android: crazy-linker: Load from file descriptor and reserved mappings.

This CL extends the LoadParams struct to allow loading a library from
an existing file descriptor and/or a reserved memory mapping as well.

This will be used later to implement a wrapper for android_dlopen_ext()
that support ANDROID_DLEXT_{USE_LIBRARY_FD, USE_LIBRARY_FD_OFFSET,
RESERVED_ADDRESS, RESERVED_ADDRESS_HINT}.

+ Provide new tests to verify that the feature works properly.
+ Fix FileDescriptor move assignment operator for 64-bit unit tests.

BUG=936001
R=pasko@chromium.org, agrieve@chromium.org, cjgrant@chromium.org

Change-Id: I1ed174dfa268f780c5397f6e76c659f8fa57c935
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1564111
Commit-Queue: David Turner <digit@chromium.org>
Reviewed-by: Egor Pasko <pasko@chromium.org>
Reviewed-by: Andrew Grieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658519}

third_party/android_crazy_linker/BUILD.gn

@@ -33,8 +33,10 @@ if (is_android) {
       ":crazy_linker_test_jni_hooks",
       ":crazy_linker_test_load_library",
       ":crazy_linker_test_load_library_depends",
+      ":crazy_linker_test_load_library_with_fd",
       ":crazy_linker_test_load_library_with_gnu_hash_table",
       ":crazy_linker_test_load_library_with_relr_relocations",
+      ":crazy_linker_test_load_library_with_reserved_map",
       ":crazy_linker_test_relocated_shared_relro",
       ":crazy_linker_test_search_path_list",
       ":crazy_linker_test_shared_relro",
@@ -390,6 +392,30 @@ if (is_android) {
     ]
   }
 
+  executable("crazy_linker_test_load_library_with_fd") {
+    sources = [
+      "src/tests/test_load_library_with_fd.cpp",
+    ]
+    data_deps = [
+      ":crazy_linker_tests_libfoo",
+    ]
+    deps = [
+      ":android_crazy_linker",
+    ]
+  }
+
+  executable("crazy_linker_test_load_library_with_reserved_map") {
+    sources = [
+      "src/tests/test_load_library_with_reserved_map.cpp",
+    ]
+    data_deps = [
+      ":crazy_linker_tests_libfoo",
+    ]
+    deps = [
+      ":android_crazy_linker",
+    ]
+  }
+
   executable("crazy_linker_test_load_library_with_relr_relocations") {
     sources = [
       "src/tests/test_load_library.cpp",

third_party/android_crazy_linker/src/include/crazy_linker.h

@@ -82,6 +82,25 @@ void crazy_context_set_load_address(crazy_context_t* context,
 // Return the current load address in a context.
 size_t crazy_context_get_load_address(crazy_context_t* context) _CRAZY_PUBLIC;
 
+// Set the explicit library file descriptor in a context object. Values >= 0
+// will be used during the next crazy_library_open() call to read the library
+// file, instead of opening it using its path.
+void crazy_context_set_library_fd(crazy_context_t* context,
+                                  int fd) _CRAZY_PUBLIC;
+
+// Return the current library file descriptor in a context.
+int crazy_context_get_library_fd(crazy_context_t* context) _CRAZY_PUBLIC;
+
+// Set an explicit reserved memory mapping to be used on the next library
+// load. |reserved_address| is the page-aligned reserved address,
+// |reserved_size| is the page-aligned reserved size, and if |load_fallback|
+// is true, then the linker will try to load the library at a different
+// address if it fails to load its segments at the reserved address range.
+void crazy_context_set_reserved_map(crazy_context_t* context,
+                                    uintptr_t reserved_address,
+                                    size_t reserved_size,
+                                    bool load_fallback) _CRAZY_PUBLIC;
+
 // Destroy a given context object.
 void crazy_context_destroy(crazy_context_t* context) _CRAZY_PUBLIC;
 

third_party/android_crazy_linker/src/run_tests.sh

@@ -168,8 +168,10 @@ crazy_linker_test_dl_wrappers_valid_handles \
 crazy_linker_test_jni_hooks \
 crazy_linker_test_load_library \
 crazy_linker_test_load_library_depends \
+crazy_linker_test_load_library_with_fd \
 crazy_linker_test_load_library_with_gnu_hash_table \
 crazy_linker_test_load_library_with_relr_relocations \
+crazy_linker_test_load_library_with_reserved_map \
 crazy_linker_test_relocated_shared_relro \
 crazy_linker_test_search_path_list \
 crazy_linker_test_shared_relro \

third_party/android_crazy_linker/src/src/crazy_linker_api.cpp

@@ -32,6 +32,9 @@ using crazy::LibraryView;
 
 struct crazy_context_t {
   size_t load_address = 0;
+  int library_fd = -1;
+  size_t reserved_size = 0;
+  bool reserved_load_fallback = false;
   Error error;
 };
 
@@ -64,6 +67,23 @@ size_t crazy_context_get_load_address(crazy_context_t* context) {
   return context->load_address;
 }
 
+void crazy_context_set_library_fd(crazy_context_t* context, int fd) {
+  context->library_fd = fd;
+}
+
+int crazy_context_get_library_fd(crazy_context_t* context) {
+  return context->library_fd;
+}
+
+void crazy_context_set_reserved_map(crazy_context_t* context,
+                                    uintptr_t reserved_address,
+                                    size_t reserved_size,
+                                    bool load_fallback) {
+  context->load_address = reserved_address;
+  context->reserved_size = reserved_size;
+  context->reserved_load_fallback = load_fallback;
+}
+
 void crazy_context_destroy(crazy_context_t* context) {
   delete context;
 }
@@ -112,6 +132,8 @@ crazy_status_t crazy_library_open(crazy_library_t** library,
   crazy::LibraryList* libs = globals->libraries();
   crazy::LoadParams params;
   params.wanted_address = context->load_address;
+  params.reserved_size = context->reserved_size;
+  params.reserved_load_fallback = context->reserved_load_fallback;
   crazy::Expected<LibraryView*> found =
       libs->FindAndCheckLoadedLibrary(lib_name, params, &context->error);
   if (!found.has_value())
@@ -119,11 +141,22 @@ crazy_status_t crazy_library_open(crazy_library_t** library,
 
   LibraryView* view = found.value();
   if (!view) {
-    if (!libs->LocateLibraryFile(lib_name, *globals->search_path_list(),
-                                 &params, &context->error)) {
-      return CRAZY_STATUS_FAILURE;
+    if (context->library_fd >= 0) {
+      params.library_path = lib_name;
+      params.library_fd = context->library_fd;
+    } else {
+      if (!libs->LocateLibraryFile(lib_name, *globals->search_path_list(),
+                                   &params, &context->error)) {
+        return CRAZY_STATUS_FAILURE;
+      }
     }
     view = libs->LoadLibraryInternal(params, &context->error);
+
+    // Cleanup context.
+    context->library_fd = -1;
+    context->load_address = 0;
+    context->reserved_size = 0;
+    context->reserved_load_fallback = false;
   }
 
   if (!view)

third_party/android_crazy_linker/src/src/crazy_linker_elf_loader.cpp

@@ -23,6 +23,31 @@ namespace crazy {
 
 namespace {
 
+// A FileDescriptor sub-class that can also avoid closing the descriptor
+// on scope exit if DontCloseOnExit() is called.
+class LibraryFd : public FileDescriptor {
+ public:
+  LibraryFd() = default;
+
+  explicit LibraryFd(int fd) : FileDescriptor(fd) {}
+
+  explicit LibraryFd(const char* path) : FileDescriptor(path) {}
+
+  ~LibraryFd() {
+    if (!close_on_exit_)
+      Release();
+  }
+
+  LibraryFd(LibraryFd&& other) = default;
+  LibraryFd& operator=(LibraryFd&& other) = default;
+
+  // Ensure the file descriptor is not closed in the destructor.
+  void DontCloseOnExit() { close_on_exit_ = false; }
+
+ private:
+  bool close_on_exit_ = true;
+};
+
 class InternalElfLoader {
  public:
   ~InternalElfLoader();
@@ -42,7 +67,7 @@ class InternalElfLoader {
   MemoryMapping ReleaseMapping() { return std::move(reserved_map_); }
 
  private:
-  FileDescriptor fd_;
+  LibraryFd fd_;
   const char* path_ = nullptr;
 
   ELF::Ehdr header_ = {};
@@ -82,8 +107,12 @@ InternalElfLoader::~InternalElfLoader() {
 
 bool InternalElfLoader::LoadAt(const LoadParams& params, Error* error) {
   const char* lib_path = params.library_path.c_str();
-  LOG("lib_path='%s', file_offset=%p, load_address=%lx", lib_path,
-      params.library_offset, static_cast<unsigned long>(params.wanted_address));
+  LOG("lib_path='%s', file_fd=%d, file_offset=%p, load_address=%lx"
+      "reserved_size=%lx reserved_load_fallback=%s",
+      lib_path, params.library_fd, params.library_offset,
+      static_cast<unsigned long>(params.wanted_address),
+      static_cast<unsigned long>(params.reserved_size),
+      params.reserved_load_fallback ? "true" : "false");
 
   // Check that the load address is properly page-aligned.
   uintptr_t wanted_address = params.wanted_address;
@@ -92,6 +121,19 @@ bool InternalElfLoader::LoadAt(const LoadParams& params, Error* error) {
     return false;
   }
 
+  if (params.reserved_size != 0) {
+    if (!wanted_address) {
+      error->Format("Reserved size 0x%08lx has not reserved address",
+                    static_cast<unsigned long>(params.reserved_size));
+      return false;
+    }
+    if (params.reserved_size != PAGE_START(params.reserved_size)) {
+      error->Format("Reserved size 0x%08lx is not page-aligned",
+                    static_cast<unsigned long>(params.reserved_size));
+      return false;
+    }
+  }
+
   // Check that the file offset is also properly page-aligned.
   // PAGE_START() can't be used here due to the compiler complaining about
   // comparing signed (off_t) and unsigned (size_t) values.
@@ -104,9 +146,14 @@ bool InternalElfLoader::LoadAt(const LoadParams& params, Error* error) {
   file_offset_ = file_offset;
 
   // Open the file.
-  if (!fd_.OpenReadOnly(lib_path)) {
-    error->Format("Can't open file: %s", strerror(errno));
-    return false;
+  if (params.library_fd >= 0) {
+    fd_ = LibraryFd(params.library_fd);
+    fd_.DontCloseOnExit();
+  } else {
+    if (!fd_.OpenReadOnly(lib_path)) {
+      error->Format("Can't open file: %s", strerror(errno));
+      return false;
+    }
   }
 
   if (file_offset && fd_.SeekTo(file_offset) < 0) {
@@ -122,13 +169,25 @@ bool InternalElfLoader::LoadAt(const LoadParams& params, Error* error) {
     return false;
   }
 
-  if (!LoadSegments(error) || !FindPhdr(error)) {
-    // An error occured, cleanup the address space by un-mapping the
-    // range that was reserved by ReserveAddressSpace().
+  bool success = LoadSegments(error);
+  if (!success) {
+    // If loading the segments fail, but |reserved_size| was not 0, and
+    // |reserved_size_load_fallback| is true, then try again at a not-fixed
+    // address.
+    if (params.reserved_size > 0 && params.reserved_load_fallback) {
+      LOG("Loading to reserved mapping failed, falling back to random one");
+      LoadParams params2 = params;
+      params2.wanted_address = 0;
+      params2.reserved_size = 0;
+      params2.reserved_load_fallback = false;
+      success = ReserveAddressSpace(params2, error) && LoadSegments(error);
+    }
+  }
+  success = success && FindPhdr(error);
+  if (!success) {
     reserved_map_.Deallocate();
     return false;
   }
-
   return true;
 }
 
@@ -235,27 +294,38 @@ bool InternalElfLoader::ReserveAddressSpace(const LoadParams& params,
     mmap_flags |= MAP_FIXED;
   }
 
-  size_t reserved_size = load_size_;
-
-  LOG("Trying to reserve memory address=%p size=%lu (0x%lx)", addr,
-      static_cast<unsigned long>(load_size_),
-      static_cast<unsigned long>(load_size_));
-
-  void* start = mmap(addr, reserved_size, PROT_NONE, mmap_flags, -1, 0);
-  if (start == MAP_FAILED) {
-    error->Format("Could not reserve %lu bytes of address space",
-                  static_cast<unsigned long>(reserved_size));
-    return false;
-  }
-  if (addr && start != addr) {
-    error->Format("Could not map at %p requested, backing out", addr);
-    munmap(start, reserved_size);
+  void* start = reinterpret_cast<void*>(params.wanted_address);
+  size_t reserved_size = params.reserved_size;
+
+  if (!reserved_size) {
+    // Reserve the area ourselves.
+    reserved_size = load_size_;
+    LOG("Trying to reserve memory address=%p size=%lu (0x%lx)", addr,
+        static_cast<unsigned long>(load_size_),
+        static_cast<unsigned long>(load_size_));
+
+    start = mmap(addr, reserved_size, PROT_NONE, mmap_flags, -1, 0);
+    if (start == MAP_FAILED) {
+      error->Format("Could not reserve %lu bytes of address space",
+                    static_cast<unsigned long>(reserved_size));
+      return false;
+    }
+    if (addr && start != addr) {
+      error->Format("Could not map at %p requested, backing out", addr);
+      munmap(start, reserved_size);
+      return false;
+    }
+    // Take ownership of the mapping here.
+    reserved_map_ = MemoryMapping(start, reserved_size);
+  } else if (reserved_size < load_size_) {
+    error->Format("Reserved map size is too small 0x%lx (0x%lx required)",
+                  static_cast<unsigned long>(reserved_size),
+                  static_cast<unsigned long>(load_size_));
     return false;
+  } else {
+    LOG("Using client-allocated mapping!");
   }
 
-  // Take ownership of the mapping here.
-  reserved_map_ = MemoryMapping(start, reserved_size);
-
   load_start_ = start;
   load_bias_ = reinterpret_cast<ELF::Addr>(load_start_) - min_vaddr;
 

third_party/android_crazy_linker/src/src/crazy_linker_library_list.cpp

@@ -63,6 +63,11 @@ bool CheckSystemLibraryLoadParams(const char* lib_name,
   if (!lib_name)
     lib_name = params.library_path.c_str();
 
+  if (params.library_fd >= 0) {
+    error->Format("Cannot load system library from fd %d: %s",
+                  params.library_fd, lib_name);
+    return false;
+  }
   if (params.library_offset != 0) {
     error->Format("Cannot load system library from offset 0x%08lx: %s",
                   static_cast<unsigned long>(params.library_offset), lib_name);
@@ -73,6 +78,10 @@ bool CheckSystemLibraryLoadParams(const char* lib_name,
                   static_cast<unsigned long>(params.wanted_address), lib_name);
     return false;
   }
+  if (params.reserved_size != 0) {
+    error->Format("Cannot load system library in reserved memory map: %s",
+                  lib_name);
+  }
   return true;
 }
 

third_party/android_crazy_linker/src/src/crazy_linker_load_params.h

@@ -17,14 +17,24 @@ namespace crazy {
 // into the current process' address space.
 //
 // |library_path| is either the full library path.
+// |library_fd| is a file descriptor. If >= 0, the |library_path| is ignored.
 // |library_offset| is the page-aligned offset where the library starts in
-// its input file (typically > 0 when reading from Android APKs).
+//   its input file (typically > 0 when reading from Android APKs).
 // |wanted_address| is either 0, or the address where the library should
-// be loaded.
+//   be loaded.
+// |reserved_size| is either 0, or a page-aligned size in bytes corresponding
+//   to a reserved memory area where to load the library, starting from
+//   |wanted_address|.
+// |reserved_load_fallback| is ignored if |reserved_size| is 0. Otherwise, a
+//   value of true means that if the load fails at the reserved address range,
+//   the linker will try again at a different address.
 struct LoadParams {
   String library_path;
+  int library_fd = -1;
   off_t library_offset = 0;
   uintptr_t wanted_address = 0;
+  uintptr_t reserved_size = 0;
+  bool reserved_load_fallback = false;
 };
 
 }  // namespace crazy

third_party/android_crazy_linker/src/src/crazy_linker_shared_library.cpp

@@ -229,16 +229,19 @@ SharedLibrary::~SharedLibrary() = default;
 bool SharedLibrary::Load(const LoadParams& params, Error* error) {
   // First, record the path.
   const char* full_path = params.library_path.c_str();
-  LOG("full path '%s'", full_path);
-
-  size_t full_path_len = strlen(full_path);
-  if (full_path_len >= sizeof(full_path_)) {
-    error->Format("Path too long: %s", full_path);
-    return false;
+  if (params.library_fd >= 0) {
+    snprintf(full_path_, sizeof(full_path_), "fd(%d):%s", params.library_fd,
+             full_path);
+  } else {
+    size_t full_path_len = strlen(full_path);
+    if (full_path_len >= sizeof(full_path_)) {
+      error->Format("Path too long: %s", full_path);
+      return false;
+    }
+    strlcpy(full_path_, full_path, sizeof(full_path_));
   }
-
-  strlcpy(full_path_, full_path, sizeof(full_path_));
   base_name_ = GetBaseNamePtr(full_path_);
+  LOG("full path '%s'", full_path_);
 
   // Default value of |soname_| will be |base_name_| unless overidden
   // by a DT_SONAME entry. This helps deal with broken libraries that don't
@@ -263,6 +266,9 @@ bool SharedLibrary::Load(const LoadParams& params, Error* error) {
     }
 
     reserved_map_ = std::move(ret.reserved_mapping);
+
+    LOG("Reserved mapping %p size=0x%lx", reserved_map_.address(),
+        static_cast<unsigned long>(reserved_map_.size()));
   }
 
   if (phdr_table_get_relro_info(view_.phdr(),

third_party/android_crazy_linker/src/src/crazy_linker_system.cpp

@@ -77,12 +77,6 @@ bool IsSystemLibraryPath(const char* lib_path) {
   return false;
 }
 
-}  // namespace crazy
-
-#ifndef UNIT_TEST
-
-namespace crazy {
-
 FileDescriptor& FileDescriptor::operator=(FileDescriptor&& other) noexcept {
   if (this != &other) {
     if (fd_ != kEmptyFD) {
@@ -94,6 +88,12 @@ FileDescriptor& FileDescriptor::operator=(FileDescriptor&& other) noexcept {
   return *this;
 }
 
+}  // namespace crazy
+
+#ifndef UNIT_TEST
+
+namespace crazy {
+
 ssize_t FileDescriptor::Read(void* buffer, size_t buffer_size) {
   return TEMP_FAILURE_RETRY(::read(fd_, buffer, buffer_size));
 }

third_party/android_crazy_linker/src/tests/test_load_library_with_fd.cpp

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// A crazy linker test to:
+// - Load a library (libfoo.so) with the linker.
+// - Find the address of the "Foo" function in it.
+// - Call the function.
+// - Close the library.
+#include <crazy_linker.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <string>
+
+#include "test_util.h"
+
+typedef void (*FunctionPtr)();
+
+#ifndef LIB_NAME
+#define LIB_NAME "libcrazy_linker_tests_libfoo.so"
+#endif
+
+std::string GetProgramDirectory(const char* argv0) {
+  const char* sep = strrchr(argv0, '/');
+  if (!sep) {
+    return ".";
+  }
+  return std::string(argv0, sep - argv0);
+}
+
+int main(int argc, const char** argv) {
+  crazy_context_t* context = crazy_context_create();
+  crazy_library_t* library;
+
+  // DEBUG
+  crazy_context_set_load_address(context, 0x20000000);
+
+  // Assume library file is in the same directory as this executable.
+  std::string program_dir = GetProgramDirectory(argv[0]);
+  std::string lib_path = program_dir + "/" LIB_NAME;
+  int fd = open(lib_path.c_str(), O_RDONLY | O_CLOEXEC);
+  if (fd < 0) {
+    Panic("Could not find library file %s: %s\n", LIB_NAME, strerror(errno));
+  }
+
+  crazy_context_set_library_fd(context, fd);
+
+  int context_fd = crazy_context_get_library_fd(context);
+  if (context_fd != fd)
+    Panic("Invalid context fd %d (expected %d)\n", context_fd, fd);
+
+  // Load libfoo.so
+  if (!crazy_library_open(&library, LIB_NAME, context)) {
+    Panic("Could not open library: %s\n", crazy_context_get_error(context));
+  }
+
+  // Find the "Foo" symbol.
+  FunctionPtr foo_func;
+  if (!crazy_library_find_symbol(library, "Foo",
+                                 reinterpret_cast<void**>(&foo_func))) {
+    Panic("Could not find 'Foo' in %s\n", LIB_NAME);
+  }
+
+  // Call it.
+  (*foo_func)();
+
+  // Close the library.
+  printf("Closing %s\n", LIB_NAME);
+  crazy_library_close(library);
+
+  // Check that the descriptor is not closed, by trying to read from it.
+  char header[4];
+  if (TEMP_FAILURE_RETRY(lseek(fd, 0, SEEK_SET)) < 0 ||
+      TEMP_FAILURE_RETRY(read(fd, header, 4)) < 0) {
+    Panic("Could not read from file descriptor after library close!: %s",
+          strerror(errno));
+  }
+  close(fd);
+
+  context_fd = crazy_context_get_library_fd(context);
+  if (context_fd != -1)
+    Panic("Invalid context fd after library load %d (expected -1)", context_fd);
+
+  crazy_context_destroy(context);
+  printf("OK\n");
+  return 0;
+}

third_party/android_crazy_linker/src/tests/test_load_library_with_reserved_map.cpp

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// A crazy linker test to:
+// - Load a library (libfoo.so) with the linker.
+// - Find the address of the "Foo" function in it.
+// - Call the function.
+// - Close the library.
+#include <crazy_linker.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <string>
+
+#include "test_util.h"
+
+typedef void (*FunctionPtr)();
+
+#ifndef LIB_NAME
+#define LIB_NAME "libcrazy_linker_tests_libfoo.so"
+#endif
+
+std::string GetProgramDirectory(const char* argv0) {
+  const char* sep = strrchr(argv0, '/');
+  if (!sep) {
+    return ".";
+  }
+  return std::string(argv0, sep - argv0);
+}
+
+int main(int argc, const char** argv) {
+  crazy_context_t* context = crazy_context_create();
+  crazy_library_t* library;
+
+  // Allocate a memory map range large enough for our library.
+  const size_t kMapSize = 1024 * 1024;  // 1 MiB should be enough.
+  void* reserved_map =
+      mmap(nullptr, kMapSize, PROT_READ | PROT_WRITE | PROT_EXEC,
+           MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (reserved_map == MAP_FAILED)
+    Panic("mmap() failed: %s", strerror(errno));
+
+  crazy_context_set_reserved_map(
+      context, reinterpret_cast<uintptr_t>(reserved_map), kMapSize, false);
+
+  // Load libfoo.so
+  if (!crazy_library_open(&library, LIB_NAME, context)) {
+    Panic("Could not open library: %s\n", crazy_context_get_error(context));
+  }
+
+  // Find the "Foo" symbol.
+  FunctionPtr foo_func;
+  if (!crazy_library_find_symbol(library, "Foo",
+                                 reinterpret_cast<void**>(&foo_func))) {
+    Panic("Could not find 'Foo' in %s\n", LIB_NAME);
+  }
+
+  // Call it.
+  (*foo_func)();
+
+  // Close the library.
+  printf("Closing %s\n", LIB_NAME);
+  crazy_library_close(library);
+
+  // Check that the memory map is still there by writing to it.
+  printf("Erasing memory map\n");
+  if (mprotect(reserved_map, kMapSize, PROT_WRITE) < 0)
+    Panic("Could not mprotect() range: %s", strerror(errno));
+  memset(reserved_map, 1, kMapSize);
+
+  printf("Trying to reload inside smaller reserved map (no fallback).\n");
+  // Try to load the library again at the same address, without a reserved
+  // size. This should fail.
+  crazy_context_set_reserved_map(
+      context, reinterpret_cast<uintptr_t>(reserved_map), 4096, false);
+
+  if (crazy_library_open(&library, LIB_NAME, context)) {
+    Panic("Could unexpectedly load library in small mapping!");
+  }
+
+  printf("Trying to reload inside smaller reserved map (with fallback)\n.");
+  if (!crazy_library_open(&library, LIB_NAME, context)) {
+    Panic("Could not reload library with fallback in small mapping!");
+  }
+  crazy_library_close(library);
+
+  printf("Unmapping reserved mapping.\n");
+  if (munmap(reserved_map, kMapSize) < 0)
+    Panic("Could not unmap reserved mapping: %s", strerror(errno));
+
+  crazy_context_destroy(context);
+  printf("OK\n");
+  return 0;
+}