NativeStackSampler implementation for Mac.

base/profiler/native_stack_sampler_mac.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <dlfcn.h>
+#include <mach/mach.h>
+#include <mach/thread_status.h>
+#include <mach-o/swap.h>
+#include <stdlib.h>
+
+#include <map>
+
+#include "base/logging.h"

[Mike Wittman, 2015/09/15 00:34:54]

unused?

[sydli, 2015/09/15 01:12:20]

Removed all of these.

+#include "base/md5.h"

[Mike Wittman, 2015/09/15 00:34:54]

unused?

+#include "base/profiler/native_stack_sampler.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/time/time.h"

[Mike Wittman, 2015/09/15 00:34:54]

unused?

+
+namespace base {
+
+namespace {
+
+// Copy of x86_64 thread context structure from x86_thread_state64_t type.
+// Copied struct since fields can have different names on different versions of
+// Darwin.
+struct ThreadContext {
+  uint64_t rax;
+  uint64_t rbx;
+  uint64_t rcx;
+  uint64_t rdx;
+  uint64_t rdi;
+  uint64_t rsi;
+  uint64_t rbp;
+  uint64_t rsp;
+  uint64_t r8;
+  uint64_t r9;
+  uint64_t r10;
+  uint64_t r11;
+  uint64_t r12;
+  uint64_t r13;
+  uint64_t r14;
+  uint64_t r15;
+  uint64_t rip;
+  uint64_t rflags;
+  uint64_t cs;
+  uint64_t fs;
+  uint64_t gs;
+};
+
+// Struct for stack walking (represents stack state on any function call that
+// pushes a frame pointer).
+struct StackFrame {
+  // Pointer to caller's frame (rbp).
+  uintptr_t prev;
+  // Address in caller for callee to return to.
+  uintptr_t return_addr;
+};
+
+// Overwrites |dst| with StackFrame referenced in |src|. Returns true if stack
+// jump was successful. Failure implies address in |src| is corrupt.
+bool SafeJump(uintptr_t src, StackFrame* dst) {
+  vm_size_t ignored_bytes_copied = 0;
+  return vm_read_overwrite(mach_task_self(), (vm_address_t)src,

[Mike Wittman, 2015/09/15 00:34:54]

use C++-style casts

[sydli, 2015/09/15 01:12:19]

Done.

+                           (vm_size_t)sizeof(StackFrame), (vm_address_t)dst,
+                           &ignored_bytes_copied) == KERN_SUCCESS;
+}
+
+// Functions related to retrieving Mach-O Identifer
+//
+// These functions were cannibalized from Mach-O Identifier procedures found in
+// breakpad/src/common/mac. Support for non-X86_64 architectures and MD5 IDs
+// were removed to simplify the code.
+
+// Returns offset in bytes where the x86_64 header is located in binary
+// loaded at |module_addr|. Returns 0 if |module_addr| is not a valid FAT
+// Mach-O binary or has not been built for x86_64.
+off_t GetMach64HeaderOffset(const void* module_addr) {
+  fat_header hdr;
+  memcpy(&hdr, module_addr, sizeof(hdr));
+  if (hdr.magic != FAT_MAGIC && hdr.magic != FAT_CIGAM)
+    return 0;
+
+  if (hdr.magic == FAT_CIGAM)
+    swap_fat_header(&hdr, NXHostByteOrder());
+
+  // Search all FAT architectures for x86_64.
+  off_t offset = sizeof(hdr);
+  fat_arch arch;
+  for (uint32_t i = 0; i < hdr.nfat_arch; ++i) {
+    memcpy(&arch, reinterpret_cast<const char*>(module_addr) + offset,
+           sizeof(arch));
+
+    if (NXHostByteOrder() != NX_BigEndian)
+      swap_fat_arch(&arch, 1, NXHostByteOrder());
+
+    if (arch.cputype == CPU_TYPE_X86_64)
+      return arch.offset;
+    offset += sizeof(arch);
+  }
+  return 0;
+}
+
+// Returns true if Mach-O binary at |module_addr| was built specifically for
+// x86_64 cpu architecture.
+bool IsX64Header(const void* module_addr) {
+  mach_header_64 hdr;
+  memcpy(&hdr, module_addr, sizeof(hdr));
+  if (hdr.magic != MH_MAGIC_64 && hdr.magic != MH_CIGAM_64)
+    return false;
+  if (hdr.magic == MH_CIGAM_64)
+    swap_mach_header_64(&hdr, NXHostByteOrder());
+
+  return (hdr.cputype == CPU_TYPE_X86_64);

[Mike Wittman, 2015/09/15 00:34:54]

nit: no parens

[sydli, 2015/09/15 01:12:19]

Done.

+}
+
+// Fills |id| with the UUID of the x86_64 Mach-O binary loaded at |module_addr|.
+// |offset| is the offset in bytes into |module_addr| where the x86_64 header
+// is located. |offset| is only relevant if binary is FAT and contains
+// multiple architecture headers. See spec here:
+// https://developer.apple.com/library/mac/documentation/DeveloperTools/Conceptual/MachORuntime/
+// Returns false if header is malformed or the
+// header does not specify the UUID load command.
+bool GetX64UUIDAt(const void* module_addr, unsigned char id[16], off_t offset) {
+  mach_header_64 hdr;
+  if (!memcpy(&hdr, reinterpret_cast<const char*>(module_addr) + offset,
+              sizeof(hdr)) ||
+      (hdr.magic != MH_MAGIC_64 && hdr.magic != MH_CIGAM_64)) {
+    return false;
+  }
+
+  bool swap = hdr.magic == MH_CIGAM_64;
+  if (swap)
+    swap_mach_header_64(&hdr, NXHostByteOrder());
+
+  // Search all load commands for UUID command.
+  offset += sizeof(hdr);
+  load_command cmd;
+  for (uint32_t i = 0; i < hdr.ncmds; ++i) {
+    const void* command_loc =
+        reinterpret_cast<const char*>(module_addr) + offset;
+    memcpy(&cmd, command_loc, sizeof(cmd));
+
+    if (swap)
+      swap_load_command(&cmd, NXHostByteOrder());
+    if (cmd.cmd == LC_UUID) {
+      uuid_command uuid_cmd;
+      memcpy(&uuid_cmd, command_loc, sizeof(uuid_cmd));
+      if (swap)
+        swap_uuid_command(&uuid_cmd, NXHostByteOrder());
+
+      static_assert(sizeof(uuid_cmd.uuid) == 16,
+                    "UUID field of UUID command should be 16 bytes.");
+      memcpy(id, &uuid_cmd.uuid, sizeof(uuid_cmd));
+      return true;
+    }
+    offset += cmd.cmdsize;
+  }
+  return false;
+}
+
+// Fills |id| with Mach-O UUID retrieved from Mach-O binary loaded at
+// |module_addr|. This function returns false if the binary was not built for
+// X86_64 or if UUID cannot be found.
+bool GetUUID(const void* module_addr, unsigned char id[16]) {
+  off_t offset = 0;
+  if (!IsX64Header(module_addr) &&

[Mike Wittman, 2015/09/15 00:34:54]

shouldn't this be || ?

[sydli, 2015/09/15 01:12:19]

No, if it's not an x86_64-exclusive module it could be a module that supports
multiple archs, so it searches for the appropriate offset into the module. If it
can't find the offset either, then returns false. Added comment to indicate
this.

+      !(offset = GetMach64HeaderOffset(module_addr)))
+    return false;
+  return GetX64UUIDAt(module_addr, id, offset);
+}
+
+// Returns hex encoding of a 16-byte ID for binary loaded at |module_addr|.
+// Returns empty string if UUID cannot be found at |module_addr|.
+std::string GetUniqueId(const void* module_addr) {
+  unsigned char id[16];
+  if (!GetUUID(module_addr, id))
+    return "";
+  return HexEncode(id, 16);
+}
+
+// Functions related to grabbing a stack trace --------------------------------
+
+// Fills |state| with |target_thread|'s context.
+bool GetThreadState(thread_act_t target_thread, ThreadContext* state) {

[Mike Wittman, 2015/09/15 00:34:54]

can we call this GetThreadContext?

[sydli, 2015/09/15 01:12:19]

Done.

+  mach_msg_type_number_t count =
+      static_cast<mach_msg_type_number_t>(MACHINE_THREAD_STATE_COUNT);
+  return thread_get_state(target_thread, x86_THREAD_STATE64,
+                          reinterpret_cast<thread_state_t>(state),
+                          &count) == KERN_SUCCESS;
+}
+
+// Walks |thread_handle|'s stack and fills |instruction_pointers|.
+// Returns number of frames in stack, unless there's a corrupt frame pointer
+// (likely if module compiled with -fno_omit_frame_pointer), in which this
+// function will return the number of frames up until the frame with a corrupt
+// frame pointer. This procedure occurs while thread is suspended, so it should
+// take as little time as possible.
+int RecordStack(mach_port_t thread_handle,
+                int instruction_pointers_size,

[Mike Wittman, 2015/09/15 00:34:54]

can we call this max_stack_size, as in the Windows code?

[sydli, 2015/09/15 01:12:19]

Changed back to max_stack_size for consistency with Windows profiler.

+                uintptr_t instruction_pointers[]) {
+  ThreadContext state;
+  if (!GetThreadState(thread_handle, &state))
+    return 0;
+
+  StackFrame frame;
+  frame.prev = state.rbp;
+  int i = 0;
+  for (; i < instruction_pointers_size; i++) {
+    // Three cases for end-of-stack condition:
+    //   1) We tried to jump off the stack.
+    //   2) We jumped to a lower address.
+    //   3) We reached a return (instruction) address of 0.
+    uintptr_t old_esp = frame.prev;
+    if (!SafeJump(frame.prev, &frame) || frame.prev < old_esp ||
+        !frame.return_addr) {
+      return i;
+    }
+    instruction_pointers[i] = frame.return_addr;
+  }
+  return i;
+}
+
+// Adds library referenced by |instruction_pointer| to |sample| and |modules|.
+// Records library's (1) filepath, (2) base address, and (3) unique ID.
+void AddModule(StackSamplingProfiler::Sample* sample,
+               std::vector<StackSamplingProfiler::Module>* modules,
+               std::map<void*, size_t>* module_to_index,
+               const uintptr_t instruction_pointer) {
+  char filepath[PATH_MAX + 1];
+  Dl_info inf;
+  dladdr(reinterpret_cast<const void*>(instruction_pointer), &inf);
+  auto module_index = module_to_index->find(inf.dli_fbase);
+  if (module_index == module_to_index->end()) {
+    realpath(inf.dli_fname, filepath);
+    StackSamplingProfiler::Module module(
+        inf.dli_fbase, GetUniqueId(inf.dli_fbase), base::FilePath(filepath));
+    modules->push_back(module);
+
+    module_index = module_to_index->
+        insert(std::make_pair(inf.dli_fbase, modules->size() - 1)).first;
+  }
+  sample->push_back(StackSamplingProfiler::Frame(
+      reinterpret_cast<const void*>(instruction_pointer),
+      module_index->second));
+}
+
+// Fills |sample| with Frames and Modules referenced by |instruction_pointers|.
+void FillSample(const uintptr_t instruction_pointers[],
+                std::vector<StackSamplingProfiler::Module>* modules,
+                int stack_depth,
+                StackSamplingProfiler::Sample* sample) {
+  std::map<void*, size_t> module_index;

[Mike Wittman, 2015/09/15 00:34:54]

This needs to be a member variable, as in the Windows code. Otherwise the same
module will be added to |modules| each time it appears in a sample.

Also, use const void* for the key to be consistent with the rest of the code
that deals with memory addresses.

In general, can you mimic the names and logic of corresponding functions in the
Windows code, where it makes sense to do so? Limiting variation to only where
necessary makes it easier to understand both pieces of code in conjunction.

[sydli, 2015/09/15 01:12:19]

Sure.

+  for (int i = 0; i < stack_depth; i++) {
+    AddModule(sample, modules, &module_index, instruction_pointers[i]);
+  }
+}
+
+// NativeStackSamplerMac ------------------------------------------------------
+
+class NativeStackSamplerMac : public NativeStackSampler {
+ public:
+  explicit NativeStackSamplerMac(pid_t thread_handle);
+  ~NativeStackSamplerMac() override;
+
+  // StackSamplingProfiler::NativeStackSampler:
+  void ProfileRecordingStarting(
+      std::vector<StackSamplingProfiler::Module>* modules) override;
+  void RecordStackSample(StackSamplingProfiler::Sample* sample) override;
+  void ProfileRecordingStopped() override;
+
+  static const int kMaxStackSize = 64;

[Mike Wittman, 2015/09/15 00:34:54]

this can be a local variable in RecordStackSample()

(constants should be declared as local as possible to the code that uses them)

[sydli, 2015/09/15 01:12:19]

Done.

+
+ private:
+  mach_port_t thread_handle_;
+
+  // Weak. Points to the modules associated with the profile being recorded
+  // between ProfileRecordingStarting() and ProfileRecordingStopped().
+  std::vector<StackSamplingProfiler::Module>* current_modules_;
+
+  DISALLOW_COPY_AND_ASSIGN(NativeStackSamplerMac);
+};
+
+// The PlatformThreadId of the given thread is actually a typedef of
+// mach_port_t.
+// (base/threading/platform_thread_posix.cc:128)
+NativeStackSamplerMac::NativeStackSamplerMac(pid_t thread_handle)
+    : thread_handle_(static_cast<mach_port_t>(thread_handle)) {}

[Mike Wittman, 2015/09/15 00:34:54]

current_modules_(nullptr)

[sydli, 2015/09/15 01:12:20]

Done.

+
+NativeStackSamplerMac::~NativeStackSamplerMac() {}
+
+void NativeStackSamplerMac::ProfileRecordingStarting(
+    std::vector<StackSamplingProfiler::Module>* modules) {
+  current_modules_ = modules;
+}
+
+void NativeStackSamplerMac::RecordStackSample(
+    StackSamplingProfiler::Sample* sample) {
+  DCHECK(current_modules_);
+  uintptr_t instruction_pointers[kMaxStackSize] = {0};
+
+  thread_suspend(thread_handle_);
+  int stack_depth =
+      RecordStack(thread_handle_, kMaxStackSize, instruction_pointers);
+  thread_resume(thread_handle_);
+  FillSample(instruction_pointers, current_modules_, stack_depth, sample);
+}
+
+void NativeStackSamplerMac::ProfileRecordingStopped() {
+  current_modules_ = nullptr;
+}
+
+}  // namespace
+
+scoped_ptr<NativeStackSampler> NativeStackSampler::Create(
+    PlatformThreadId thread_id) {
+#if defined(OS_MACOSX) && !defined(OS_NACL)

[Mike Wittman, 2015/09/15 00:34:54]

you can remove the "defined(OS_MACOSX)", and exclusion from the NACL compile is
better dealt with in the build files

[sydli, 2015/09/15 01:12:19]

Done.

+  return scoped_ptr<NativeStackSampler>(new NativeStackSamplerMac(thread_id));
+#endif
+  return scoped_ptr<NativeStackSampler>();
+}
+
+}  // namespace base