/*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * 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 <folly/experimental/symbolizer/Symbolizer.h>

#include <link.h>
#include <ucontext.h>

#include <climits>
#include <cstdio>
#include <cstdlib>
#include <iostream>

#ifdef __GLIBCXX__
#include <ext/stdio_filebuf.h>
#include <ext/stdio_sync_filebuf.h>
#endif

#include <folly/Conv.h>
#include <folly/FileUtil.h>
#include <folly/Memory.h>
#include <folly/ScopeGuard.h>
#include <folly/String.h>

#include <folly/experimental/symbolizer/Dwarf.h>
#include <folly/experimental/symbolizer/Elf.h>
#include <folly/experimental/symbolizer/LineReader.h>
#include <folly/portability/SysMman.h>
#include <folly/portability/Unistd.h>

/*
 * This is declared in `link.h' on Linux platforms, but apparently not on the
 * Mac version of the file.  It's harmless to declare again, in any case.
 *
 * Note that declaring it with `extern "C"` results in linkage conflicts.
 */
extern struct r_debug _r_debug;

namespace folly {
namespace symbolizer {

namespace {

ElfCache* defaultElfCache() {
  static constexpr size_t defaultCapacity = 500;
  static auto cache = new ElfCache(defaultCapacity);
  return cache;
}

void setSymbolizedFrame(
    SymbolizedFrame& frame,
    const std::shared_ptr<ElfFile>& file,
    uintptr_t address,
    LocationInfoMode mode,
    folly::Range<SymbolizedFrame*> extraInlineFrames = {}) {
  frame.clear();
  frame.found = true;

  auto sym = file->getDefinitionByAddress(address);
  if (!sym.first) {
    return;
  }

  frame.addr = address;
  frame.file = file;
  frame.name = file->getSymbolName(sym);

  Dwarf(file.get())
      .findAddress(address, mode, frame.location, extraInlineFrames);
}

} // namespace

Symbolizer::Symbolizer(
    ElfCacheBase* cache,
    LocationInfoMode mode,
    size_t symbolCacheSize)
    : cache_(cache ? cache : defaultElfCache()), mode_(mode) {
  if (symbolCacheSize > 0) {
    symbolCache_.emplace(folly::in_place, symbolCacheSize);
  }
}

void Symbolizer::symbolize(
    folly::Range<const uintptr_t*> addrs,
    folly::Range<SymbolizedFrame*> frames) {
  size_t addrCount = addrs.size();
  size_t frameCount = frames.size();
  size_t remaining = 0;
  for (size_t i = 0; i < addrCount; ++i) {
    auto& frame = frames[i];
    if (!frame.found) {
      ++remaining;
      frame.clear();
    }
  }

  if (remaining == 0) { // we're done
    return;
  }

  if (_r_debug.r_version != 1) {
    return;
  }

  char selfPath[PATH_MAX + 8];
  ssize_t selfSize;
  if ((selfSize = readlink("/proc/self/exe", selfPath, PATH_MAX + 1)) == -1) {
    // Something has gone terribly wrong.
    return;
  }
  selfPath[selfSize] = '\0';

  for (size_t i = 0; i < addrCount; i++) {
    frames[i].addr = addrs[i];
  }

  // Find out how many frames were filled in.
  auto countFrames = [](folly::Range<SymbolizedFrame*> framesRange) {
    return std::distance(
        framesRange.begin(),
        std::find_if(framesRange.begin(), framesRange.end(), [&](auto frame) {
          return !frame.found;
        }));
  };

  for (auto lmap = _r_debug.r_map; lmap != nullptr && remaining != 0;
       lmap = lmap->l_next) {
    // The empty string is used in place of the filename for the link_map
    // corresponding to the running executable.  Additionally, the `l_addr' is
    // 0 and the link_map appears to be first in the list---but none of this
    // behavior appears to be documented, so checking for the empty string is
    // as good as anything.
    auto const objPath = lmap->l_name[0] != '\0' ? lmap->l_name : selfPath;

    auto const elfFile = cache_->getFile(objPath);
    if (!elfFile) {
      continue;
    }

    for (size_t i = 0; i < addrCount && remaining != 0; ++i) {
      auto& frame = frames[i];
      if (frame.found) {
        continue;
      }

      auto const addr = frame.addr;
      if (symbolCache_) {
        // Need a write lock, because EvictingCacheMap brings found item to
        // front of eviction list.
        auto lockedSymbolCache = symbolCache_->wlock();

        auto const iter = lockedSymbolCache->find(addr);
        if (iter != lockedSymbolCache->end()) {
          size_t numCachedFrames = countFrames(folly::range(iter->second));
          // 1 entry in cache is the non-inlined function call and that one
          // already has space reserved at `frames[i]`
          auto numInlineFrames = numCachedFrames - 1;
          if (numInlineFrames <= frameCount - addrCount) {
            // Move the rest of the frames to make space for inlined frames.
            std::move_backward(
                frames.begin() + i + 1,
                frames.begin() + addrCount,
                frames.begin() + addrCount + numInlineFrames);
            // Overwrite frames[i] too (the non-inlined function call entry).
            std::copy(
                iter->second.begin(),
                iter->second.begin() + numInlineFrames + 1,
                frames.begin() + i);
            i += numInlineFrames;
            addrCount += numInlineFrames;
          }
          continue;
        }
      }

      // Get the unrelocated, ELF-relative address by normalizing via the
      // address at which the object is loaded.
      auto const adjusted = addr - reinterpret_cast<uintptr_t>(lmap->l_addr);
      size_t numInlined = 0;
      if (elfFile->getSectionContainingAddress(adjusted)) {
        if (mode_ == LocationInfoMode::FULL_WITH_INLINE &&
            frameCount > addrCount) {
          size_t maxInline = std::min<size_t>(
              Dwarf::kMaxInlineLocationInfoPerFrame, frameCount - addrCount);
          // First use the trailing empty frames (index starting from addrCount)
          // to get the inline call stack, then rotate these inline functions
          // before the caller at `frame[i]`.
          folly::Range<SymbolizedFrame*> inlineFrameRange(
              frames.begin() + addrCount,
              frames.begin() + addrCount + maxInline);
          setSymbolizedFrame(frame, elfFile, adjusted, mode_, inlineFrameRange);

          numInlined = countFrames(inlineFrameRange);
          // Rotate inline frames right before its caller frame.
          std::rotate(
              frames.begin() + i,
              frames.begin() + addrCount,
              frames.begin() + addrCount + numInlined);
          addrCount += numInlined;
        } else {
          setSymbolizedFrame(frame, elfFile, adjusted, mode_);
        }
        --remaining;
        if (symbolCache_) {
          // frame may already have been set here.  That's ok, we'll just
          // overwrite, which doesn't cause a correctness problem.
          CachedSymbolizedFrames cacheFrames;
          std::copy(
              frames.begin() + i,
              frames.begin() + i + std::min(numInlined + 1, cacheFrames.size()),
              cacheFrames.begin());
          symbolCache_->wlock()->set(addr, cacheFrames);
        }
        // Skip over the newly added inlined items.
        i += numInlined;
      }
    }
  }
}

namespace {
constexpr char kHexChars[] = "0123456789abcdef";
constexpr auto kAddressColor = SymbolizePrinter::Color::BLUE;
constexpr auto kFunctionColor = SymbolizePrinter::Color::PURPLE;
constexpr auto kFileColor = SymbolizePrinter::Color::DEFAULT;
} // namespace

constexpr char AddressFormatter::bufTemplate[];
constexpr std::array<const char*, SymbolizePrinter::Color::NUM>
    SymbolizePrinter::kColorMap;

AddressFormatter::AddressFormatter() {
  memcpy(buf_, bufTemplate, sizeof(buf_));
}

folly::StringPiece AddressFormatter::format(uintptr_t address) {
  // Can't use sprintf, not async-signal-safe
  static_assert(sizeof(uintptr_t) <= 8, "huge uintptr_t?");
  char* end = buf_ + sizeof(buf_) - 1 - (16 - 2 * sizeof(uintptr_t));
  char* p = end;
  *p-- = '\0';
  while (address != 0) {
    *p-- = kHexChars[address & 0xf];
    address >>= 4;
  }

  return folly::StringPiece(buf_, end);
}

void SymbolizePrinter::print(const SymbolizedFrame& frame) {
  if (options_ & TERSE) {
    printTerse(frame);
    return;
  }

  SCOPE_EXIT {
    color(Color::DEFAULT);
  };

  if (!(options_ & NO_FRAME_ADDRESS)) {
    color(kAddressColor);

    AddressFormatter formatter;
    doPrint(formatter.format(frame.addr));
  }

  const char padBuf[] = "                       ";
  folly::StringPiece pad(
      padBuf, sizeof(padBuf) - 1 - (16 - 2 * sizeof(uintptr_t)));

  color(kFunctionColor);
  if (!frame.found) {
    doPrint(" (not found)");
    return;
  }

  if (!frame.name || frame.name[0] == '\0') {
    doPrint(" (unknown)");
  } else {
    char demangledBuf[2048];
    demangle(frame.name, demangledBuf, sizeof(demangledBuf));
    doPrint(" ");
    doPrint(demangledBuf[0] == '\0' ? frame.name : demangledBuf);
  }

  if (!(options_ & NO_FILE_AND_LINE)) {
    color(kFileColor);
    char fileBuf[PATH_MAX];
    fileBuf[0] = '\0';
    if (frame.location.hasFileAndLine) {
      frame.location.file.toBuffer(fileBuf, sizeof(fileBuf));
      doPrint("\n");
      doPrint(pad);
      doPrint(fileBuf);

      char buf[22];
      uint32_t n = uint64ToBufferUnsafe(frame.location.line, buf);
      doPrint(":");
      doPrint(StringPiece(buf, n));
    }

    if (frame.location.hasMainFile) {
      char mainFileBuf[PATH_MAX];
      mainFileBuf[0] = '\0';
      frame.location.mainFile.toBuffer(mainFileBuf, sizeof(mainFileBuf));
      if (!frame.location.hasFileAndLine || strcmp(fileBuf, mainFileBuf)) {
        doPrint("\n");
        doPrint(pad);
        doPrint("-> ");
        doPrint(mainFileBuf);
      }
    }
  }
}

void SymbolizePrinter::color(SymbolizePrinter::Color color) {
  if ((options_ & COLOR) == 0 && ((options_ & COLOR_IF_TTY) == 0 || !isTty_)) {
    return;
  }
  if (static_cast<size_t>(color) >= kColorMap.size()) { // catches underflow too
    return;
  }
  doPrint(kColorMap[color]);
}

void SymbolizePrinter::println(const SymbolizedFrame& frame) {
  print(frame);
  doPrint("\n");
}

void SymbolizePrinter::printTerse(const SymbolizedFrame& frame) {
  if (frame.found && frame.name && frame.name[0] != '\0') {
    char demangledBuf[2048] = {0};
    demangle(frame.name, demangledBuf, sizeof(demangledBuf));
    doPrint(demangledBuf[0] == '\0' ? frame.name : demangledBuf);
  } else {
    // Can't use sprintf, not async-signal-safe
    static_assert(sizeof(uintptr_t) <= 8, "huge uintptr_t?");
    char buf[] = "0x0000000000000000";
    char* end = buf + sizeof(buf) - 1 - (16 - 2 * sizeof(uintptr_t));
    char* p = end;
    *p-- = '\0';
    auto address = frame.addr;
    while (address != 0) {
      *p-- = kHexChars[address & 0xf];
      address >>= 4;
    }
    doPrint(StringPiece(buf, end));
  }
}

void SymbolizePrinter::println(
    const SymbolizedFrame* frames,
    size_t frameCount) {
  for (size_t i = 0; i < frameCount; ++i) {
    println(frames[i]);
  }
}

namespace {

int getFD(const std::ios& stream) {
#if FOLLY_USE_LIBSTDCPP && FOLLY_HAS_RTTI
  std::streambuf* buf = stream.rdbuf();
  using namespace __gnu_cxx;

  {
    auto sbuf = dynamic_cast<stdio_sync_filebuf<char>*>(buf);
    if (sbuf) {
      return fileno(sbuf->file());
    }
  }
  {
    auto sbuf = dynamic_cast<stdio_filebuf<char>*>(buf);
    if (sbuf) {
      return sbuf->fd();
    }
  }
#else
  (void)stream;
#endif // __GNUC__
  return -1;
}

bool isColorfulTty(int options, int fd) {
  if ((options & SymbolizePrinter::TERSE) != 0 ||
      (options & SymbolizePrinter::COLOR_IF_TTY) == 0 || fd < 0 ||
      !::isatty(fd)) {
    return false;
  }
  auto term = ::getenv("TERM");
  return !(term == nullptr || term[0] == '\0' || strcmp(term, "dumb") == 0);
}

} // namespace

OStreamSymbolizePrinter::OStreamSymbolizePrinter(std::ostream& out, int options)
    : SymbolizePrinter(options, isColorfulTty(options, getFD(out))),
      out_(out) {}

void OStreamSymbolizePrinter::doPrint(StringPiece sp) {
  out_ << sp;
}

FDSymbolizePrinter::FDSymbolizePrinter(int fd, int options, size_t bufferSize)
    : SymbolizePrinter(options, isColorfulTty(options, fd)),
      fd_(fd),
      buffer_(bufferSize ? IOBuf::create(bufferSize) : nullptr) {}

FDSymbolizePrinter::~FDSymbolizePrinter() {
  flush();
}

void FDSymbolizePrinter::doPrint(StringPiece sp) {
  if (buffer_) {
    if (sp.size() > buffer_->tailroom()) {
      flush();
      writeFull(fd_, sp.data(), sp.size());
    } else {
      memcpy(buffer_->writableTail(), sp.data(), sp.size());
      buffer_->append(sp.size());
    }
  } else {
    writeFull(fd_, sp.data(), sp.size());
  }
}

void FDSymbolizePrinter::flush() {
  if (buffer_ && !buffer_->empty()) {
    writeFull(fd_, buffer_->data(), buffer_->length());
    buffer_->clear();
  }
}

FILESymbolizePrinter::FILESymbolizePrinter(FILE* file, int options)
    : SymbolizePrinter(options, isColorfulTty(options, fileno(file))),
      file_(file) {}

void FILESymbolizePrinter::doPrint(StringPiece sp) {
  fwrite(sp.data(), 1, sp.size(), file_);
}

void StringSymbolizePrinter::doPrint(StringPiece sp) {
  buf_.append(sp.data(), sp.size());
}

SafeStackTracePrinter::SafeStackTracePrinter(int fd)
    : fd_(fd),
      printer_(
          fd,
          SymbolizePrinter::COLOR_IF_TTY,
          size_t(64) << 10), // 64KiB
      addresses_(std::make_unique<FrameArray<kMaxStackTraceDepth>>()) {}

void SafeStackTracePrinter::flush() {
  printer_.flush();
  fsyncNoInt(fd_);
}

void SafeStackTracePrinter::printSymbolizedStackTrace() {
  // This function might run on an alternative stack allocated by
  // UnsafeSelfAllocateStackTracePrinter. Capturing a stack from
  // here is probably wrong.

  // Do our best to populate location info, process is going to terminate,
  // so performance isn't critical.
  SignalSafeElfCache elfCache_;
  Symbolizer symbolizer(&elfCache_, LocationInfoMode::FULL);
  symbolizer.symbolize(*addresses_);

  // Skip the top 2 frames captured by printStackTrace:
  // getStackTraceSafe
  // SafeStackTracePrinter::printStackTrace (captured stack)
  //
  // Leaving signalHandler on the stack for clarity, I think.
  printer_.println(*addresses_, 2);
}

void SafeStackTracePrinter::printStackTrace(bool symbolize) {
  SCOPE_EXIT {
    flush();
  };

  // Skip the getStackTrace frame
  if (!getStackTraceSafe(*addresses_)) {
    print("(error retrieving stack trace)\n");
  } else if (symbolize) {
    printSymbolizedStackTrace();
  } else {
    print("(safe mode, symbolizer not available)\n");
    AddressFormatter formatter;
    for (size_t i = 0; i < addresses_->frameCount; ++i) {
      print(formatter.format(addresses_->addresses[i]));
      print("\n");
    }
  }
}

FastStackTracePrinter::FastStackTracePrinter(
    std::unique_ptr<SymbolizePrinter> printer,
    size_t elfCacheSize,
    size_t symbolCacheSize)
    : elfCache_(
          elfCacheSize == 0
              ? nullptr
              : new ElfCache{std::max(countLoadedElfFiles(), elfCacheSize)}),
      printer_(std::move(printer)),
      symbolizer_(
          elfCache_ ? elfCache_.get() : defaultElfCache(),
          LocationInfoMode::FULL,
          symbolCacheSize) {}

FastStackTracePrinter::~FastStackTracePrinter() = default;

void FastStackTracePrinter::printStackTrace(bool symbolize) {
  SCOPE_EXIT {
    printer_->flush();
  };

  FrameArray<kMaxStackTraceDepth> addresses;

  if (!getStackTraceSafe(addresses)) {
    printer_->print("(error retrieving stack trace)\n");
  } else if (symbolize) {
    symbolizer_.symbolize(addresses);

    // Skip the top 2 frames:
    // getStackTraceSafe
    // FastStackTracePrinter::printStackTrace (here)
    printer_->println(addresses, 2);
  } else {
    printer_->print("(safe mode, symbolizer not available)\n");
    AddressFormatter formatter;
    for (size_t i = 0; i < addresses.frameCount; ++i) {
      printer_->print(formatter.format(addresses.addresses[i]));
      printer_->print("\n");
    }
  }
}

void FastStackTracePrinter::flush() {
  printer_->flush();
}

// Stack utilities used by UnsafeSelfAllocateStackTracePrinter
namespace {
// Size of mmap-allocated stack. Not to confuse with sigaltstack.
const size_t kMmapStackSize = 1 * 1024 * 1024;

using MmapPtr = std::unique_ptr<char, void (*)(char*)>;

MmapPtr getNull() {
  return MmapPtr(nullptr, [](char*) {});
}

// Assign a mmap-allocated stack to oucp.
// Return a non-empty smart pointer on success.
MmapPtr allocateStack(ucontext_t* oucp, size_t pageSize) {
  MmapPtr p(
      (char*)mmap(
          nullptr,
          kMmapStackSize,
          PROT_WRITE | PROT_READ,
          MAP_ANONYMOUS | MAP_PRIVATE,
          /* fd */ -1,
          /* offset */ 0),
      [](char* addr) {
        // Usually runs inside a fatal signal handler.
        // Error handling is skipped.
        munmap(addr, kMmapStackSize);
      });

  if (!p) {
    return getNull();
  }

  // Prepare read-only guard pages on both ends
  if (pageSize * 2 >= kMmapStackSize) {
    return getNull();
  }
  size_t upperBound = ((kMmapStackSize - 1) / pageSize) * pageSize;
  if (mprotect(p.get(), pageSize, PROT_NONE) != 0) {
    return getNull();
  }
  if (mprotect(p.get() + upperBound, kMmapStackSize - upperBound, PROT_NONE) !=
      0) {
    return getNull();
  }

  oucp->uc_stack.ss_sp = p.get() + pageSize;
  oucp->uc_stack.ss_size = upperBound - pageSize;
  oucp->uc_stack.ss_flags = 0;

  return p;
}

} // namespace

void UnsafeSelfAllocateStackTracePrinter::printSymbolizedStackTrace() {
  if (pageSizeUnchecked_ <= 0) {
    return;
  }

  ucontext_t cur;
  memset(&cur, 0, sizeof(cur));
  ucontext_t alt;
  memset(&alt, 0, sizeof(alt));

  if (getcontext(&alt) != 0) {
    return;
  }
  alt.uc_link = &cur;

  MmapPtr p = allocateStack(&alt, (size_t)pageSizeUnchecked_);
  if (!p) {
    return;
  }

  auto contextStart = [](UnsafeSelfAllocateStackTracePrinter* that) {
    that->SafeStackTracePrinter::printSymbolizedStackTrace();
  };

  makecontext(
      &alt,
      (void (*)())(void (*)(UnsafeSelfAllocateStackTracePrinter*))(
          contextStart),
      /* argc */ 1,
      /* arg */ this);
  // NOTE: swapcontext is not async-signal-safe
  if (swapcontext(&cur, &alt) != 0) {
    return;
  }
}

} // namespace symbolizer
} // namespace folly
