3 files changed, 70 insertions, 1 deletions

diff --git a/src/kern/linux/linux.hh b/src/kern/linux/linux.hh
index 2da596814..4ed39028b 100644
--- a/src/kern/linux/linux.hh
+++ b/src/kern/linux/linux.hh
@@ -241,6 +241,8 @@ class Linux : public OperatingSystem
     // For futex system call
     static const unsigned TGT_FUTEX_WAIT                = 0;
     static const unsigned TGT_FUTEX_WAKE                = 1;
+    static const unsigned TGT_FUTEX_REQUEUE             = 3;
+    static const unsigned TGT_FUTEX_CMP_REQUEUE         = 4;
     static const unsigned TGT_FUTEX_WAIT_BITSET         = 9;
     static const unsigned TGT_FUTEX_WAKE_BITSET         = 10;
     static const unsigned TGT_EAGAIN                    = 11;
diff --git a/src/sim/futex_map.hh b/src/sim/futex_map.hh
index 6f1f7a2a1..3d34109be 100644
--- a/src/sim/futex_map.hh
+++ b/src/sim/futex_map.hh
@@ -221,6 +221,60 @@ class FutexMap : public std::unordered_map<FutexKey, WaiterList>
 
         return woken_up;
     }
+
+    /**
+     * This operation wakes a given number (val) of waiters. If there are
+     * more threads waiting than woken, they are removed from the wait
+     * queue of the futex pointed to by addr1 and added to the wait queue
+     * of the futex pointed to by addr2. The number of waiter moved is
+     * capped by count2 (misused timeout parameter).
+     *
+     * The return value is the number of waiters that are woken or
+     * requeued.
+     */
+    int
+    requeue(Addr addr1, uint64_t tgid, int count, int count2, Addr addr2)
+    {
+        FutexKey key1(addr1, tgid);
+        auto it1 = find(key1);
+
+        if (it1 == end())
+            return 0;
+
+        int woken_up = 0;
+        auto &waiterList1 = it1->second;
+
+        while (!waiterList1.empty() && woken_up < count) {
+            waiterList1.front().tc->activate();
+            waiterList1.pop_front();
+            woken_up++;
+        }
+
+        WaiterList tmpList;
+        int requeued = 0;
+
+        while (!waiterList1.empty() && requeued < count2) {
+          auto w = waiterList1.front();
+          waiterList1.pop_front();
+          tmpList.push_back(w);
+          requeued++;
+        }
+
+        FutexKey key2(addr2, tgid);
+        auto it2 = find(key2);
+
+        if (it2 == end() && requeued > 0) {
+            insert({key2, tmpList});
+        } else {
+            it2->second.insert(it2->second.end(),
+                               tmpList.begin(), tmpList.end());
+        }
+
+        if (waiterList1.empty())
+            erase(it1);
+
+        return woken_up + requeued;
+    }
 };
 
 #endif // __FUTEX_MAP_HH__
diff --git a/src/sim/syscall_emul.hh b/src/sim/syscall_emul.hh
index 295598c52..0b7585cb4 100644
--- a/src/sim/syscall_emul.hh
+++ b/src/sim/syscall_emul.hh
@@ -441,8 +441,21 @@ futexFunc(SyscallDesc *desc, int callnum, Process *process,
         return futex_map.wakeup(uaddr, process->tgid(), val);
     } else if (OS::TGT_FUTEX_WAKE_BITSET == op) {
         return futex_map.wakeup_bitset(uaddr, process->tgid(), val3);
-    }
+    } else if (OS::TGT_FUTEX_REQUEUE == op ||
+               OS::TGT_FUTEX_CMP_REQUEUE == op) {
 
+        // Ensure futex system call accessed atomically.
+        BufferArg buf(uaddr, sizeof(int));
+        buf.copyIn(tc->getMemProxy());
+        int mem_val = *(int*)buf.bufferPtr();
+        /*
+         * For CMP_REQUEUE, the whole operation is only started only if
+         * val3 is still the value of the futex pointed to by uaddr.
+         */
+        if (OS::TGT_FUTEX_CMP_REQUEUE && val3 != mem_val)
+            return -OS::TGT_EWOULDBLOCK;
+        return futex_map.requeue(uaddr, process->tgid(), val, timeout, uaddr2);
+    }
     warn("futex: op %d not implemented; ignoring.", op);
     return -ENOSYS;
 }