src/lib/elfldltl/test/get-test-lib.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 <fidl/fuchsia.ldsvc/cpp/wire.h>
#include <lib/fdio/fd.h>
#include <lib/zx/channel.h>
#include <zircon/dlfcn.h>
#include <zircon/status.h>

#include <cerrno>
#include <string_view>

#include <fbl/unique_fd.h>
#include <gtest/gtest.h>

// The fdio open doesn't support getting an fd that will allow PROT_EXEC mmap
// usage, i.e. yield a VMO with ZX_RIGHT_EXECUTE.  Instead, use the loader
// service to look up the file in /pkg/lib. Note this uses gtest assertions for all
// failures and so must be used inside a gtest TEST(...) function.
zx::vmo GetTestLibVmo(std::string_view libname) {
  constexpr auto init_ldsvc = []() {
    // The dl_set_loader_service API replaces the handle used by `dlopen` et al
    // and returns the old one, so initialize by borrowing that handle while
    // leaving it intact in the system runtime.
    zx::unowned_channel channel{dl_set_loader_service(ZX_HANDLE_INVALID)};
    EXPECT_TRUE(channel->is_valid());
    zx_handle_t reset = dl_set_loader_service(channel->get());
    EXPECT_EQ(reset, ZX_HANDLE_INVALID);
    return fidl::UnownedClientEnd<fuchsia_ldsvc::Loader>{channel};
  };
  static const auto ldsvc_endpoint = init_ldsvc();

  fidl::Arena arena;
  fidl::WireResult result =
      fidl::WireCall<fuchsia_ldsvc::Loader>(ldsvc_endpoint)->LoadObject({arena, libname});
  EXPECT_TRUE(result.ok()) << libname << ": " << zx_status_get_string(result.status());
  if (!result.ok()) {
    return {};
  }
  EXPECT_EQ(result->rv, ZX_OK) << libname << ": " << zx_status_get_string(result->rv);
  if (result->rv != ZX_OK) {
    return {};
  }
  return std::move(result->object);
}

// Fuchsia-specific implementation of GetTestLib; a custom implementation is needed
// because fdio open does not support returning an executable fd.
fbl::unique_fd GetTestLib(std::string_view libname) {
  zx::vmo lib_vmo = GetTestLibVmo(libname);
  int fd;
  zx_status_t status = fdio_fd_create(lib_vmo.release(), &fd);
  EXPECT_EQ(status, ZX_OK) << libname << ": fdio_fd_create: " << zx_status_get_string(status);

  return fbl::unique_fd{fd};
}