--- a/js/src/devtools/rootAnalysis/utility.js
+++ b/js/src/devtools/rootAnalysis/utility.js
@@ -153,26 +153,26 @@ function cLibrary()
     } catch(e) {
         lib = ctypes.open("libc.so");
     }
 
     return {
         fopen: lib.declare("fopen", ctypes.default_abi, ctypes.void_t.ptr, ctypes.char.ptr, ctypes.char.ptr),
         getline: lib.declare("getline", ctypes.default_abi, ctypes.ssize_t, ctypes.char.ptr.ptr, ctypes.size_t.ptr, ctypes.void_t.ptr),
         fclose: lib.declare("fopen", ctypes.default_abi, ctypes.int, ctypes.void_t.ptr),
-        free: lib.declare("free", ctypes.default_abi, ctypes.void_t.ptr),
+        setvbuf: lib.declare("setvbuf", ctypes.default_abi, ctypes.int, ctypes.void_t.ptr, ctypes.char.ptr, ctypes.int, ctypes.size_t),
     };
 }
 
 function* readFileLines_gen(filename)
 {
-    var libc = cLibrary();
-    var linebuf = ctypes.char.ptr();
-    var bufsize = ctypes.size_t(0);
-    var fp = libc.fopen(filename, "r");
-    if (fp.isNull())
-        throw "Unable to open '" + filename + "'"
+  var libc = cLibrary();
+  var linebuf = ctypes.char.array(4096)();
+  var bufsize = ctypes.size_t(4096);
+  var fp = libc.fopen(filename, "r");
+  if (fp.isNull())
+    throw "Unable to open '" + filename + "'"
 
-    while (libc.getline(linebuf.address(), bufsize.address(), fp) > 0)
-        yield linebuf.readString();
-    libc.fclose(fp);
-    libc.free(ctypes.void_t.ptr(linebuf));
+  var bufp = ctypes.char.ptr(linebuf.addressOfElement(0));
+  while (libc.getline(bufp.address(), bufsize.address(), fp) > 0)
+    yield bufp.readString();
+  libc.fclose(fp);
 }