* [PATCH 1/2] libstdc++: Revert to old std::call_once implementation [PR 99341]
@ 2021-03-12 17:45 Jonathan Wakely
2021-03-12 17:46 ` [PATCH 2/2] libstdc++: Remove symbols for new " Jonathan Wakely
0 siblings, 1 reply; 3+ messages in thread
From: Jonathan Wakely @ 2021-03-12 17:45 UTC (permalink / raw)
To: libstdc++, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 1960 bytes --]
The new std::call_once implementation is not backwards compatible,
contrary to my intention. Because std::once_flag::_M_active() doesn't
write glibc's "fork generation" into the pthread_once_t object, it's
possible for glibc and libstdc++ to run two active executions
concurrently. This violates the primary invariant of the feature!
This patch reverts std::once_flag and std::call_once to the old
implementation that uses pthread_once. This means PR 66146 is a problem
again, but glibc has been changed to solve that. A new API similar to
pthread_once but supporting failure and resetting the pthread_once_t
will be proposed for inclusion in glibc and other C libraries.
This change doesn't simply revert r11-4691 because I want to retain the
new implementation for non-ghtreads targets (which didn't previously
support std::call_once at all, so there's no backwards compatibility
concern). This also leaves the new std::call_once::_M_activate() and
std::call_once::_M_finish(bool) symbols present in libstdc++.so.6 so
that code already compiled against GCC 11 can still use them. Those
symbols will be removed in a subsequent commit (which distros can choose
to temporarily revert if needed).
libstdc++-v3/ChangeLog:
PR libstdc++/99341
* include/std/mutex [_GLIBCXX_HAVE_LINUX_FUTEX] (once_flag):
Revert to pthread_once_t implementation.
[_GLIBCXX_HAVE_LINUX_FUTEX] (call_once): Likewise.
* src/c++11/mutex.cc [_GLIBCXX_HAVE_LINUX_FUTEX]
(struct __once_flag_compat): New type matching the reverted
implementation of once_flag using futexes.
(once_flag::_M_activate): Remove, replace with ...
(_ZNSt9once_flag11_M_activateEv): ... alias symbol.
(once_flag::_M_finish): Remove, replace with ...
(_ZNSt9once_flag9_M_finishEb): ... alias symbol.
* testsuite/30_threads/call_once/66146.cc: Removed.
Tested x86_64-linux, powerpc64-linux and powerpc64le-linux, but not yet
committed (it's not really appropriate for a last-minute Friday
change!)
[-- Attachment #2: patch.txt --]
[-- Type: text/plain, Size: 15518 bytes --]
commit c5ae3f030cc24ec73311f1ff85b8ebdf8551479c
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Fri Mar 12 11:47:20 2021
libstdc++: Revert to old std::call_once implementation [PR 99341]
The new std::call_once implementation is not backwards compatible,
contrary to my intention. Because std::once_flag::_M_active() doesn't
write glibc's "fork generation" into the pthread_once_t object, it's
possible for glibc and libstdc++ to run two active executions
concurrently. This violates the primary invariant of the feature!
This patch reverts std::once_flag and std::call_once to the old
implementation that uses pthread_once. This means PR 66146 is a problem
again, but glibc has been changed to solve that. A new API similar to
pthread_once but supporting failure and resetting the pthread_once_t
will be proposed for inclusion in glibc and other C libraries.
This change doesn't simply revert r11-4691 because I want to retain the
new implementation for non-ghtreads targets (which didn't previously
support std::call_once at all, so there's no backwards compatibility
concern). This also leaves the new std::call_once::_M_activate() and
std::call_once::_M_finish(bool) symbols present in libstdc++.so.6 so
that code already compiled against GCC 11 can still use them. Those
symbols will be removed in a subsequent commit (which distros can choose
to temporarily revert if needed).
libstdc++-v3/ChangeLog:
PR libstdc++/99341
* include/std/mutex [_GLIBCXX_HAVE_LINUX_FUTEX] (once_flag):
Revert to pthread_once_t implementation.
[_GLIBCXX_HAVE_LINUX_FUTEX] (call_once): Likewise.
* src/c++11/mutex.cc [_GLIBCXX_HAVE_LINUX_FUTEX]
(struct __once_flag_compat): New type matching the reverted
implementation of once_flag using futexes.
(once_flag::_M_activate): Remove, replace with ...
(_ZNSt9once_flag11_M_activateEv): ... alias symbol.
(once_flag::_M_finish): Remove, replace with ...
(_ZNSt9once_flag9_M_finishEb): ... alias symbol.
* testsuite/30_threads/call_once/66146.cc: Removed.
diff --git a/libstdc++-v3/include/std/mutex b/libstdc++-v3/include/std/mutex
index f96c48e88ec..b6a595237bf 100644
--- a/libstdc++-v3/include/std/mutex
+++ b/libstdc++-v3/include/std/mutex
@@ -669,6 +669,123 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
};
#endif // C++17
+#ifdef _GLIBCXX_HAS_GTHREADS
+ /// Flag type used by std::call_once
+ struct once_flag
+ {
+ constexpr once_flag() noexcept = default;
+
+ /// Deleted copy constructor
+ once_flag(const once_flag&) = delete;
+ /// Deleted assignment operator
+ once_flag& operator=(const once_flag&) = delete;
+
+ private:
+ // For gthreads targets a pthread_once_t is used with pthread_once, but
+ // for most targets this doesn't work correctly for exceptional executions.
+ __gthread_once_t _M_once = __GTHREAD_ONCE_INIT;
+
+ struct _Prepare_execution;
+
+ template<typename _Callable, typename... _Args>
+ friend void
+ call_once(once_flag& __once, _Callable&& __f, _Args&&... __args);
+ };
+
+ /// @cond undocumented
+# ifdef _GLIBCXX_HAVE_TLS
+ // If TLS is available use thread-local state for the type-erased callable
+ // that is being run by std::call_once in the current thread.
+ extern __thread void* __once_callable;
+ extern __thread void (*__once_call)();
+
+ // RAII type to set up state for pthread_once call.
+ struct once_flag::_Prepare_execution
+ {
+ template<typename _Callable>
+ explicit
+ _Prepare_execution(_Callable& __c)
+ {
+ // Store address in thread-local pointer:
+ __once_callable = std::__addressof(__c);
+ // Trampoline function to invoke the closure via thread-local pointer:
+ __once_call = [] { (*static_cast<_Callable*>(__once_callable))(); };
+ }
+
+ ~_Prepare_execution()
+ {
+ // PR libstdc++/82481
+ __once_callable = nullptr;
+ __once_call = nullptr;
+ }
+
+ _Prepare_execution(const _Prepare_execution&) = delete;
+ _Prepare_execution& operator=(const _Prepare_execution&) = delete;
+ };
+
+# else
+ // Without TLS use a global std::mutex and store the callable in a
+ // global std::function.
+ extern function<void()> __once_functor;
+
+ extern void
+ __set_once_functor_lock_ptr(unique_lock<mutex>*);
+
+ extern mutex&
+ __get_once_mutex();
+
+ // RAII type to set up state for pthread_once call.
+ struct once_flag::_Prepare_execution
+ {
+ template<typename _Callable>
+ explicit
+ _Prepare_execution(_Callable& __c)
+ {
+ // Store the callable in the global std::function
+ __once_functor = __c;
+ __set_once_functor_lock_ptr(&_M_functor_lock);
+ }
+
+ ~_Prepare_execution()
+ {
+ if (_M_functor_lock)
+ __set_once_functor_lock_ptr(nullptr);
+ }
+
+ private:
+ // XXX This deadlocks if used recursively (PR 97949)
+ unique_lock<mutex> _M_functor_lock{__get_once_mutex()};
+
+ _Prepare_execution(const _Prepare_execution&) = delete;
+ _Prepare_execution& operator=(const _Prepare_execution&) = delete;
+ };
+# endif
+ /// @endcond
+
+ // This function is passed to pthread_once by std::call_once.
+ // It runs __once_call() or __once_functor().
+ extern "C" void __once_proxy(void);
+
+ /// Invoke a callable and synchronize with other calls using the same flag
+ template<typename _Callable, typename... _Args>
+ void
+ call_once(once_flag& __once, _Callable&& __f, _Args&&... __args)
+ {
+ // Closure type that runs the function
+ auto __callable = [&] {
+ std::__invoke(std::forward<_Callable>(__f),
+ std::forward<_Args>(__args)...);
+ };
+
+ once_flag::_Prepare_execution __exec(__callable);
+
+ // XXX pthread_once does not reset the flag if an exception is thrown.
+ if (int __e = __gthread_once(&__once._M_once, &__once_proxy))
+ __throw_system_error(__e);
+ }
+
+#else // _GLIBCXX_HAS_GTHREADS
+
/// Flag type used by std::call_once
struct once_flag
{
@@ -682,27 +799,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
private:
// There are two different std::once_flag interfaces, abstracting four
// different implementations.
- // The preferred interface uses the _M_activate() and _M_finish(bool)
- // member functions (introduced in GCC 11), which start and finish an
- // active execution respectively. See [thread.once.callonce] in C++11
- // for the definition of active/passive/returning/exceptional executions.
- // This interface is supported for Linux (using atomics and futexes) and
- // for single-threaded targets with no gthreads support.
- // For other targets a pthread_once_t is used with pthread_once, but that
- // doesn't work correctly for exceptional executions. That interface
- // uses an object of type _Prepare_execution and a lambda expression.
-#if defined _GLIBCXX_HAVE_LINUX_FUTEX || ! defined _GLIBCXX_HAS_GTHREADS
+ // The single-threaded interface uses the _M_activate() and _M_finish(bool)
+ // functions, which start and finish an active execution respectively.
+ // See [thread.once.callonce] in C++11 for the definition of
+ // active/passive/returning/exceptional executions.
enum _Bits : int { _Init = 0, _Active = 1, _Done = 2 };
int _M_once = _Bits::_Init;
- // Non-blocking check to see if all executions will be passive now.
+ // Check to see if all executions will be passive now.
bool
_M_passive() const noexcept;
- // Attempts to begin an active execution. Blocks until it either:
- // - returns true if an active execution has started on this thread, or
- // - returns false if a returning execution happens on another thread.
+ // Attempts to begin an active execution.
bool _M_activate();
// Must be called to complete an active execution.
@@ -723,18 +832,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
once_flag& _M_flag;
bool _M_returning = false;
};
-#else
- __gthread_once_t _M_once = __GTHREAD_ONCE_INIT;
-
- struct _Prepare_execution;
-#endif // ! GTHREADS
template<typename _Callable, typename... _Args>
friend void
call_once(once_flag& __once, _Callable&& __f, _Args&&... __args);
};
-#if ! defined _GLIBCXX_HAS_GTHREADS
// Inline definitions of std::once_flag members for single-threaded targets.
inline bool
@@ -759,94 +862,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
once_flag::_M_finish(bool __returning) noexcept
{ _M_once = __returning ? _Bits::_Done : _Bits::_Init; }
-#elif defined _GLIBCXX_HAVE_LINUX_FUTEX
-
- // Define this inline to make passive executions fast.
- inline bool
- once_flag::_M_passive() const noexcept
- {
- if (__gnu_cxx::__is_single_threaded())
- return _M_once == _Bits::_Done;
- else
- return __atomic_load_n(&_M_once, __ATOMIC_ACQUIRE) == _Bits::_Done;
- }
-
-#else // GTHREADS && ! FUTEX
-
- /// @cond undocumented
-# ifdef _GLIBCXX_HAVE_TLS
- // If TLS is available use thread-local state for the type-erased callable
- // that is being run by std::call_once in the current thread.
- extern __thread void* __once_callable;
- extern __thread void (*__once_call)();
-# else
- // Without TLS use a global std::mutex and store the callable in a
- // global std::function.
- extern function<void()> __once_functor;
-
- extern void
- __set_once_functor_lock_ptr(unique_lock<mutex>*);
-
- extern mutex&
- __get_once_mutex();
-# endif
-
- // This function is passed to pthread_once by std::call_once.
- // It runs __once_call() or __once_functor().
- extern "C" void __once_proxy(void);
-
- // RAII type to set up state for pthread_once call.
- struct once_flag::_Prepare_execution
- {
-#ifdef _GLIBCXX_HAVE_TLS
- template<typename _Callable>
- explicit
- _Prepare_execution(_Callable& __c)
- {
- // Store address in thread-local pointer:
- __once_callable = std::__addressof(__c);
- // Trampoline function to invoke the closure via thread-local pointer:
- __once_call = [] { (*static_cast<_Callable*>(__once_callable))(); };
- }
-
- ~_Prepare_execution()
- {
- // PR libstdc++/82481
- __once_callable = nullptr;
- __once_call = nullptr;
- }
-#else // ! TLS
- template<typename _Callable>
- explicit
- _Prepare_execution(_Callable& __c)
- {
- // Store the callable in the global std::function
- __once_functor = __c;
- __set_once_functor_lock_ptr(&_M_functor_lock);
- }
-
- ~_Prepare_execution()
- {
- if (_M_functor_lock)
- __set_once_functor_lock_ptr(nullptr);
- }
-
- private:
- unique_lock<mutex> _M_functor_lock{__get_once_mutex()};
-#endif // ! TLS
-
- _Prepare_execution(const _Prepare_execution&) = delete;
- _Prepare_execution& operator=(const _Prepare_execution&) = delete;
- };
- /// @endcond
-#endif
-
/// Invoke a callable and synchronize with other calls using the same flag
template<typename _Callable, typename... _Args>
- void
+ inline void
call_once(once_flag& __once, _Callable&& __f, _Args&&... __args)
{
-#if defined _GLIBCXX_HAVE_LINUX_FUTEX || ! defined _GLIBCXX_HAS_GTHREADS
if (__once._M_passive())
return;
else if (__once._M_activate())
@@ -861,20 +881,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// __f(__args...) did not throw
__exec._M_returning = true;
}
-#else
- // Closure type that runs the function
- auto __callable = [&] {
- std::__invoke(std::forward<_Callable>(__f),
- std::forward<_Args>(__args)...);
- };
-
- once_flag::_Prepare_execution __exec(__callable);
-
- // XXX pthread_once does not reset the flag if an exception is thrown.
- if (int __e = __gthread_once(&__once._M_once, &__once_proxy))
- __throw_system_error(__e);
-#endif
}
+#endif // _GLIBCXX_HAS_GTHREADS
// @} group mutexes
_GLIBCXX_END_NAMESPACE_VERSION
diff --git a/libstdc++-v3/src/c++11/mutex.cc b/libstdc++-v3/src/c++11/mutex.cc
index 79db3180a68..3b48998b7e4 100644
--- a/libstdc++-v3/src/c++11/mutex.cc
+++ b/libstdc++-v3/src/c++11/mutex.cc
@@ -26,13 +26,27 @@
#ifdef _GLIBCXX_HAS_GTHREADS
+#if defined _GLIBCXX_SHARED && ! _GLIBCXX_INLINE_VERSION
+
#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
-#include <syscall.h>
-#include <unistd.h>
-#include <limits.h>
+# include <syscall.h>
+# include <unistd.h>
+# include <limits.h>
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+struct __once_flag_compat
+{
+ enum _Bits : int { _Init = 0, _Active = 1, _Done = 2 };
+ int _M_once = 0;
+ bool _M_activate();
+ void _M_finish(bool returning) noexcept;
+};
bool
-std::once_flag::_M_activate()
+__once_flag_compat::_M_activate()
{
if (__gnu_cxx::__is_single_threaded())
{
@@ -64,7 +78,7 @@ std::once_flag::_M_activate()
}
void
-std::once_flag::_M_finish(bool returning) noexcept
+std::__once_flag_compat::_M_finish(bool returning) noexcept
{
const int newval = returning ? _Bits::_Done : _Bits::_Init;
if (__gnu_cxx::__is_single_threaded())
@@ -83,7 +97,18 @@ std::once_flag::_M_finish(bool returning) noexcept
}
}
-#endif // ! FUTEX
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wattribute-alias"
+extern "C" bool _ZNSt9once_flag11_M_activateEv()
+ __attribute__((alias ("_ZNSt18__once_flag_compat11_M_activateEv")));
+extern "C" void _ZNSt9once_flag9_M_finishEb() noexcept
+ __attribute__((alias ("_ZNSt18__once_flag_compat9_M_finishEb")));
+#pragma GCC diagnostic pop
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+#endif // FUTEX
+#endif // ONCE_FLAG_COMPAT && SHARED && ! INLINE_VERSION
namespace std _GLIBCXX_VISIBILITY(default)
{
diff --git a/libstdc++-v3/testsuite/30_threads/call_once/66146.cc b/libstdc++-v3/testsuite/30_threads/call_once/66146.cc
deleted file mode 100644
index f5529373a05..00000000000
--- a/libstdc++-v3/testsuite/30_threads/call_once/66146.cc
+++ /dev/null
@@ -1,53 +0,0 @@
-// Copyright (C) 2020-2021 Free Software Foundation, Inc.
-//
-// This file is part of the GNU ISO C++ Library. This library is free
-// software; you can redistribute it and/or modify it under the
-// terms of the GNU General Public License as published by the
-// Free Software Foundation; either version 3, or (at your option)
-// any later version.
-
-// This library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
-// GNU General Public License for more details.
-
-// You should have received a copy of the GNU General Public License along
-// with this library; see the file COPYING3. If not see
-// <http://www.gnu.org/licenses/>.
-
-// { dg-do run { target c++11 } }
-// { dg-additional-options "-pthread" { target pthread } }
-
-// Currently std::call_once is broken for gthreads targets without futexes:
-// { dg-skip-if "see PR 66146" { gthreads && { ! futex } } }
-
-#include <mutex>
-#include <cstdlib>
-#include <testsuite_hooks.h>
-
-void
-test01()
-{
- std::once_flag once;
- int counter = 0;
- for (int i = 0; i < 10; ++i)
- {
- try
- {
- std::call_once(once, [&]{ if (i < 3) throw i; ++counter; });
- VERIFY(i >= 3);
- }
- catch (int ex)
- {
- VERIFY(i < 3);
- }
- }
- VERIFY(counter == 1);
- std::call_once(once, []{ std::abort(); });
-}
-
-int
-main()
-{
- test01();
-}
^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH 2/2] libstdc++: Remove symbols for new std::call_once implementation [PR 99341]
2021-03-12 17:45 [PATCH 1/2] libstdc++: Revert to old std::call_once implementation [PR 99341] Jonathan Wakely
@ 2021-03-12 17:46 ` Jonathan Wakely
2021-03-16 12:40 ` Jonathan Wakely
0 siblings, 1 reply; 3+ messages in thread
From: Jonathan Wakely @ 2021-03-12 17:46 UTC (permalink / raw)
To: libstdc++, gcc-patches
[-- Attachment #1: Type: text/plain, Size: 1183 bytes --]
This removes the new symbols added for the new futex-based
std::call_once implementation. These symbols were new on trunk, so not
in any released version. However, they are already present in some
beta distro releases (Fedora Linux 34) and in Fedora Linux rawhide. This
change can be locally reverted by distros that need to keep the symbols
present until affected packages have been rebuilt.
libstdc++-v3/ChangeLog:
PR libstdc++/99341
* config/abi/post/aarch64-linux-gnu/baseline_symbols.txt: Remove
std::once_flag symbols.
* config/abi/post/ia64-linux-gnu/baseline_symbols.txt: Likewise.
* config/abi/post/m68k-linux-gnu/baseline_symbols.txt: Likewise.
* config/abi/post/riscv64-linux-gnu/baseline_symbols.txt:
Likewise.
* config/abi/pre/gnu.ver: Likewise.
* src/c++11/mutex.cc [_GLIBCXX_HAVE_LINUX_FUTEX]
(struct __once_flag_compat): Remove.
(_ZNSt9once_flag11_M_activateEv): Remove.
(_ZNSt9once_flag9_M_finishEb): Remove.
Tested x86_64-linux, powerpc64-linux and powerpc64le-linux, but not yet
committed (it's not really appropriate for a last-minute Friday
change!)
[-- Attachment #2: patch.txt --]
[-- Type: text/x-patch, Size: 8548 bytes --]
commit 621a5b5bcb27b0806af020beb1be8e75e050d308
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Fri Mar 12 11:47:20 2021
libstdc++: Remove symbols for new std::call_once implementation [PR 99341]
This removes the new symbols added for the new futex-based
std::call_once implementation. These symbols were new on trunk, so not
in any released version. However, they are already present in some
beta distro releases (Fedora Linux 34) and in Fedora Linux rawhide. This
change can be locally reverted by distros that need to keep the symbols
present until affected packages have been rebuilt.
libstdc++-v3/ChangeLog:
PR libstdc++/99341
* config/abi/post/aarch64-linux-gnu/baseline_symbols.txt: Remove
std::once_flag symbols.
* config/abi/post/ia64-linux-gnu/baseline_symbols.txt: Likewise.
* config/abi/post/m68k-linux-gnu/baseline_symbols.txt: Likewise.
* config/abi/post/riscv64-linux-gnu/baseline_symbols.txt:
Likewise.
* config/abi/pre/gnu.ver: Likewise.
* src/c++11/mutex.cc [_GLIBCXX_HAVE_LINUX_FUTEX]
(struct __once_flag_compat): Remove.
(_ZNSt9once_flag11_M_activateEv): Remove.
(_ZNSt9once_flag9_M_finishEb): Remove.
diff --git a/libstdc++-v3/config/abi/post/aarch64-linux-gnu/baseline_symbols.txt b/libstdc++-v3/config/abi/post/aarch64-linux-gnu/baseline_symbols.txt
index 45f1540ca11..898c8e1e895 100644
--- a/libstdc++-v3/config/abi/post/aarch64-linux-gnu/baseline_symbols.txt
+++ b/libstdc++-v3/config/abi/post/aarch64-linux-gnu/baseline_symbols.txt
@@ -4086,8 +4086,6 @@ FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEEC2Em@@GLIBCXX
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED0Ev@@GLIBCXX_3.4
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED1Ev@@GLIBCXX_3.4
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED2Ev@@GLIBCXX_3.4
-FUNC:_ZNSt9once_flag11_M_activateEv@@GLIBCXX_3.4.29
-FUNC:_ZNSt9once_flag9_M_finishEb@@GLIBCXX_3.4.29
FUNC:_ZNSt9strstream3strEv@@GLIBCXX_3.4
FUNC:_ZNSt9strstream6freezeEb@@GLIBCXX_3.4
FUNC:_ZNSt9strstreamC1EPciSt13_Ios_Openmode@@GLIBCXX_3.4
diff --git a/libstdc++-v3/config/abi/post/ia64-linux-gnu/baseline_symbols.txt b/libstdc++-v3/config/abi/post/ia64-linux-gnu/baseline_symbols.txt
index 62d28d2cd04..92288ccb8a6 100644
--- a/libstdc++-v3/config/abi/post/ia64-linux-gnu/baseline_symbols.txt
+++ b/libstdc++-v3/config/abi/post/ia64-linux-gnu/baseline_symbols.txt
@@ -4086,8 +4086,6 @@ FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEEC2Em@@GLIBCXX
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED0Ev@@GLIBCXX_3.4
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED1Ev@@GLIBCXX_3.4
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED2Ev@@GLIBCXX_3.4
-FUNC:_ZNSt9once_flag11_M_activateEv@@GLIBCXX_3.4.29
-FUNC:_ZNSt9once_flag9_M_finishEb@@GLIBCXX_3.4.29
FUNC:_ZNSt9strstream3strEv@@GLIBCXX_3.4
FUNC:_ZNSt9strstream6freezeEb@@GLIBCXX_3.4
FUNC:_ZNSt9strstreamC1EPciSt13_Ios_Openmode@@GLIBCXX_3.4
diff --git a/libstdc++-v3/config/abi/post/m68k-linux-gnu/baseline_symbols.txt b/libstdc++-v3/config/abi/post/m68k-linux-gnu/baseline_symbols.txt
index 45992aef3ec..af5dc020e00 100644
--- a/libstdc++-v3/config/abi/post/m68k-linux-gnu/baseline_symbols.txt
+++ b/libstdc++-v3/config/abi/post/m68k-linux-gnu/baseline_symbols.txt
@@ -4086,8 +4086,6 @@ FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEEC2Ej@@GLIBCXX
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED0Ev@@GLIBCXX_3.4
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED1Ev@@GLIBCXX_3.4
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED2Ev@@GLIBCXX_3.4
-FUNC:_ZNSt9once_flag11_M_activateEv@@GLIBCXX_3.4.29
-FUNC:_ZNSt9once_flag9_M_finishEb@@GLIBCXX_3.4.29
FUNC:_ZNSt9strstream3strEv@@GLIBCXX_3.4
FUNC:_ZNSt9strstream6freezeEb@@GLIBCXX_3.4
FUNC:_ZNSt9strstreamC1EPciSt13_Ios_Openmode@@GLIBCXX_3.4
diff --git a/libstdc++-v3/config/abi/post/riscv64-linux-gnu/baseline_symbols.txt b/libstdc++-v3/config/abi/post/riscv64-linux-gnu/baseline_symbols.txt
index 02a2e176bd7..6e5da521255 100644
--- a/libstdc++-v3/config/abi/post/riscv64-linux-gnu/baseline_symbols.txt
+++ b/libstdc++-v3/config/abi/post/riscv64-linux-gnu/baseline_symbols.txt
@@ -4086,8 +4086,6 @@ FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEEC2Em@@GLIBCXX
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED0Ev@@GLIBCXX_3.4
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED1Ev@@GLIBCXX_3.4
FUNC:_ZNSt9money_putIwSt19ostreambuf_iteratorIwSt11char_traitsIwEEED2Ev@@GLIBCXX_3.4
-FUNC:_ZNSt9once_flag11_M_activateEv@@GLIBCXX_3.4.29
-FUNC:_ZNSt9once_flag9_M_finishEb@@GLIBCXX_3.4.29
FUNC:_ZNSt9strstream3strEv@@GLIBCXX_3.4
FUNC:_ZNSt9strstream6freezeEb@@GLIBCXX_3.4
FUNC:_ZNSt9strstreamC1EPciSt13_Ios_Openmode@@GLIBCXX_3.4
diff --git a/libstdc++-v3/config/abi/pre/gnu.ver b/libstdc++-v3/config/abi/pre/gnu.ver
index a2c151d11ac..5323c7f0604 100644
--- a/libstdc++-v3/config/abi/pre/gnu.ver
+++ b/libstdc++-v3/config/abi/pre/gnu.ver
@@ -2388,11 +2388,6 @@ GLIBCXX_3.4.29 {
_ZNKRSt7__cxx1118basic_stringstreamI[cw]St11char_traitsI[cw]ESaI[cw]EE3strEv;
_ZNSt7__cxx1118basic_stringstreamI[cw]St11char_traitsI[cw]ESaI[cw]EE3strEONS_12basic_stringI[cw]S2_S3_EE;
- # std::once_flag::_M_activate()
- _ZNSt9once_flag11_M_activateEv;
- # std::once_flag::_M_finish(bool)
- _ZNSt9once_flag9_M_finishEb;
-
# std::to_chars(char*, char*, [float|double|long double])
_ZSt8to_charsPcS_[def];
# std::to_chars(char*, char*, [float|double|long double], chars_format)
diff --git a/libstdc++-v3/src/c++11/mutex.cc b/libstdc++-v3/src/c++11/mutex.cc
index 3b48998b7e4..646fd17ec45 100644
--- a/libstdc++-v3/src/c++11/mutex.cc
+++ b/libstdc++-v3/src/c++11/mutex.cc
@@ -26,90 +26,6 @@
#ifdef _GLIBCXX_HAS_GTHREADS
-#if defined _GLIBCXX_SHARED && ! _GLIBCXX_INLINE_VERSION
-
-#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
-# include <syscall.h>
-# include <unistd.h>
-# include <limits.h>
-
-namespace std _GLIBCXX_VISIBILITY(default)
-{
-_GLIBCXX_BEGIN_NAMESPACE_VERSION
-
-struct __once_flag_compat
-{
- enum _Bits : int { _Init = 0, _Active = 1, _Done = 2 };
- int _M_once = 0;
- bool _M_activate();
- void _M_finish(bool returning) noexcept;
-};
-
-bool
-__once_flag_compat::_M_activate()
-{
- if (__gnu_cxx::__is_single_threaded())
- {
- if (_M_once == _Bits::_Done)
- return false;
- _M_once = _Bits::_Active;
- return true;
- }
-
- while (true)
- {
- int expected = _Bits::_Init;
- constexpr int active = _Bits::_Active;
- if (__atomic_compare_exchange_n(&_M_once, &expected, active, false,
- __ATOMIC_ACQ_REL,
- __ATOMIC_ACQUIRE))
- {
- // This thread is now doing an active execution.
- return true;
- }
-
- if (expected == _Bits::_Done)
- return false; // A returning execution happened, this is passive.
-
- // Otherwise, an active execution is happening. Wait for it to finish.
- constexpr int futex_wait = 128; // FUTEX_WAIT_PRIVATE
- syscall (SYS_futex, &_M_once, futex_wait, expected, 0);
- }
-}
-
-void
-std::__once_flag_compat::_M_finish(bool returning) noexcept
-{
- const int newval = returning ? _Bits::_Done : _Bits::_Init;
- if (__gnu_cxx::__is_single_threaded())
- {
- __glibcxx_assert(_M_once == _Bits::_Active);
- _M_once = newval;
- }
- else
- {
- int prev [[maybe_unused]]
- = __atomic_exchange_n(&_M_once, newval, __ATOMIC_RELEASE);
- __glibcxx_assert(prev & _Bits::_Active);
- // Wake any other threads waiting for this execution to finish.
- constexpr int futex_wake = 129; // FUTEX_WAKE_PRIVATE
- syscall (SYS_futex, &_M_once, futex_wake, INT_MAX);
- }
-}
-
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wattribute-alias"
-extern "C" bool _ZNSt9once_flag11_M_activateEv()
- __attribute__((alias ("_ZNSt18__once_flag_compat11_M_activateEv")));
-extern "C" void _ZNSt9once_flag9_M_finishEb() noexcept
- __attribute__((alias ("_ZNSt18__once_flag_compat9_M_finishEb")));
-#pragma GCC diagnostic pop
-
-_GLIBCXX_END_NAMESPACE_VERSION
-} // namespace std
-#endif // FUTEX
-#endif // ONCE_FLAG_COMPAT && SHARED && ! INLINE_VERSION
-
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH 2/2] libstdc++: Remove symbols for new std::call_once implementation [PR 99341]
2021-03-12 17:46 ` [PATCH 2/2] libstdc++: Remove symbols for new " Jonathan Wakely
@ 2021-03-16 12:40 ` Jonathan Wakely
0 siblings, 0 replies; 3+ messages in thread
From: Jonathan Wakely @ 2021-03-16 12:40 UTC (permalink / raw)
To: libstdc++, gcc-patches
On 12/03/21 17:46 +0000, Jonathan Wakely wrote:
>This removes the new symbols added for the new futex-based
>std::call_once implementation. These symbols were new on trunk, so not
>in any released version. However, they are already present in some
>beta distro releases (Fedora Linux 34) and in Fedora Linux rawhide. This
>change can be locally reverted by distros that need to keep the symbols
>present until affected packages have been rebuilt.
>
>libstdc++-v3/ChangeLog:
>
> PR libstdc++/99341
> * config/abi/post/aarch64-linux-gnu/baseline_symbols.txt: Remove
> std::once_flag symbols.
> * config/abi/post/ia64-linux-gnu/baseline_symbols.txt: Likewise.
> * config/abi/post/m68k-linux-gnu/baseline_symbols.txt: Likewise.
> * config/abi/post/riscv64-linux-gnu/baseline_symbols.txt:
> Likewise.
> * config/abi/pre/gnu.ver: Likewise.
> * src/c++11/mutex.cc [_GLIBCXX_HAVE_LINUX_FUTEX]
> (struct __once_flag_compat): Remove.
> (_ZNSt9once_flag11_M_activateEv): Remove.
> (_ZNSt9once_flag9_M_finishEb): Remove.
>
>Tested x86_64-linux, powerpc64-linux and powerpc64le-linux, but not yet
>committed (it's not really appropriate for a last-minute Friday
>change!)
I've now pushed [PATCH 1/2] and this one.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-03-16 12:40 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
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2021-03-12 17:45 [PATCH 1/2] libstdc++: Revert to old std::call_once implementation [PR 99341] Jonathan Wakely
2021-03-12 17:46 ` [PATCH 2/2] libstdc++: Remove symbols for new " Jonathan Wakely
2021-03-16 12:40 ` Jonathan Wakely
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