Add method to detect remote read function to use.
The process_vm_read function is much faster than ptrace, but sometimes
that will not work on a remote process. Modify the libunwindstack
MemoryRemote object to figure out which one it can use.
Wrote new unit test to verify this checking behavior.
Modify libbacktrace so that the read from libunwind is used instead of
using the default ptrace calls.
Add some benchmarks to libbacktrace to compare the two different methods.
Test: Ran unit tests libbacktrace/libunwindstack/debuggerd.
Test: Ran debuggerd -b <SYSTEM_SERVER_PID>
Test: Ran debuggerd -b <MEDIACODEC PID>
Test: Ran debuggerd -b <RANDOM_PID>
Test: Used crasher to create tombstones and verified stack data is
Test: dumped properly.
Change-Id: If75ca238289532dd8e1de430d569cabb2523380a
diff --git a/libbacktrace/backtrace_read_benchmarks.cpp b/libbacktrace/backtrace_read_benchmarks.cpp
new file mode 100644
index 0000000..6a688b0
--- /dev/null
+++ b/libbacktrace/backtrace_read_benchmarks.cpp
@@ -0,0 +1,197 @@
+/*
+ * Copyright (C) 2017 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 <errno.h>
+#include <signal.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/ptrace.h>
+#include <sys/types.h>
+#include <sys/uio.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <memory>
+#include <vector>
+
+#include <benchmark/benchmark.h>
+
+#include <backtrace/Backtrace.h>
+
+#define AT_COMMON_SIZES Arg(1)->Arg(4)->Arg(8)->Arg(16)->Arg(100)->Arg(200)->Arg(500)->Arg(1024)
+
+static void Attach(pid_t pid) {
+ if (ptrace(PTRACE_ATTACH, pid, 0, 0) == -1) {
+ perror("Failed to attach");
+ abort();
+ }
+
+ siginfo_t si;
+ // Wait for up to 5 seconds.
+ for (size_t i = 0; i < 5000; i++) {
+ if (ptrace(PTRACE_GETSIGINFO, pid, 0, &si) == 0) {
+ return;
+ }
+ usleep(1000);
+ }
+ printf("Remote process failed to stop in five seconds.\n");
+ abort();
+}
+
+class ScopedPidReaper {
+ public:
+ ScopedPidReaper(pid_t pid) : pid_(pid) {}
+ ~ScopedPidReaper() {
+ kill(pid_, SIGKILL);
+ waitpid(pid_, nullptr, 0);
+ }
+
+ private:
+ pid_t pid_;
+};
+
+static size_t ProcessVmRead(pid_t pid, uint64_t remote_src, void* dst, size_t len) {
+ struct iovec dst_iov = {
+ .iov_base = dst, .iov_len = len,
+ };
+
+ struct iovec src_iov = {
+ .iov_base = reinterpret_cast<void*>(remote_src), .iov_len = len,
+ };
+
+ ssize_t rc = process_vm_readv(pid, &dst_iov, 1, &src_iov, 1, 0);
+ return rc == -1 ? 0 : rc;
+}
+
+static bool PtraceReadLong(pid_t pid, uint64_t addr, long* value) {
+ // ptrace() returns -1 and sets errno when the operation fails.
+ // To disambiguate -1 from a valid result, we clear errno beforehand.
+ errno = 0;
+ *value = ptrace(PTRACE_PEEKTEXT, pid, reinterpret_cast<void*>(addr), nullptr);
+ if (*value == -1 && errno) {
+ return false;
+ }
+ return true;
+}
+
+static size_t PtraceRead(pid_t pid, uint64_t addr, void* dst, size_t bytes) {
+ size_t bytes_read = 0;
+ long data;
+ for (size_t i = 0; i < bytes / sizeof(long); i++) {
+ if (!PtraceReadLong(pid, addr, &data)) {
+ return bytes_read;
+ }
+ memcpy(dst, &data, sizeof(long));
+ dst = reinterpret_cast<void*>(reinterpret_cast<uintptr_t>(dst) + sizeof(long));
+ addr += sizeof(long);
+ bytes_read += sizeof(long);
+ }
+
+ size_t left_over = bytes & (sizeof(long) - 1);
+ if (left_over) {
+ if (!PtraceReadLong(pid, addr, &data)) {
+ return bytes_read;
+ }
+ memcpy(dst, &data, left_over);
+ bytes_read += left_over;
+ }
+ return bytes_read;
+}
+
+static void CreateRemoteProcess(size_t size, void** map, pid_t* pid) {
+ *map = mmap(nullptr, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+ if (*map == MAP_FAILED) {
+ perror("Can't allocate memory");
+ abort();
+ }
+ memset(*map, 0xaa, size);
+
+ if ((*pid = fork()) == 0) {
+ for (volatile int i = 0;; i++)
+ ;
+ exit(1);
+ }
+ if (*pid < 0) {
+ perror("Failed to fork");
+ abort();
+ }
+ Attach(*pid);
+ // Don't need this map in the current process any more.
+ munmap(*map, size);
+}
+
+static void BM_read_with_ptrace(benchmark::State& state) {
+ void* map;
+ pid_t pid;
+ CreateRemoteProcess(state.range(0), &map, &pid);
+ ScopedPidReaper reap(pid);
+
+ std::vector<uint8_t> read_buffer(state.range(0));
+ uint64_t addr = reinterpret_cast<uint64_t>(map);
+ while (state.KeepRunning()) {
+ if (PtraceRead(pid, addr, read_buffer.data(), read_buffer.size()) != read_buffer.size()) {
+ printf("Unexpected bad read.\n");
+ abort();
+ }
+ }
+ ptrace(PTRACE_DETACH, pid, 0, 0);
+}
+BENCHMARK(BM_read_with_ptrace)->AT_COMMON_SIZES;
+
+static void BM_read_with_process_vm_read(benchmark::State& state) {
+ void* map;
+ pid_t pid;
+ CreateRemoteProcess(state.range(0), &map, &pid);
+ ScopedPidReaper reap(pid);
+
+ std::vector<uint8_t> read_buffer(state.range(0));
+ uint64_t addr = reinterpret_cast<uint64_t>(map);
+ while (state.KeepRunning()) {
+ if (ProcessVmRead(pid, addr, read_buffer.data(), read_buffer.size()) != read_buffer.size()) {
+ printf("Unexpected bad read.\n");
+ abort();
+ }
+ }
+ ptrace(PTRACE_DETACH, pid, 0, 0);
+}
+BENCHMARK(BM_read_with_process_vm_read)->AT_COMMON_SIZES;
+
+static void BM_read_with_backtrace_object(benchmark::State& state) {
+ void* map;
+ pid_t pid;
+ CreateRemoteProcess(state.range(0), &map, &pid);
+ ScopedPidReaper reap(pid);
+
+ std::unique_ptr<Backtrace> backtrace(Backtrace::Create(pid, BACKTRACE_CURRENT_THREAD));
+ if (backtrace.get() == nullptr) {
+ printf("Failed to create backtrace.\n");
+ abort();
+ }
+
+ uint64_t addr = reinterpret_cast<uint64_t>(map);
+ std::vector<uint8_t> read_buffer(state.range(0));
+ while (state.KeepRunning()) {
+ if (backtrace->Read(addr, read_buffer.data(), read_buffer.size()) != read_buffer.size()) {
+ printf("Unexpected bad read.\n");
+ abort();
+ }
+ }
+ ptrace(PTRACE_DETACH, pid, 0, 0);
+}
+BENCHMARK(BM_read_with_backtrace_object)->AT_COMMON_SIZES;