Add a linker relocation benchmark

The benchmark creates a set of DSOs that mimic the work involved in
loading the current version of libandroid_servers.so. The synthetic
benchmark has roughly the same number of libraries with roughly the same
relocations.

Currently, on a local aosp_walleye build that includes recent performance
improvements (including the Neon-based CL
I3983bca1dddc9241bb70290ad3651d895f046660), using the "performance"
governor, the benchmark reports these scores:

$ adb shell taskset 10 \
  /data/benchmarktest64/linker-reloc-bench/linker-reloc-bench \
  --benchmark_repetitions=20 --benchmark_display_aggregates_only=true
...
--------------------------------------------------------------------------------
Benchmark                                      Time             CPU   Iterations
--------------------------------------------------------------------------------
BM_linker_relocation/real_time_mean        70048 us          465 us           20
BM_linker_relocation/real_time_median      70091 us          466 us           20
BM_linker_relocation/real_time_stddev        329 us         8.29 us           20

$ adb shell taskset 10 \
  /data/benchmarktest/linker-reloc-bench/linker-reloc-bench \
  --benchmark_repetitions=20 --benchmark_display_aggregates_only=true
...
--------------------------------------------------------------------------------
Benchmark                                      Time             CPU   Iterations
--------------------------------------------------------------------------------
BM_linker_relocation/real_time_mean        83051 us          462 us           20
BM_linker_relocation/real_time_median      83069 us          464 us           20
BM_linker_relocation/real_time_stddev        184 us         8.91 us           20

Test: manual
Bug: none
Change-Id: I6dac66978f8666f95c76387093bda6be0151bfce
diff --git a/benchmarks/linker_relocation/linker_reloc_bench.cpp b/benchmarks/linker_relocation/linker_reloc_bench.cpp
new file mode 100644
index 0000000..c8a64e1
--- /dev/null
+++ b/benchmarks/linker_relocation/linker_reloc_bench.cpp
@@ -0,0 +1,57 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdlib.h>
+
+#include "spawn_benchmark.h"
+
+#if defined(__LP64__)
+static constexpr const char* kNativeTestDir = "nativetest64";
+#else
+static constexpr const char* kNativeTestDir = "nativetest";
+#endif
+
+static void BM_linker_relocation(benchmark::State& state) {
+  std::string main = test_program("linker_reloc_bench_main");
+
+  // Translate from:
+  //    /data/benchmarktest[64]/linker-reloc-bench    [exe dir]
+  // to:
+  //    /data/nativetest[64]/linker-reloc-bench       [dir with test libs]
+  std::string test_lib_dir = 
+      android::base::Dirname(android::base::Dirname(android::base::GetExecutableDirectory())) +
+      "/" + kNativeTestDir + "/linker-reloc-bench";
+
+  setenv("LD_LIBRARY_PATH", test_lib_dir.c_str(), 1);
+
+  BM_spawn_test(state, (const char*[]) { main.c_str(), nullptr });
+}
+
+BENCHMARK(BM_linker_relocation)->UseRealTime()->Unit(benchmark::kMicrosecond);
+
+BENCHMARK_MAIN();