Optimize Memory::ReadString

This function is responsible for majority of CPU time in prefetto.

Reduce the number of memory reads (don't read strings byte-by-byte).

Update all calls of ReadString to include the third parameter to have
a max read.

Add an Elf creation benchmark since this function is on the elf
creation path.

Test: libunwindstack_unit_test
Change-Id: Ia36e1f1a5ba76c9e9f13c43fb9e3691dde7897f2
diff --git a/libunwindstack/benchmarks/ElfBenchmark.cpp b/libunwindstack/benchmarks/ElfBenchmark.cpp
new file mode 100644
index 0000000..c108a2a
--- /dev/null
+++ b/libunwindstack/benchmarks/ElfBenchmark.cpp
@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include <err.h>
+#include <malloc.h>
+#include <stdint.h>
+
+#include <string>
+
+#include <benchmark/benchmark.h>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/Memory.h>
+
+#include "Utils.h"
+
+static void BenchmarkElfCreate(benchmark::State& state, const std::string& elf_file) {
+#if defined(__BIONIC__)
+  uint64_t rss_bytes = 0;
+#endif
+  uint64_t alloc_bytes = 0;
+  for (auto _ : state) {
+    state.PauseTiming();
+#if defined(__BIONIC__)
+    mallopt(M_PURGE, 0);
+    uint64_t rss_bytes_before = 0;
+    GatherRss(&rss_bytes_before);
+#endif
+    uint64_t alloc_bytes_before = mallinfo().uordblks;
+    auto file_memory = unwindstack::Memory::CreateFileMemory(elf_file, 0);
+    state.ResumeTiming();
+
+    unwindstack::Elf elf(file_memory.release());
+    if (!elf.Init() || !elf.valid()) {
+      errx(1, "Internal Error: Cannot open elf.");
+    }
+
+    state.PauseTiming();
+#if defined(__BIONIC__)
+    mallopt(M_PURGE, 0);
+#endif
+    alloc_bytes += mallinfo().uordblks - alloc_bytes_before;
+#if defined(__BIONIC__)
+    GatherRss(&rss_bytes);
+    rss_bytes -= rss_bytes_before;
+#endif
+    state.ResumeTiming();
+  }
+
+#if defined(__BIONIC__)
+  state.counters["RSS_BYTES"] = rss_bytes / static_cast<double>(state.iterations());
+#endif
+  state.counters["ALLOCATED_BYTES"] = alloc_bytes / static_cast<double>(state.iterations());
+}
+
+void BM_elf_create(benchmark::State& state) {
+  BenchmarkElfCreate(state, GetElfFile());
+}
+BENCHMARK(BM_elf_create);
+
+void BM_elf_create_compressed(benchmark::State& state) {
+  BenchmarkElfCreate(state, GetCompressedElfFile());
+}
+BENCHMARK(BM_elf_create_compressed);
diff --git a/libunwindstack/benchmarks/SymbolBenchmark.cpp b/libunwindstack/benchmarks/SymbolBenchmark.cpp
index a850ff0..73088da 100644
--- a/libunwindstack/benchmarks/SymbolBenchmark.cpp
+++ b/libunwindstack/benchmarks/SymbolBenchmark.cpp
@@ -22,33 +22,12 @@
 #include <string>
 #include <vector>
 
-#include <android-base/file.h>
-#include <android-base/strings.h>
 #include <benchmark/benchmark.h>
 
 #include <unwindstack/Elf.h>
 #include <unwindstack/Memory.h>
 
-#if defined(__BIONIC__)
-
-#include <meminfo/procmeminfo.h>
-#include <procinfo/process_map.h>
-
-static void Gather(uint64_t* rss_bytes) {
-  android::meminfo::ProcMemInfo proc_mem(getpid());
-  const std::vector<android::meminfo::Vma>& maps = proc_mem.MapsWithoutUsageStats();
-  for (auto& vma : maps) {
-    if (vma.name == "[anon:libc_malloc]" || android::base::StartsWith(vma.name, "[anon:scudo:") ||
-        android::base::StartsWith(vma.name, "[anon:GWP-ASan")) {
-      android::meminfo::Vma update_vma(vma);
-      if (!proc_mem.FillInVmaStats(update_vma)) {
-        err(1, "FillInVmaStats failed\n");
-      }
-      *rss_bytes += update_vma.usage.rss;
-    }
-  }
-}
-#endif
+#include "Utils.h"
 
 static void BenchmarkSymbolLookup(benchmark::State& state, std::vector<uint64_t> offsets,
                                   std::string elf_file, bool expect_found) {
@@ -66,7 +45,7 @@
 #if defined(__BIONIC__)
     mallopt(M_PURGE, 0);
     uint64_t rss_bytes_before = 0;
-    Gather(&rss_bytes_before);
+    GatherRss(&rss_bytes_before);
 #endif
     uint64_t alloc_bytes_before = mallinfo().uordblks;
     state.ResumeTiming();
@@ -88,7 +67,7 @@
 #endif
     alloc_bytes += mallinfo().uordblks - alloc_bytes_before;
 #if defined(__BIONIC__)
-    Gather(&rss_bytes);
+    GatherRss(&rss_bytes);
     rss_bytes -= rss_bytes_before;
 #endif
     state.ResumeTiming();
@@ -105,14 +84,6 @@
   BenchmarkSymbolLookup(state, std::vector<uint64_t>{pc}, elf_file, expect_found);
 }
 
-std::string GetElfFile() {
-  return android::base::GetExecutableDirectory() + "/benchmarks/files/libart_arm.so";
-}
-
-std::string GetSortedElfFile() {
-  return android::base::GetExecutableDirectory() + "/benchmarks/files/boot_arm.oat";
-}
-
 void BM_symbol_not_present(benchmark::State& state) {
   BenchmarkSymbolLookup(state, 0, GetElfFile(), false);
 }
@@ -136,23 +107,23 @@
 BENCHMARK(BM_symbol_find_multiple);
 
 void BM_symbol_not_present_from_sorted(benchmark::State& state) {
-  BenchmarkSymbolLookup(state, 0, GetSortedElfFile(), false);
+  BenchmarkSymbolLookup(state, 0, GetSymbolSortedElfFile(), false);
 }
 BENCHMARK(BM_symbol_not_present_from_sorted);
 
 void BM_symbol_find_single_from_sorted(benchmark::State& state) {
-  BenchmarkSymbolLookup(state, 0x138638, GetSortedElfFile(), true);
+  BenchmarkSymbolLookup(state, 0x138638, GetSymbolSortedElfFile(), true);
 }
 BENCHMARK(BM_symbol_find_single_from_sorted);
 
 void BM_symbol_find_single_many_times_from_sorted(benchmark::State& state) {
-  BenchmarkSymbolLookup(state, std::vector<uint64_t>(15, 0x138638), GetSortedElfFile(), true);
+  BenchmarkSymbolLookup(state, std::vector<uint64_t>(15, 0x138638), GetSymbolSortedElfFile(), true);
 }
 BENCHMARK(BM_symbol_find_single_many_times_from_sorted);
 
 void BM_symbol_find_multiple_from_sorted(benchmark::State& state) {
   BenchmarkSymbolLookup(state,
                         std::vector<uint64_t>{0x138638, 0x84350, 0x14df18, 0x1f3a38, 0x1f3ca8},
-                        GetSortedElfFile(), true);
+                        GetSymbolSortedElfFile(), true);
 }
 BENCHMARK(BM_symbol_find_multiple_from_sorted);
diff --git a/libunwindstack/benchmarks/Utils.cpp b/libunwindstack/benchmarks/Utils.cpp
new file mode 100644
index 0000000..c92f109
--- /dev/null
+++ b/libunwindstack/benchmarks/Utils.cpp
@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include <err.h>
+#include <stdint.h>
+
+#include <string>
+#include <vector>
+
+#include <android-base/file.h>
+#include <android-base/strings.h>
+#include <benchmark/benchmark.h>
+
+#include <unwindstack/Elf.h>
+#include <unwindstack/Memory.h>
+
+std::string GetElfFile() {
+  return android::base::GetExecutableDirectory() + "/benchmarks/files/libart_arm.so";
+}
+
+std::string GetSymbolSortedElfFile() {
+  return android::base::GetExecutableDirectory() + "/benchmarks/files/boot_arm.oat";
+}
+
+std::string GetCompressedElfFile() {
+  // Both are the same right now.
+  return GetSymbolSortedElfFile();
+}
+
+#if defined(__BIONIC__)
+
+#include <meminfo/procmeminfo.h>
+#include <procinfo/process_map.h>
+
+void GatherRss(uint64_t* rss_bytes) {
+  android::meminfo::ProcMemInfo proc_mem(getpid());
+  const std::vector<android::meminfo::Vma>& maps = proc_mem.MapsWithoutUsageStats();
+  for (auto& vma : maps) {
+    if (vma.name == "[anon:libc_malloc]" || android::base::StartsWith(vma.name, "[anon:scudo:") ||
+        android::base::StartsWith(vma.name, "[anon:GWP-ASan")) {
+      android::meminfo::Vma update_vma(vma);
+      if (!proc_mem.FillInVmaStats(update_vma)) {
+        err(1, "FillInVmaStats failed\n");
+      }
+      *rss_bytes += update_vma.usage.rss;
+    }
+  }
+}
+#endif
diff --git a/libunwindstack/benchmarks/Utils.h b/libunwindstack/benchmarks/Utils.h
new file mode 100644
index 0000000..bee6efc
--- /dev/null
+++ b/libunwindstack/benchmarks/Utils.h
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#ifndef _LIBUNWINDSTACK_UTILS_H
+#define _LIBUNWINDSTACK_UTILS_H
+
+#include <stdint.h>
+
+#include <string>
+
+std::string GetElfFile();
+
+std::string GetSymbolSortedElfFile();
+
+std::string GetCompressedElfFile();
+
+#if defined(__BIONIC__)
+
+#include <meminfo/procmeminfo.h>
+#include <procinfo/process_map.h>
+
+void GatherRss(uint64_t* rss_bytes);
+
+#endif
+
+#endif  // _LIBUNWINDSTACK_UTILS_h