// Copyright 2021 The Abseil Authors
//
// 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
//
//     https://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 ABSL_DEBUGGING_INTERNAL_STACKTRACE_RISCV_INL_H_
#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_RISCV_INL_H_

// Generate stack trace for riscv

#include <sys/ucontext.h>

#include "absl/base/config.h"
#if defined(__linux__)
#include <sys/mman.h>
#include <ucontext.h>
#include <unistd.h>
#endif

#include <atomic>
#include <cassert>
#include <cstdint>
#include <iostream>

#include "absl/base/attributes.h"
#include "absl/debugging/internal/address_is_readable.h"
#include "absl/debugging/internal/vdso_support.h"
#include "absl/debugging/stacktrace.h"

static const uintptr_t kUnknownFrameSize = 0;

#if defined(__linux__)
// Returns the address of the VDSO __kernel_rt_sigreturn function, if present.
static const unsigned char *GetKernelRtSigreturnAddress() {
  constexpr uintptr_t kImpossibleAddress = 0;
  ABSL_CONST_INIT static std::atomic<uintptr_t> memoized(kImpossibleAddress);
  uintptr_t address = memoized.load(std::memory_order_relaxed);
  if (address != kImpossibleAddress) {
    return reinterpret_cast<const unsigned char *>(address);
  }

  address = reinterpret_cast<uintptr_t>(nullptr);

#if ABSL_HAVE_VDSO_SUPPORT
  absl::debugging_internal::VDSOSupport vdso;
  if (vdso.IsPresent()) {
    absl::debugging_internal::VDSOSupport::SymbolInfo symbol_info;
    // Symbol versioning pulled from arch/riscv/kernel/vdso/vdso.lds at v5.10.
    auto lookup = [&](int type) {
      return vdso.LookupSymbol("__kernel_rt_sigreturn", "LINUX_4.15", type,
                               &symbol_info);
    };
    if ((!lookup(STT_FUNC) && !lookup(STT_NOTYPE)) ||
        symbol_info.address == nullptr) {
      // Unexpected: VDSO is present, yet the expected symbol is missing or
      // null.
      assert(false && "VDSO is present, but doesn't have expected symbol");
    } else {
      if (reinterpret_cast<uintptr_t>(symbol_info.address) !=
          kImpossibleAddress) {
        address = reinterpret_cast<uintptr_t>(symbol_info.address);
      } else {
        assert(false && "VDSO returned invalid address");
      }
    }
  }
#endif

  memoized.store(address, std::memory_order_relaxed);
  return reinterpret_cast<const unsigned char *>(address);
}
#endif  // __linux__

// Compute the size of a stack frame in [low..high).  We assume that low < high.
// Return size of kUnknownFrameSize.
template <typename T>
static inline uintptr_t ComputeStackFrameSize(const T *low, const T *high) {
  const char *low_char_ptr = reinterpret_cast<const char *>(low);
  const char *high_char_ptr = reinterpret_cast<const char *>(high);
  return low < high ? high_char_ptr - low_char_ptr : kUnknownFrameSize;
}

// Given a pointer to a stack frame, locate and return the calling stackframe,
// or return null if no stackframe can be found. Perform sanity checks (the
// strictness of which is controlled by the boolean parameter
// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
template <bool STRICT_UNWINDING, bool WITH_CONTEXT>
ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS  // May read random elements from stack.
ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY   // May read random elements from stack.
static void ** NextStackFrame(void **old_frame_pointer, const void *uc) {
  //               .
  //               .
  //               .
  //   +-> +----------------+
  //   |   | return address |
  //   |   |   previous fp  |
  //   |   |      ...       |
  //   |   +----------------+ <-+
  //   |   | return address |   |
  //   +---|-  previous fp  |   |
  //       |      ...       |   |
  // $fp ->|----------------+   |
  //       | return address |   |
  //       |   previous fp -|---+
  // $sp ->|      ...       |
  //       +----------------+
  void **new_frame_pointer = reinterpret_cast<void **>(old_frame_pointer[-2]);
  bool check_frame_size = true;

#if defined(__linux__)
  if (WITH_CONTEXT && uc != nullptr) {
    // Check to see if next frame's return address is __kernel_rt_sigreturn.
    if (old_frame_pointer[-1] == GetKernelRtSigreturnAddress()) {
      const ucontext_t *ucv = static_cast<const ucontext_t *>(uc);
      // old_frame_pointer is not suitable for unwinding, look at ucontext to
      // discover frame pointer before signal.
      //
      // RISCV ELF psABI has the frame pointer at x8/fp/s0.
      // -- RISCV psABI Table 18.2
      void **const pre_signal_frame_pointer =
          reinterpret_cast<void **>(ucv->uc_mcontext.__gregs[8]);

      // Check the alleged frame pointer is actually readable. This is to
      // prevent "double fault" in case we hit the first fault due to stack
      // corruption.
      if (!absl::debugging_internal::AddressIsReadable(
              pre_signal_frame_pointer))
        return nullptr;

      // Alleged frame pointer is readable, use it for further unwinding.
      new_frame_pointer = pre_signal_frame_pointer;

      // Skip frame size check if we return from a signal.  We may be using an
      // alterate stack for signals.
      check_frame_size = false;
    }
  }
#endif

  // The RISCV ELF psABI mandates that the stack pointer is always 16-byte
  // aligned.
  // FIXME(abdulras) this doesn't hold for ILP32E which only mandates a 4-byte
  // alignment.
  if ((reinterpret_cast<uintptr_t>(new_frame_pointer) & 15) != 0)
    return nullptr;

  // Check frame size.  In strict mode, we assume frames to be under 100,000
  // bytes.  In non-strict mode, we relax the limit to 1MB.
  if (check_frame_size) {
    const uintptr_t max_size = STRICT_UNWINDING ? 100000 : 1000000;
    const uintptr_t frame_size =
        ComputeStackFrameSize(old_frame_pointer, new_frame_pointer);
    if (frame_size == kUnknownFrameSize || frame_size > max_size)
      return nullptr;
  }

  return new_frame_pointer;
}

template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS  // May read random elements from stack.
ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY   // May read random elements from stack.
static int UnwindImpl(void **result, int *sizes, int max_depth, int skip_count,
                      const void *ucp, int *min_dropped_frames) {
#if defined(__GNUC__)
  void **frame_pointer = reinterpret_cast<void **>(__builtin_frame_address(0));
#else
#error reading stack pointer not yet supported on this platform
#endif

  skip_count++;  // Skip the frame for this function.
  int n = 0;

  // The `frame_pointer` that is computed here points to the top of the frame.
  // The two words preceding the address are the return address and the previous
  // frame pointer.  To find a PC value associated with the current frame, we
  // need to go down a level in the call chain.  So we remember the return
  // address of the last frame seen.  This does not work for the first stack
  // frame, which belongs to `UnwindImp()` but we skip the frame for
  // `UnwindImp()` anyway.
  void *prev_return_address = nullptr;

  while (frame_pointer && n < max_depth) {
    // The absl::GetStackFrames routine si called when we are in some
    // informational context (the failure signal handler for example).  Use the
    // non-strict unwinding rules to produce a stack trace that is as complete
    // as possible (even if it contains a few bogus entries in some rare cases).
    void **next_frame_pointer =
        NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(frame_pointer, ucp);

    if (skip_count > 0) {
      skip_count--;
    } else {
      result[n] = prev_return_address;
      if (IS_STACK_FRAMES) {
        sizes[n] = ComputeStackFrameSize(frame_pointer, next_frame_pointer);
      }
      n++;
    }
    prev_return_address = frame_pointer[-1];
    frame_pointer = next_frame_pointer;
  }
  if (min_dropped_frames != nullptr) {
    // Implementation detail: we clamp the max of frames we are willing to
    // count, so as not to spend too much time in the loop below.
    const int kMaxUnwind = 200;
    int j = 0;
    for (; frame_pointer != nullptr && j < kMaxUnwind; j++) {
      frame_pointer =
          NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(frame_pointer, ucp);
    }
    *min_dropped_frames = j;
  }
  return n;
}

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace debugging_internal {
bool StackTraceWorksForTest() { return true; }
}  // namespace debugging_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif