src/lib/zxdump/dump.cc

// Copyright 2022 The Fuchsia 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 "lib/zxdump/dump.h"

#include <lib/stdcompat/span.h>
#include <zircon/assert.h>
#include <zircon/syscalls/debug.h>
#include <zircon/syscalls/exception.h>

#include <array>
#include <cassert>
#include <cstdint>
#include <cstdlib>
#include <limits>
#include <map>
#include <optional>
#include <tuple>
#include <vector>

#include "core.h"

namespace zxdump {

namespace {

// This collects a bunch of note data, header and payload ByteView items.  The
// actual data the items point to is stored in Collector::notes_.
class NoteData {
 public:
  using Vector = std::vector<ByteView>;

  NoteData() = default;
  NoteData(NoteData&&) = default;
  NoteData& operator=(NoteData&&) = default;

  size_t size() const { return data_.size(); }

  size_t size_bytes() const { return size_bytes_; }

  void push_back(ByteView data) {
    ZX_DEBUG_ASSERT(data.size() % NoteAlign() == 0);
    if (!data.empty()) {
      data_.push_back(data);
      size_bytes_ += data.size();
    }
  }

  Vector take() && { return std::move(data_); }

 private:
  Vector data_;
  size_t size_bytes_ = 0;
};

// This represents one note header, with name and padding but no desc.
template <size_t NameSize>
class NoteHeader {
 public:
  NoteHeader() = delete;
  constexpr NoteHeader(const NoteHeader&) = default;
  constexpr NoteHeader& operator=(const NoteHeader&) = default;

  constexpr NoteHeader(std::string_view name, uint32_t descsz, uint32_t type)
      : nhdr_{.namesz = NameSize + 1, .descsz = descsz, .type = type} {
    assert(name.size() == NameSize);
    name.copy(name_, NameSize);
  }

  ByteView bytes() const {
    return {
        reinterpret_cast<const std::byte*>(this),
        sizeof(*this),
    };
  }

  constexpr void set_size(uint32_t descsz) { nhdr_.descsz = descsz; }

 private:
  static constexpr size_t kAlignedSize_ = NoteAlign(NameSize + 1);
  static_assert(kAlignedSize_ < std::numeric_limits<uint32_t>::max());

  Elf::Nhdr nhdr_;
  char name_[kAlignedSize_] = {};
};

// Each note format has an object in notes_ of a NoteBase type.
// The Type is the n_type field for the ELF note header.
// The Class represents a set of notes handled the same way.
// It provides the ELF note name, as well as other details used below.
template <typename Class, uint32_t Type>
class NoteBase {
 public:
  void AddToNoteData(NoteData& notes) const {
    if (!data_.empty()) {
      notes.push_back(header_.bytes());
      notes.push_back(data_);
    }
  }

  bool empty() const { return data_.empty(); }

  const auto& header() const { return header_; }
  auto& header() { return header_; }

  size_t size_bytes() const { return empty() ? 0 : header_.bytes().size() + data_.size(); }

  void clear() { data_ = {}; }

 protected:
  // The subclass Collect method calls this when it might have data.
  void Emplace(ByteView data) {
    if (!data.empty()) {
      ZX_ASSERT(data.size() <= std::numeric_limits<uint32_t>::max());
      header_.set_size(static_cast<uint32_t>(data.size()));
      data_ = data;
    }
  }

 private:
  // This holds the storage for the note header that NoteData points into.
  decltype(Class::MakeHeader(Type)) header_ = Class::MakeHeader(Type);

  // This points into the subclass storage for the note contents.
  // It's empty until the subclass calls Emplace.
  ByteView data_;
};

// Each class derived from NoteBase uses a core.h kFooNoteName constant in:
// ```
//   static constexpr auto MakeHeader = kMakeNote<kFooNoteName>;
// ```
template <const std::string_view& Name>
constexpr auto kMakeNote = [](uint32_t type) { return NoteHeader<Name.size()>(Name, 0, type); };

// This is called with each note (classes derived from NoteBase) when its
// information is required.  It can be called more than once, so it does
// nothing if it's already collected the data.  Each NoteBase subclass below
// has a Collect(const Handle&)->fitx::result<Error> method that should call
// NoteBase::Emplace when it has acquired data, and then won't be called again.
constexpr auto CollectNote = [](const auto& handle, auto& note) -> fitx::result<Error> {
  if (note.empty()) {
    return note.Collect(handle);
  }
  return fitx::ok();
};

// This doesn't need to be templated as specifically as InfoNote itself.  The
// GetInfo work is the same for all get_info topics whose data have the same
// size and alignment, so it's factored out that way here.

template <size_t Size, size_t Align>
using AlignedStorageVector = std::vector<std::aligned_storage_t<Size, Align>>;

template <typename T>
using InfoVector = AlignedStorageVector<sizeof(T), alignof(T)>;

template <size_t Align, size_t Size>
fitx::result<Error, AlignedStorageVector<Size, Align>> GetInfo(
    const zx::handle& task, zx_object_info_topic_t topic, AlignedStorageVector<Size, Align> data) {
  // Start with a buffer of at least one but reuse any larger old buffer.
  if (data.empty()) {
    data.resize(1);
  }
  while (true) {
    // Use as much space as is handy.
    data.resize(data.capacity());

    // See how much there is available and how much fits in the buffer.
    size_t actual, avail;
    zx_status_t status = task.get_info(topic, data.data(), data.size() * Size, &actual, &avail);
    if (status != ZX_OK) {
      return fitx::error(Error{"zx_object_get_info", status});
    }

    if (actual == avail) {
      // This is all the data.
      data.resize(avail);
      data.shrink_to_fit();
      return fitx::ok(std::move(data));
    }

    // There is more data.  Make the buffer at least as big as is needed.
    if (data.size() < avail) {
      data.resize(avail);
    }
  }
}

// Notes based on zx_object_get_info calls use this.
// For some types, the size is variable.
// We treat them all as variable.
template <typename Class, zx_object_info_topic_t Topic, typename T>
class InfoNote : public NoteBase<Class, Topic> {
 public:
  fitx::result<Error> Collect(const typename Class::Handle& task) {
    auto result =
        GetInfo<alignof(T), sizeof(T)>(*zx::unowned_handle{task.get()}, Topic, std::move(data_));
    if (result.is_error()) {
      return result.take_error();
    }
    data_ = std::move(result).value();
    this->Emplace({
        reinterpret_cast<const std::byte*>(data_.data()),
        data_.size() * sizeof(data_[0]),
    });
    return fitx::ok();
  }

  cpp20::span<const T> info() const {
    static_assert(sizeof(T) == sizeof(data_.data()[0]));
    return {reinterpret_cast<const T*>(data_.data()), data_.size()};
  }

 private:
  InfoVector<T> data_;
};

// Notes based on the fixed-sized property/state calls use this.
template <typename Class, uint32_t Prop, typename T>
class PropertyNote : public NoteBase<Class, Prop> {
 public:
  fitx::result<Error> Collect(const typename Class::Handle& handle) {
    zx_status_t status = (handle.*Class::kSyscall)(Prop, &data_, sizeof(T));
    if (status != ZX_OK) {
      return fitx::error(Error{Class::kCall_, status});
    }
    this->Emplace({reinterpret_cast<std::byte*>(&data_), sizeof(data_)});
    return fitx::ok();
  }

 private:
  T data_;
};

// Classes using zx_object_get_property use this.
struct PropertyBaseClass {
  static constexpr std::string_view kCall_{"zx_object_get_property"};
  static constexpr auto kSyscall = &zx::object_base::get_property;
};

// These are called via std::apply on ProcessNotes tuples.

constexpr auto CollectNoteData =
    // For each note that hasn't already been fetched, try to fetch it now.
    [](const auto& handle, auto&... note) -> fitx::result<Error, size_t> {
  // This value is always replaced (or ignored), but the type is not
  // default-constructible.
  fitx::result<Error> result = fitx::ok();

  size_t total = 0;
  auto collect = [&handle, &result, &total](auto& note) -> bool {
    result = CollectNote(handle, note);
    if (result.is_ok()) {
      total += note.size_bytes();
      return true;
    }
    switch (result.error_value().status_) {
      case ZX_ERR_NOT_SUPPORTED:
      case ZX_ERR_BAD_STATE:
        // These just mean the data is not available because it never
        // existed or the thread is dead.
        return true;

      default:
        return false;
    }
  };

  if (!(collect(note) && ...)) {
    // The fold expression bailed out early after setting result.
    return result.take_error();
  }

  return fitx::ok(total);
};

constexpr auto DumpNoteData =
    // Return a vector pointing at all the nonempty note data.
    [](const auto&... note) -> NoteData::Vector {
  NoteData data;
  (note.AddToNoteData(data), ...);
  return std::move(data).take();
};

}  // namespace

// The public class is just a container for a std::unique_ptr to this private
// class, so no implementation details of the object need to be visible in the
// public header.
class ProcessDumpBase::Collector {
 public:
  // Only constructed by Emplace.
  Collector() = delete;

  // Only Emplace and clear call this.  The process is mandatory and all other
  // members are safely default-initialized.
  explicit Collector(zx::unowned_process process) : process_(std::move(process)) {
    ZX_ASSERT(process_->is_valid());
  }

  // Reset to initial state.
  void clear() { *this = Collector{std::move(process_)}; }

  // This collects information and other process-wide state.  The return value
  // gives the total size of the ET_CORE file to be written.  Collection is cut
  // short without error if the ET_CORE file would already exceed the size
  // limit without even including the memory.
  fitx::result<Error, size_t> CollectProcess(size_t limit) {
    // Collect the process-wide note data.
    auto collect = [this](auto&... note) -> fitx::result<Error, size_t> {
      return CollectNoteData(*process_, note...);
    };
    if (auto result = std::apply(collect, notes_); result.is_error()) {
      return result.take_error();
    } else {
      notes_size_bytes_ += result.value();
    }

    // Clear out from any previous use.
    phdrs_.clear();

    // The first phdr is the main note segment.
    const Elf::Phdr note_phdr = {
        .type = elfldltl::ElfPhdrType::kNote,
        .flags = Elf::Phdr::kRead,
        .filesz = notes_size_bytes_,
        .align = NoteAlign(),
    };
    phdrs_.push_back(note_phdr);

    // Now figure everything else out to write out a full ET_CORE file.
    return fitx::ok(Layout());
  }

  // Accumulate header and note data to be written out, by calling
  // `dump(offset, ByreView{...})` repeatedly.
  // The views point to storage in this->notes and Thread::notes_.
  size_t DumpHeaders(DumpCallback dump, size_t limit) {
    // Layout has already been done.
    ZX_ASSERT(ehdr_.type == elfldltl::ElfType::kCore);

    size_t offset = 0;
    auto append = [&](ByteView data) -> bool {
      if (offset >= limit || limit - offset < data.size()) {
        return false;
      }
      bool bail = dump(offset, data);
      offset += data.size();
      return bail;
    };

    // Generate the ELF headers.
    if (append({reinterpret_cast<std::byte*>(&ehdr_), sizeof(ehdr_)})) {
      return offset;
    }
    if (ehdr_.shnum > 0) {
      ZX_DEBUG_ASSERT(ehdr_.shnum() == 1);
      ZX_DEBUG_ASSERT(ehdr_.shoff == offset);
      if (append({reinterpret_cast<std::byte*>(&shdr_), sizeof(shdr_)})) {
        return offset;
      }
    }
    if (append({reinterpret_cast<std::byte*>(phdrs_.data()), phdrs_.size() * sizeof(phdrs_[0])})) {
      return offset;
    }

    // Generate the process-wide note data.
    for (ByteView data : notes()) {
      if (append(data)) {
        return offset;
      }
    }

    ZX_DEBUG_ASSERT(offset % NoteAlign() == 0);
    return offset;
  }

 private:
  struct ProcessInfoClass {
    using Handle = zx::process;
    static constexpr auto MakeHeader = kMakeNote<kProcessInfoNoteName>;
  };

  template <zx_object_info_topic_t Topic, typename T>
  using ProcessInfo = InfoNote<ProcessInfoClass, Topic, T>;

  struct ProcessPropertyClass : public PropertyBaseClass {
    using Handle = zx::process;
    static constexpr auto MakeHeader = kMakeNote<kProcessPropertyNoteName>;
  };

  template <uint32_t Prop, typename T>
  using ProcessProperty = PropertyNote<ProcessPropertyClass, Prop, T>;

  using ProcessNotes = std::tuple<
      // This lists all the notes for process-wide state.  Ordering of the
      // notes after the first two is not specified and can change.
      ProcessInfo<ZX_INFO_HANDLE_BASIC, zx_info_handle_basic_t>,
      ProcessProperty<ZX_PROP_NAME, char[ZX_MAX_NAME_LEN]>,
      ProcessInfo<ZX_INFO_PROCESS, zx_info_process_t>,
      ProcessInfo<ZX_INFO_PROCESS_THREADS, zx_koid_t>,
      ProcessInfo<ZX_INFO_TASK_STATS, zx_info_task_stats_t>,
      ProcessInfo<ZX_INFO_TASK_RUNTIME, zx_info_task_runtime_t>,
      ProcessInfo<ZX_INFO_PROCESS_MAPS, zx_info_maps_t>,
      ProcessInfo<ZX_INFO_PROCESS_VMOS, zx_info_vmo_t>,
      ProcessInfo<ZX_INFO_PROCESS_HANDLE_STATS, zx_info_process_handle_stats_t>,
      ProcessInfo<ZX_INFO_HANDLE_TABLE, zx_info_handle_extended_t>,
      ProcessProperty<ZX_PROP_PROCESS_DEBUG_ADDR, uintptr_t>,
      ProcessProperty<ZX_PROP_PROCESS_BREAK_ON_LOAD, uintptr_t>,
      ProcessProperty<ZX_PROP_PROCESS_VDSO_BASE_ADDRESS, uintptr_t>,
      ProcessProperty<ZX_PROP_PROCESS_HW_TRACE_CONTEXT_ID, uintptr_t>>;

  // Returns a vector of views into the storage held in this->notes_.
  NoteData::Vector notes() const { return std::apply(DumpNoteData, notes_); }

  // Some of the process-wide state is needed in Suspend anyway, so pre-collect
  // it directly in the notes.

  auto& process_threads() {
    return std::get<ProcessInfo<ZX_INFO_PROCESS_THREADS, zx_koid_t>>(notes_);
  }

  auto& process_maps() {
    return std::get<ProcessInfo<ZX_INFO_PROCESS_MAPS, zx_info_maps_t>>(notes_);
  }

  auto& process_vmos() {
    return std::get<ProcessInfo<ZX_INFO_PROCESS_VMOS, zx_info_vmo_t>>(notes_);
  }

  // Populate the header fields and reify phdrs_ with p_offset values.
  // This chooses where everything will go in the ET_CORE file.
  size_t Layout() {
    // Fill in the file header boilerplate.
    ehdr_.magic = Elf::Ehdr::kMagic;
    ehdr_.elfclass = elfldltl::ElfClass::k64;
    ehdr_.elfdata = elfldltl::ElfData::k2Lsb;
    ehdr_.ident_version = elfldltl::ElfVersion::kCurrent;
    ehdr_.type = elfldltl::ElfType::kCore;
    ehdr_.machine = elfldltl::ElfMachine::kNative;
    ehdr_.version = elfldltl::ElfVersion::kCurrent;
    size_t offset = ehdr_.phoff = ehdr_.ehsize = sizeof(ehdr_);
    ehdr_.phentsize = sizeof(phdrs_[0]);
    offset += phdrs_.size() * sizeof(phdrs_[0]);
    if (phdrs_.size() < Elf::Ehdr::kPnXnum) {
      ehdr_.phnum = static_cast<uint16_t>(phdrs_.size());
    } else {
      shdr_.info = static_cast<uint32_t>(phdrs_.size());
      ehdr_.phnum = Elf::Ehdr::kPnXnum;
      ehdr_.shnum = 1;
      ehdr_.shentsize = sizeof(shdr_);
      ehdr_.shoff = offset;
      offset += sizeof(shdr_);
    }

    // Now assign offsets to all the segments.
    auto place = [&offset](Elf::Phdr& phdr) {
      if (phdr.filesz == 0) {
        phdr.offset = 0;
      } else {
        offset = (offset + phdr.align - 1) & -size_t{phdr.align};
        phdr.offset = offset;
        offset += phdr.filesz;
      }
    };

    ZX_DEBUG_ASSERT(phdrs_.size() == 1);

    // First is the initial note segment.
    ZX_DEBUG_ASSERT(phdrs_[0].type == elfldltl::ElfPhdrType::kNote);
    place(phdrs_[0]);

    ZX_DEBUG_ASSERT(offset % NoteAlign() == 0);
    return offset;
  }

  zx::unowned_process process_;
  zx::suspend_token process_suspended_;
  ProcessNotes notes_;

  std::vector<Elf::Phdr> phdrs_;
  Elf::Ehdr ehdr_ = {};
  Elf::Shdr shdr_ = {};  // Only used for the PN_XNUM case.

  // This collects the totals for process-wide notes.
  size_t notes_size_bytes_ = 0;
};

ProcessDumpBase::~ProcessDumpBase() = default;

void ProcessDumpBase::clear() { collector_->clear(); }

fitx::result<Error, size_t> ProcessDumpBase::CollectProcess(size_t limit) {
  return collector_->CollectProcess(limit);
}

size_t ProcessDumpBase::DumpHeadersImpl(DumpCallback dump, size_t limit) {
  return collector_->DumpHeaders(std::move(dump), limit);
}

// The Collector borrows the process handle.  A single Collector cannot be
// used for a different process later.  It can be clear()'d to reset all
// state other than the process handle.
void ProcessDumpBase::Emplace(zx::unowned_process process) {
  collector_ = std::make_unique<Collector>(std::move(process));
}

template <>
ProcessDump<zx::process>::ProcessDump(zx::process process) noexcept : process_{std::move(process)} {
  Emplace(zx::unowned_process{process_});
}

template class ProcessDump<zx::unowned_process>;

template <>
ProcessDump<zx::unowned_process>::ProcessDump(zx::unowned_process process) noexcept
    : process_{std::move(process)} {
  Emplace(zx::unowned_process{process_});
}

}  // namespace zxdump