https://bugs.kde.org/show_bug.cgi?id=359201
Bug ID: 359201
Summary: futex syscall "skips" argument 5 if op is
FUTEXT_WAIT_BITSET
Product: valgrind
Version: 3.11 SVN
Platform: Other
URL: https://bugzilla.redhat.com/show_bug.cgi?id=1305962
OS: Linux
Status: UNCONFIRMED
Severity: normal
Priority: NOR
Component: general
Assignee: jsew...@acm.org
Reporter: m...@redhat.com
The following program:
#include <chrono>
#include <condition_variable>
#include <mutex>
#include <thread>
using namespace std;
mutex m;
timed_mutex tmx;
condition_variable cv;
bool ready = false;
bool finished = false;
bool IsReady()
{
return ready;
}
bool IsFinished()
{
return finished;
}
void worker()
{
// Wait until main thread tells us we can proceed
unique_lock< mutex > lk( m );
cv.wait_for( lk, chrono::seconds( 10 ), &IsReady );
unique_lock< timed_mutex > lock( tmx, chrono::milliseconds( 1 ) );
finished = true;
lk.unlock();
cv.notify_one();
}
int main()
{
unique_lock< timed_mutex > lock( tmx );
thread workerThread( &worker );
// tell worker() to proceed
{
unique_lock< mutex > lk( m );
ready = true;
}
cv.notify_one();
{
// wait for the worker()
unique_lock< mutex > lk( m );
cv.wait_for( lk, chrono::milliseconds( 100 ), &IsFinished );
}
workerThread.join();
return 0;
}
Compiled with g++ 4.8.5 and using glibc-2.17-106 on x86_64 (newer versions
don't exhibit the issue) g++ -std=c++11 -pthread -g -O0 -o mutex.bin test.cpp
will produce:
==5930== Syscall param futex(dummy) contains uninitialised byte(s)
==5930== at 0x5663F8C: __lll_timedlock_wait (lowlevellock.S:190)
==5930== by 0x5660A97: _L_timedlock_67 (pthread_mutex_timedlock.c:236)
==5930== by 0x566032B: pthread_mutex_timedlock
(pthread_mutex_timedlock.c:83)
==5930== by 0x401108: __gthread_mutex_timedlock(pthread_mutex_t*, timespec
const*) (gthr-default.h:768)
==5930== by 0x4029A7: bool
std::timed_mutex::_M_try_lock_until<std::chrono::duration<long, std::ratio<1l,
1000000000l> > >(std::chrono::time_point<std::chrono::_V2::steady_clock,
std::chrono::duration<long, std::ratio<1l, 1000000000l> > > const&) (mutex:286)
==5930== by 0x4023DE: bool std::timed_mutex::_M_try_lock_for<long,
std::ratio<1l, 1000l> >(std::chrono::duration<long, std::ratio<1l, 1000l> >
const&) (mutex:267)
==5930== by 0x401FBE: bool std::timed_mutex::try_lock_for<long,
std::ratio<1l, 1000l> >(std::chrono::duration<long, std::ratio<1l, 1000l> >
const&) (mutex:240)
==5930== by 0x401AFC: std::unique_lock<std::timed_mutex>::unique_lock<long,
std::ratio<1l, 1000l> >(std::timed_mutex&, std::chrono::duration<long,
std::ratio<1l, 1000l> > const&) (mutex:470)
==5930== by 0x40128B: worker() (test.cpp:30)
==5930== by 0x403504: void std::_Bind_simple<void
(*())()>::_M_invoke<>(std::_Index_tuple<>) (functional:1732)
==5930== by 0x40345E: std::_Bind_simple<void (*())()>::operator()()
(functional:1720)
==5930== by 0x4033F7: std::thread::_Impl<std::_Bind_simple<void (*())()>
>::_M_run() (thread:115)
Reproducible: Always
What seems to happen is that argument 5 (uaddr2 aka dummy) really is not used.
That is also what the futex manpage says for FUTEX_WAIT_BITSET says.
http://man7.org/linux/man-pages/man2/futex.2.html
But for some reason in this particular case we call futex FUTEXT_WAIT_BITSET
with that argument register really containing some uninitialized stuff and get
a warning. We really should not check argument 5, but we should check argument
6.
Proposed patch, that fixes the issue for me:
diff --git a/coregrind/m_syswrap/syswrap-linux.c
b/coregrind/m_syswrap/syswrap-linux.c
index f796969..b57436c 100644
--- a/coregrind/m_syswrap/syswrap-linux.c
+++ b/coregrind/m_syswrap/syswrap-linux.c
@@ -1154,13 +1154,16 @@ PRE(sys_futex)
return;
}
if (*(vki_u32 *)ARG1 != ARG3) {
- PRE_REG_READ5(long, "futex",
+ PRE_REG_READ4(long, "futex",
vki_u32 *, futex, int, op, int, val,
- struct timespec *, utime, int, dummy);
+ struct timespec *, utime);
} else {
- PRE_REG_READ6(long, "futex",
+ /* Note argument 5 is unused, but argument 6 is used.
+ So we cannot just PRE_REG_READ6. Read argument 6 separately. */
+ PRE_REG_READ4(long, "futex",
vki_u32 *, futex, int, op, int, val,
- struct timespec *, utime, int, dummy, int, val3);
+ struct timespec *, utime);
+ PRA6("futex",int,val3);
}
break;
case VKI_FUTEX_WAKE_BITSET:
--
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