wasmer/lib/llvm-backend/cpp/object_loader.cpp

#include "object_loader.hh"
#include <iostream>
#include <memory>

extern "C" void __register_frame(uint8_t *);
extern "C" void __deregister_frame(uint8_t *);

struct UnwindPoint {
    UnwindPoint *prev;
    jmp_buf unwind_info;
    std::unique_ptr<std::exception> exception;
};

static thread_local UnwindPoint *unwind_state = nullptr;

void catch_unwind(std::function<void()>&& f) {
    UnwindPoint current;
    current.prev = unwind_state;
    unwind_state = &current;

    bool rethrow = false;

    if(setjmp(current.unwind_info)) {
        rethrow = true;
    } else {
        f();
    }

    unwind_state = current.prev;
    if(rethrow) throw *current.exception;
}

void unsafe_unwind(std::exception *exception) {
    UnwindPoint *state = unwind_state;
    if(state) {
        state->exception.reset(exception);
        longjmp(state->unwind_info, 42);
    } else {
        abort();
    }
}

struct MemoryManager : llvm::RuntimeDyld::MemoryManager {
public:
  MemoryManager(callbacks_t callbacks) : callbacks(callbacks) {}

  virtual ~MemoryManager() override {
    deregisterEHFrames();
    // Deallocate all of the allocated memory.
    callbacks.dealloc_memory(code_section.base, code_section.size);
    callbacks.dealloc_memory(read_section.base, read_section.size);
    callbacks.dealloc_memory(readwrite_section.base, readwrite_section.size);
  }

  virtual uint8_t *allocateCodeSection(uintptr_t size, unsigned alignment,
                                       unsigned section_id,
                                       llvm::StringRef section_name) override {
    return allocate_bump(code_section, code_bump_ptr, size, alignment);
  }

  virtual uint8_t *allocateDataSection(uintptr_t size, unsigned alignment,
                                       unsigned section_id,
                                       llvm::StringRef section_name,
                                       bool read_only) override {
    // Allocate from the read-only section or the read-write section, depending
    // on if this allocation should be read-only or not.
    if (read_only) {
      return allocate_bump(read_section, read_bump_ptr, size, alignment);
    } else {
      return allocate_bump(readwrite_section, readwrite_bump_ptr, size,
                           alignment);
    }
  }

  virtual void reserveAllocationSpace(uintptr_t code_size, uint32_t code_align,
                                      uintptr_t read_data_size,
                                      uint32_t read_data_align,
                                      uintptr_t read_write_data_size,
                                      uint32_t read_write_data_align) override {
    auto aligner = [](uintptr_t ptr, size_t align) {
      if (ptr == 0) {
        return align;
      }
      return (ptr + align - 1) & ~(align - 1);
    };

    uint8_t *code_ptr_out = nullptr;
    size_t code_size_out = 0;
    auto code_result =
        callbacks.alloc_memory(aligner(code_size, 4096), PROTECT_READ_WRITE,
                               &code_ptr_out, &code_size_out);
    assert(code_result == RESULT_OK);
    code_section = Section{code_ptr_out, code_size_out};
    code_bump_ptr = (uintptr_t)code_ptr_out;

    uint8_t *read_ptr_out = nullptr;
    size_t read_size_out = 0;
    auto read_result = callbacks.alloc_memory(aligner(read_data_size, 4096),
                                              PROTECT_READ_WRITE, &read_ptr_out,
                                              &read_size_out);
    assert(read_result == RESULT_OK);
    read_section = Section{read_ptr_out, read_size_out};
    read_bump_ptr = (uintptr_t)read_ptr_out;

    uint8_t *readwrite_ptr_out = nullptr;
    size_t readwrite_size_out = 0;
    auto readwrite_result = callbacks.alloc_memory(
        aligner(read_write_data_size, 4096), PROTECT_READ_WRITE,
        &readwrite_ptr_out, &readwrite_size_out);
    assert(readwrite_result == RESULT_OK);
    readwrite_section = Section{readwrite_ptr_out, readwrite_size_out};
    readwrite_bump_ptr = (uintptr_t)readwrite_ptr_out;
  }

  /* Turn on the `reserveAllocationSpace` callback. */
  virtual bool needsToReserveAllocationSpace() override { return true; }

  virtual void registerEHFrames(uint8_t *addr, uint64_t LoadAddr,
                                size_t size) override {
// We don't know yet how to do this on Windows, so we hide this on compilation
// so we can compile and pass spectests on unix systems
#ifndef _WIN32
    eh_frame_ptr = addr;
    eh_frame_size = size;
    eh_frames_registered = true;
    callbacks.visit_fde(addr, size, __register_frame);
#endif
  }

  virtual void deregisterEHFrames() override {
// We don't know yet how to do this on Windows, so we hide this on compilation
// so we can compile and pass spectests on unix systems
#ifndef _WIN32
    if (eh_frames_registered) {
      callbacks.visit_fde(eh_frame_ptr, eh_frame_size, __deregister_frame);
    }
#endif
  }

  virtual bool finalizeMemory(std::string *ErrMsg = nullptr) override {
    auto code_result =
        callbacks.protect_memory(code_section.base, code_section.size,
                                 mem_protect_t::PROTECT_READ_EXECUTE);
    if (code_result != RESULT_OK) {
      return false;
    }

    auto read_result = callbacks.protect_memory(
        read_section.base, read_section.size, mem_protect_t::PROTECT_READ);
    if (read_result != RESULT_OK) {
      return false;
    }

    // The readwrite section is already mapped as read-write.

    return false;
  }

  virtual void
  notifyObjectLoaded(llvm::RuntimeDyld &RTDyld,
                     const llvm::object::ObjectFile &Obj) override {}

private:
  struct Section {
    uint8_t *base;
    size_t size;
  };

  uint8_t *allocate_bump(Section &section, uintptr_t &bump_ptr, size_t size,
                         size_t align) {
    auto aligner = [](uintptr_t &ptr, size_t align) {
      ptr = (ptr + align - 1) & ~(align - 1);
    };

    // Align the bump pointer to the requires alignment.
    aligner(bump_ptr, align);

    auto ret_ptr = bump_ptr;
    bump_ptr += size;

    assert(bump_ptr <= (uintptr_t)section.base + section.size);

    return (uint8_t *)ret_ptr;
  }

  Section code_section, read_section, readwrite_section;
  uintptr_t code_bump_ptr, read_bump_ptr, readwrite_bump_ptr;
  uint8_t *eh_frame_ptr;
  size_t eh_frame_size;
  bool eh_frames_registered = false;

  callbacks_t callbacks;
};

struct SymbolLookup : llvm::JITSymbolResolver {
public:
  SymbolLookup(callbacks_t callbacks) : callbacks(callbacks) {}

  void lookup(const LookupSet &symbols, OnResolvedFunction OnResolved) {
    LookupResult result;

    for (auto symbol : symbols) {
      result.emplace(symbol, symbol_lookup(symbol));
    }

    OnResolved(result);
  }

  llvm::Expected<LookupSet> getResponsibilitySet(const LookupSet &Symbols) {
    const std::set<llvm::StringRef> empty;
    return empty;
  }

private:
  llvm::JITEvaluatedSymbol symbol_lookup(llvm::StringRef name) {
    uint64_t addr = callbacks.lookup_vm_symbol(name.data(), name.size());

    return llvm::JITEvaluatedSymbol(addr, llvm::JITSymbolFlags::None);
  }

  callbacks_t callbacks;
};

WasmModule::WasmModule(const uint8_t *object_start, size_t object_size,
                       callbacks_t callbacks)
    : memory_manager(
          std::unique_ptr<MemoryManager>(new MemoryManager(callbacks))) {

  if (auto created_object_file =
          llvm::object::ObjectFile::createObjectFile(llvm::MemoryBufferRef(
              llvm::StringRef((const char *)object_start, object_size),
              "object"))) {
    object_file = cantFail(std::move(created_object_file));
    SymbolLookup symbol_resolver(callbacks);
    runtime_dyld = std::unique_ptr<llvm::RuntimeDyld>(
        new llvm::RuntimeDyld(*memory_manager, symbol_resolver));

    runtime_dyld->setProcessAllSections(true);

    runtime_dyld->loadObject(*object_file);
    runtime_dyld->finalizeWithMemoryManagerLocking();

    if (runtime_dyld->hasError()) {
      _init_failed = true;
      return;
    }
  } else {
    _init_failed = true;
  }
}

void *WasmModule::get_func(llvm::StringRef name) const {
  auto symbol = runtime_dyld->getSymbol(name);
  return (void *)symbol.getAddress();
}