44*4882a593Smuzhiyun@@ -67,6 +67,24 @@ _GLIBCXX_END_NAMESPACE_VERSION 45*4882a593Smuzhiyun && defined(_GLIBCXX_HAVE_SYMVER_SYMBOL_RENAMING_RUNTIME_SUPPORT) 46*4882a593Smuzhiyun namespace __gnu_cxx _GLIBCXX_VISIBILITY(default) 47*4882a593Smuzhiyun { 48*4882a593Smuzhiyun+namespace 49*4882a593Smuzhiyun+{ 50*4882a593Smuzhiyun+ // Pointer-to-member for private std::condition_variable::_M_cond member. 51*4882a593Smuzhiyun+ std::__condvar std::condition_variable::* __base_member; 52*4882a593Smuzhiyun+ 53*4882a593Smuzhiyun+ template<std::__condvar std::condition_variable::*X> 54*4882a593Smuzhiyun+ struct cracker 55*4882a593Smuzhiyun+ { static std::__condvar std::condition_variable::* value; }; 56*4882a593Smuzhiyun+ 57*4882a593Smuzhiyun+ // Initializer for this static member also initializes __base_member. 58*4882a593Smuzhiyun+ template<std::__condvar std::condition_variable::*X> 59*4882a593Smuzhiyun+ std::__condvar std::condition_variable::* 60*4882a593Smuzhiyun+ cracker<X>::value = __base_member = X; 61*4882a593Smuzhiyun+ 62*4882a593Smuzhiyun+ // Explicit instantiation is allowed to access the private member. 63*4882a593Smuzhiyun+ template class cracker<&std::condition_variable::_M_cond>; 64*4882a593Smuzhiyun+} 65*4882a593Smuzhiyun+ 66*4882a593Smuzhiyun struct __nothrow_wait_cv : std::condition_variable 67*4882a593Smuzhiyun { 68*4882a593Smuzhiyun void wait(std::unique_lock<std::mutex>&) noexcept; 69*4882a593Smuzhiyun@@ -76,7 +94,9 @@ __attribute__((used)) 70*4882a593Smuzhiyun void 71*4882a593Smuzhiyun __nothrow_wait_cv::wait(std::unique_lock<std::mutex>& lock) noexcept 72*4882a593Smuzhiyun { 73*4882a593Smuzhiyun- this->condition_variable::wait(lock); 74*4882a593Smuzhiyun+ // In theory this could be simply this->std::condition_variable::wait(lock) 75*4882a593Smuzhiyun+ // but with uclibc that binds to the @GLIBCXX_3.4.11 symbol, see PR 105730. 76*4882a593Smuzhiyun+ (this->*__base_member).wait(*lock.mutex()); 77*4882a593Smuzhiyun } 78*4882a593Smuzhiyun } // namespace __gnu_cxx 79*4882a593Smuzhiyun 80*4882a593Smuzhiyun-- 81*4882a593Smuzhiyun2.31.1 82*4882a593Smuzhiyun 83