linux-user: fix target_to_host_timespec64()

in 32 bit mode, drop the padding in tv_nsec. If host is 64bit and target
is 32bit, the padding bytes will be copied from the target and as the
kernel checks the value, the syscall exits with EINVAL.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20200827070449.2386007-1-laurent@vivier.eu>
Fixes: c6c8d10 ("linux-user/syscall: Add support for clock_gettime64/clock_settime64")

linux-user/syscall.c

@@ -1229,6 +1229,8 @@ static inline abi_long target_to_host_timespec64(struct timespec *host_ts,
     }
     __get_user(host_ts->tv_sec, &target_ts->tv_sec);
     __get_user(host_ts->tv_nsec, &target_ts->tv_nsec);
+    /* in 32bit mode, this drops the padding */
+    host_ts->tv_nsec = (long)(abi_long)host_ts->tv_nsec;
     unlock_user_struct(target_ts, target_addr, 0);
     return 0;
 }