base/profiler/frame_pointer_unwinder.cc

// Copyright 2021 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/profiler/frame_pointer_unwinder.h"

#include "base/check_op.h"
#include "base/notreached.h"
#include "base/numerics/clamped_math.h"
#include "base/profiler/module_cache.h"
#include "build/build_config.h"

#if BUILDFLAG(IS_APPLE)
#include <pthread/stack_np.h>
#endif

namespace {

// Given a frame pointer, returns the frame pointer of the calling stack
// frame and places the return address of the calling stack frame into
// `return_address`. Shim around `pthread_stack_frame_decode_np` where
// available since it handles pointer authentication on supported platforms.
// NB: The caller *must* ensure that there are 2+ uintptr_t's worth of memory at
// `frame_pointer`.
uintptr_t DecodeFrame(uintptr_t frame_pointer, uintptr_t* return_address) {
#if BUILDFLAG(IS_APPLE)
  if (__builtin_available(macOS 10.14, iOS 12, *))
    return pthread_stack_frame_decode_np(frame_pointer, return_address);
#endif
  const uintptr_t* fp = reinterpret_cast<uintptr_t*>(frame_pointer);
  uintptr_t next_frame = *fp;
  *return_address = *(fp + 1);
  return next_frame;
}

}  // namespace

namespace base {

FramePointerUnwinder::FramePointerUnwinder() = default;

bool FramePointerUnwinder::CanUnwindFrom(const Frame& current_frame) const {
  return current_frame.module && current_frame.module->IsNative();
}

UnwindResult FramePointerUnwinder::TryUnwind(RegisterContext* thread_context,
                                             uintptr_t stack_top,
                                             std::vector<Frame>* stack) {
  // We expect the frame corresponding to the |thread_context| register state to
  // exist within |stack|.
  DCHECK_GT(stack->size(), 0u);
#if defined(ARCH_CPU_ARM64)
  constexpr uintptr_t align_mask = 0x1;
#elif defined(ARCH_CPU_X86_64)
  constexpr uintptr_t align_mask = 0xf;
#endif

  uintptr_t next_frame = RegisterContextFramePointer(thread_context);
  uintptr_t frame_lower_bound = RegisterContextStackPointer(thread_context);
  const auto is_fp_valid = [&](uintptr_t fp) {
    // Ensure there's space on the stack to read two values: the caller's
    // frame pointer and the return address.
    return next_frame >= frame_lower_bound &&
           ClampAdd(next_frame, sizeof(uintptr_t) * 2) <= stack_top &&
           (next_frame & align_mask) == 0;
  };
  if (!is_fp_valid(next_frame))
    return UnwindResult::kAborted;

  for (;;) {
    if (!stack->back().module) {
      return UnwindResult::kAborted;
    }
    if (!stack->back().module->IsNative()) {
      // This is a non-native module associated with the auxiliary unwinder
      // (e.g. corresponding to a frame in V8 generated code). Report as
      // UNRECOGNIZED_FRAME to allow that unwinder to unwind the frame.
      return UnwindResult::kUnrecognizedFrame;
    }
    uintptr_t retaddr;
    uintptr_t frame = next_frame;
    next_frame = DecodeFrame(frame, &retaddr);
    frame_lower_bound = frame + 1;
    // If `next_frame` is 0, we've hit the root and `retaddr` isn't useful.
    // Bail without recording the frame.
    if (next_frame == 0)
      return UnwindResult::kCompleted;
    const ModuleCache::Module* module =
        module_cache()->GetModuleForAddress(retaddr);
    // V8 doesn't conform to the x86_64 ABI re: stack alignment. For V8 frames,
    // let the V8 unwinder determine whether the FP is valid or not.
    bool is_non_native_module = module && !module->IsNative();
    // If the FP doesn't look correct, don't record this frame.
    if (!is_non_native_module && !is_fp_valid(next_frame))
      return UnwindResult::kAborted;

    RegisterContextFramePointer(thread_context) = next_frame;
    RegisterContextInstructionPointer(thread_context) = retaddr;
    RegisterContextStackPointer(thread_context) = frame + sizeof(uintptr_t) * 2;
    stack->emplace_back(retaddr, module);
  }

  NOTREACHED();
  return UnwindResult::kCompleted;
}

}  // namespace base