Hi!
The sys_futex0 caller expects return values as returned by raw syscalls,
i.e. value >= 0 success, negative value are errors -errorval.
But, the syscall function returns value >= 0 on success, and -1 on error,
with errno set to errorval. This means if e.g. futex syscall fails with
EAGAIN, and EPERM is 1, we get GTM program terminated because we think
futex returned -EPERM.
Fixed thusly, bootstrapped/regtested on s390x-linux, ok for trunk/4.8?
Testcase that previously succeeded at most 9 times in a row before crashing
now succeeded over 38000 iterations in a row (before I've stopped it).
2014-03-26 Jakub Jelinek <ja...@redhat.com>
* config/linux/futex_bits.h: Include errno.h.
(sys_futex0): If syscall returns -1, return -errno rather than
-1.
--- libitm/config/linux/futex_bits.h 2014-01-03 11:41:27.495153749 +0100
+++ libitm/config/linux/futex_bits.h 2014-03-26 18:03:15.307302524 +0100
@@ -31,9 +31,13 @@
#include <unistd.h>
#include <sys/syscall.h>
+#include <errno.h>
static inline long
sys_futex0 (std::atomic<int> *addr, long op, long val)
{
- return syscall (SYS_futex, (int*) addr, op, val, 0);
+ long res = syscall (SYS_futex, (int*) addr, op, val, 0);
+ if (__builtin_expect (res == -1, 0))
+ return -errno;
+ return res;
}
Jakub
