https://gcc.gnu.org/g:a7c5c4931f50b9898409d0101fad47abc9a223c3
commit r14-11160-ga7c5c4931f50b9898409d0101fad47abc9a223c3
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Tue Dec 17 21:32:19 2024 +0000
libstdc++: Fix std::future::wait_until for subsecond negative times
[PR118093]
The current check for negative times (i.e. before the epoch) only checks
for a negative number of seconds. For a time 1ms before the epoch the
seconds part will be zero, but the futex syscall will still fail with an
EINVAL error. Extend the check to handle this case.
This change adds a redundant check in the headers too, so that we avoid
even calling into the library for negative times. Both checks can be
marked [[unlikely]]. The check in the headers avoids the cost of
splitting the time into seconds and nanoseconds and then making a PLT
call. The check inside the library matches where we were checking
already, and fixes existing binaries that were compiled against older
headers but use a newer libstdc++.so.6 at runtime.
libstdc++-v3/ChangeLog:
PR libstdc++/118093
* include/bits/atomic_futex.h (_M_load_and_test_until_impl):
Return false for times before the epoch.
* src/c++11/futex.cc (_M_futex_wait_until): Extend check for
negative times to check for subsecond times. Add unlikely
attribute.
(_M_futex_wait_until_steady): Likewise.
* testsuite/30_threads/future/members/118093.cc: New test.
(cherry picked from commit 8ade3c3ea77e166f2873fb7ae57f9690e2b8d0e0)
Diff:
---
libstdc++-v3/include/bits/atomic_futex.h | 20 ++++++++++-------
libstdc++-v3/src/c++11/futex.cc | 4 ++--
.../testsuite/30_threads/future/members/118093.cc | 26 ++++++++++++++++++++++
3 files changed, 40 insertions(+), 10 deletions(-)
diff --git a/libstdc++-v3/include/bits/atomic_futex.h
b/libstdc++-v3/include/bits/atomic_futex.h
index dd6541748739..390c3e500ded 100644
--- a/libstdc++-v3/include/bits/atomic_futex.h
+++ b/libstdc++-v3/include/bits/atomic_futex.h
@@ -170,11 +170,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bool __equal, memory_order __mo,
const chrono::time_point<std::chrono::system_clock, _Dur>& __atime)
{
- auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
- auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
- // XXX correct?
+ auto __d = __atime.time_since_epoch();
+ if (__d < __d.zero()) [[__unlikely__]]
+ return false;
+ auto __s = chrono::duration_cast<chrono::seconds>(__d);
+ auto __ns = chrono::duration_cast<chrono::nanoseconds>(__d - __s);
return _M_load_and_test_until(__assumed, __operand, __equal, __mo,
- true, __s.time_since_epoch(), __ns);
+ true, __s, __ns);
}
template<typename _Dur>
@@ -183,11 +185,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bool __equal, memory_order __mo,
const chrono::time_point<std::chrono::steady_clock, _Dur>& __atime)
{
- auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
- auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
- // XXX correct?
+ auto __d = __atime.time_since_epoch();
+ if (__d < __d.zero()) [[__unlikely__]]
+ return false;
+ auto __s = chrono::duration_cast<chrono::seconds>(__d);
+ auto __ns = chrono::duration_cast<chrono::nanoseconds>(__d - __s);
return _M_load_and_test_until_steady(__assumed, __operand, __equal, __mo,
- true, __s.time_since_epoch(), __ns);
+ true, __s, __ns);
}
public:
diff --git a/libstdc++-v3/src/c++11/futex.cc b/libstdc++-v3/src/c++11/futex.cc
index ada2fdf3c417..6139fc354c61 100644
--- a/libstdc++-v3/src/c++11/futex.cc
+++ b/libstdc++-v3/src/c++11/futex.cc
@@ -128,7 +128,7 @@ namespace
if (!futex_clock_realtime_unavailable.load(std::memory_order_relaxed))
{
// futex sets errno=EINVAL for absolute timeouts before the epoch.
- if (__s.count() < 0)
+ if (__s.count() < 0 || __ns.count() < 0) [[unlikely]]
return false;
syscall_timespec rt;
@@ -204,7 +204,7 @@ namespace
if (!futex_clock_monotonic_unavailable.load(std::memory_order_relaxed))
{
// futex sets errno=EINVAL for absolute timeouts before the epoch.
- if (__s.count() < 0) [[unlikely]]
+ if (__s.count() < 0 || __ns.count() < 0) [[unlikely]]
return false;
syscall_timespec rt;
diff --git a/libstdc++-v3/testsuite/30_threads/future/members/118093.cc
b/libstdc++-v3/testsuite/30_threads/future/members/118093.cc
new file mode 100644
index 000000000000..2bb1e1c6dadc
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/future/members/118093.cc
@@ -0,0 +1,26 @@
+// { dg-do run { target c++11 } }
+
+#include <chrono>
+#include <future>
+
+void
+test_sys()
+{
+ std::promise<void> p;
+ std::chrono::system_clock::time_point tp(std::chrono::milliseconds{-10});
+ (void) p.get_future().wait_until(tp);
+}
+
+void
+test_steady()
+{
+ std::promise<void> p;
+ std::chrono::steady_clock::time_point tp(std::chrono::milliseconds{-10});
+ (void) p.get_future().wait_until(tp);
+}
+
+int main()
+{
+ test_sys();
+ test_steady();
+}
