Ensure that the test version of the command line tool is stable for benchmarking (#2076)

Some benchmark suites contain test cases that have nonreproducible
behaviour. This is mostly caused by relying on "now" when dealing
with dates or timestamps, instead of using a fixed moment. (A
notorious example is the crypto-aes.js test case of the sunspider
bechmark suite, where the heap memory consumption can vary between
34K-41K heap because of using `(new Date()).getTime()`.)

This commit renames the jerry-minimal command line tool to
jerry-test (to better reflect its purpose) and adds extra code,
which intercepts some calls to libc (`gettimeofday`, `rand`) and
pins their results to some fixed values. This makes the tool
useless in a general case but ensures stable results when
benchmarking -- for which it is mostly used.

As a side effect, the commit also changes jerry-libc by making all
libc functions weak symbols to allow their override from
application code.

JerryScript-DCO-1.0-Signed-off-by: Akos Kiss akiss@inf.u-szeged.hu

jerry-main/benchmarking.c

@@ -0,0 +1,63 @@
+/* Copyright JS Foundation and other contributors, http://js.foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * This source contains libc overrides for the sake of stable benchmarking. If
+ * building a binary for the purpose of benchmarking, the object compiled from
+ * this source is to be injected into the list of objects-to-be-linked before
+ * the list of libraries-to-be-linked to ensure that the linker picks up these
+ * implementations.
+ */
+
+ #ifdef __GNUC__
+/*
+ * Note:
+ *      This is nasty and dangerous. However, we only need the timeval structure
+ *      from sys/time.h. Unfortunately, the same header also declares
+ *      gettimeofday, which has different declarations on different platforms
+ *      (e.g., macOS, Linux). So, instead of #ifdef'ing for platforms, we simply
+ *      tweak the header to declare another function. Don't try this at home.
+ */
+#define gettimeofday __prevent_conflicting_gettimeofday_declarations__
+#include <sys/time.h>
+#undef gettimeofday
+
+int gettimeofday (struct timeval *, void *);
+
+/**
+ * Useless but stable gettimeofday implementation. Returns Epoch. Ensures that
+ * test cases relying on "now" yield stable results.
+ */
+int gettimeofday (struct timeval *tv,
+                  void *tz)
+{
+  (void) tz;
+  tv->tv_sec = 0;
+  tv->tv_usec = 0;
+  return 0;
+} /* gettimeofday */
+#endif /* __GNUC__ */
+
+
+int rand (void);
+
+/**
+ * Useless but stable rand implementation. Returns 4. Ensures that test cases
+ * relying on randomness yield stable results.
+ */
+int rand (void)
+{
+  return 4; /* Chosen by fair dice roll. Guaranteed to be random. */
+} /* rand */