Index: qemu/linux-user/syscall.c
===================================================================
--- qemu.orig/linux-user/syscall.c	2007-11-28 17:26:46.000000000 -0700
+++ qemu/linux-user/syscall.c	2007-11-28 17:29:11.000000000 -0700
@@ -3398,10 +3398,14 @@
         ret = 0; /* avoid warning */
         break;
     case TARGET_NR_read:
-        if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
-            goto efault;
-        ret = get_errno(read(arg1, p, arg3));
-        unlock_user(p, arg2, ret);
+        if (!arg3)
+            ret = 0;
+        else {
+            if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
+                goto efault;
+            ret = get_errno(read(arg1, p, arg3));
+            unlock_user(p, arg2, ret);
+        }
         break;
     case TARGET_NR_write:
         if (!(p = lock_user(VERIFY_READ, arg2, arg3, 1)))