1 // Copyright 2014 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 // This is the Android-specific Chromium linker, a tiny shared library
6 // implementing a custom dynamic linker that can be used to load the
7 // real Chromium libraries (e.g. libcontentshell.so).
9 // The main point of this linker is to be able to share the RELRO
10 // section of libcontentshell.so (or equivalent) between the browser and
13 // This source code *cannot* depend on anything from base/ or the C++
14 // STL, to keep the final library small, and avoid ugly dependency issues.
16 #include <android/log.h>
17 #include <crazy_linker.h>
22 // Set this to 1 to enable debug traces to the Android log.
23 // Note that LOG() from "base/logging.h" cannot be used, since it is
24 // in base/ which hasn't been loaded yet.
27 #define TAG "chromium_android_linker"
30 #define LOG_INFO(...) __android_log_print(ANDROID_LOG_INFO, TAG, __VA_ARGS__)
32 #define LOG_INFO(...) ((void)0)
34 #define LOG_ERROR(...) __android_log_print(ANDROID_LOG_ERROR, TAG, __VA_ARGS__)
36 #define UNUSED __attribute__((unused))
40 // A simply scoped UTF String class that can be initialized from
41 // a Java jstring handle. Modeled like std::string, which cannot
45 String(JNIEnv
* env
, jstring str
);
52 const char* c_str() const { return ptr_
? ptr_
: ""; }
53 size_t size() const { return size_
; }
60 String::String(JNIEnv
* env
, jstring str
) {
61 size_
= env
->GetStringUTFLength(str
);
62 ptr_
= static_cast<char*>(::malloc(size_
+ 1));
64 // Note: the result contains Java "modified UTF-8" bytes.
65 // Good enough for the linker though.
66 const char* bytes
= env
->GetStringUTFChars(str
, NULL
);
67 ::memcpy(ptr_
, bytes
, size_
);
70 env
->ReleaseStringUTFChars(str
, bytes
);
73 // Return true iff |address| is a valid address for the target CPU.
74 bool IsValidAddress(jlong address
) {
75 return static_cast<jlong
>(static_cast<size_t>(address
)) == address
;
78 // Find the jclass JNI reference corresponding to a given |class_name|.
79 // |env| is the current JNI environment handle.
80 // On success, return true and set |*clazz|.
81 bool InitClassReference(JNIEnv
* env
, const char* class_name
, jclass
* clazz
) {
82 *clazz
= env
->FindClass(class_name
);
84 LOG_ERROR("Could not find class for %s", class_name
);
90 // Initialize a jfieldID corresponding to the field of a given |clazz|,
91 // with name |field_name| and signature |field_sig|.
92 // |env| is the current JNI environment handle.
93 // On success, return true and set |*field_id|.
94 bool InitFieldId(JNIEnv
* env
,
96 const char* field_name
,
97 const char* field_sig
,
99 *field_id
= env
->GetFieldID(clazz
, field_name
, field_sig
);
101 LOG_ERROR("Could not find ID for field '%s'", field_name
);
105 "%s: Found ID %p for field '%s'", __FUNCTION__
, *field_id
, field_name
);
109 // Initialize a jmethodID corresponding to the static method of a given
110 // |clazz|, with name |method_name| and signature |method_sig|.
111 // |env| is the current JNI environment handle.
112 // On success, return true and set |*method_id|.
113 bool InitStaticMethodId(JNIEnv
* env
,
115 const char* method_name
,
116 const char* method_sig
,
117 jmethodID
* method_id
) {
118 *method_id
= env
->GetStaticMethodID(clazz
, method_name
, method_sig
);
120 LOG_ERROR("Could not find ID for static method '%s'", method_name
);
123 LOG_INFO("%s: Found ID %p for static method '%s'",
124 __FUNCTION__
, *method_id
, method_name
);
128 // A class used to model the field IDs of the org.chromium.base.Linker
129 // LibInfo inner class, used to communicate data with the Java side
131 struct LibInfo_class
{
132 jfieldID load_address_id
;
133 jfieldID load_size_id
;
134 jfieldID relro_start_id
;
135 jfieldID relro_size_id
;
136 jfieldID relro_fd_id
;
138 // Initialize an instance.
139 bool Init(JNIEnv
* env
) {
141 if (!InitClassReference(
142 env
, "org/chromium/base/library_loader/Linker$LibInfo", &clazz
)) {
146 return InitFieldId(env
, clazz
, "mLoadAddress", "J", &load_address_id
) &&
147 InitFieldId(env
, clazz
, "mLoadSize", "J", &load_size_id
) &&
148 InitFieldId(env
, clazz
, "mRelroStart", "J", &relro_start_id
) &&
149 InitFieldId(env
, clazz
, "mRelroSize", "J", &relro_size_id
) &&
150 InitFieldId(env
, clazz
, "mRelroFd", "I", &relro_fd_id
);
153 void SetLoadInfo(JNIEnv
* env
,
154 jobject library_info_obj
,
157 env
->SetLongField(library_info_obj
, load_address_id
, load_address
);
158 env
->SetLongField(library_info_obj
, load_size_id
, load_size
);
161 // Use this instance to convert a RelroInfo reference into
162 // a crazy_library_info_t.
163 void GetRelroInfo(JNIEnv
* env
,
164 jobject library_info_obj
,
168 *relro_start
= static_cast<size_t>(
169 env
->GetLongField(library_info_obj
, relro_start_id
));
172 static_cast<size_t>(env
->GetLongField(library_info_obj
, relro_size_id
));
174 *relro_fd
= env
->GetIntField(library_info_obj
, relro_fd_id
);
177 void SetRelroInfo(JNIEnv
* env
,
178 jobject library_info_obj
,
182 env
->SetLongField(library_info_obj
, relro_start_id
, relro_start
);
183 env
->SetLongField(library_info_obj
, relro_size_id
, relro_size
);
184 env
->SetIntField(library_info_obj
, relro_fd_id
, relro_fd
);
188 static LibInfo_class s_lib_info_fields
;
190 // The linker uses a single crazy_context_t object created on demand.
191 // There is no need to protect this against concurrent access, locking
192 // is already handled on the Java side.
193 static crazy_context_t
* s_crazy_context
;
195 crazy_context_t
* GetCrazyContext() {
196 if (!s_crazy_context
) {
197 // Create new context.
198 s_crazy_context
= crazy_context_create();
200 // Ensure libraries located in the same directory as the linker
201 // can be loaded before system ones.
202 crazy_context_add_search_path_for_address(
203 s_crazy_context
, reinterpret_cast<void*>(&s_crazy_context
));
206 return s_crazy_context
;
209 // A scoped crazy_library_t that automatically closes the handle
210 // on scope exit, unless Release() has been called.
211 class ScopedLibrary
{
213 ScopedLibrary() : lib_(NULL
) {}
217 crazy_library_close_with_context(lib_
, GetCrazyContext());
220 crazy_library_t
* Get() { return lib_
; }
222 crazy_library_t
** GetPtr() { return &lib_
; }
224 crazy_library_t
* Release() {
225 crazy_library_t
* ret
= lib_
;
231 crazy_library_t
* lib_
;
236 template <class LibraryOpener
>
237 bool GenericLoadLibrary(
239 const char* library_name
, jlong load_address
, jobject lib_info_obj
,
240 const LibraryOpener
& opener
) {
241 crazy_context_t
* context
= GetCrazyContext();
243 if (!IsValidAddress(load_address
)) {
244 LOG_ERROR("%s: Invalid address 0x%llx", __FUNCTION__
, load_address
);
248 // Set the desired load address (0 means randomize it).
249 crazy_context_set_load_address(context
, static_cast<size_t>(load_address
));
251 ScopedLibrary library
;
252 if (!opener
.Open(library
.GetPtr(), library_name
, context
)) {
256 crazy_library_info_t info
;
257 if (!crazy_library_get_info(library
.Get(), context
, &info
)) {
258 LOG_ERROR("%s: Could not get library information for %s: %s",
261 crazy_context_get_error(context
));
265 // Release library object to keep it alive after the function returns.
268 s_lib_info_fields
.SetLoadInfo(
269 env
, lib_info_obj
, info
.load_address
, info
.load_size
);
270 LOG_INFO("%s: Success loading library %s", __FUNCTION__
, library_name
);
274 // Used for opening the library in a regular file.
275 class FileLibraryOpener
{
278 crazy_library_t
** library
,
279 const char* library_name
,
280 crazy_context_t
* context
) const;
283 bool FileLibraryOpener::Open(
284 crazy_library_t
** library
,
285 const char* library_name
,
286 crazy_context_t
* context
) const {
287 if (!crazy_library_open(library
, library_name
, context
)) {
288 LOG_ERROR("%s: Could not open %s: %s",
291 crazy_context_get_error(context
));
297 // Used for opening the library in a zip file.
298 class ZipLibraryOpener
{
300 ZipLibraryOpener(const char* zip_file
) : zip_file_(zip_file
) {}
302 crazy_library_t
** library
,
303 const char* library_name
,
304 crazy_context_t
* context
) const;
306 const char* zip_file_
;
309 bool ZipLibraryOpener::Open(
310 crazy_library_t
** library
,
311 const char* library_name
,
312 crazy_context_t
* context
) const {
313 if (!crazy_library_open_in_zip_file(
314 library
, zip_file_
, library_name
, context
)) {
315 LOG_ERROR("%s: Could not open %s in zip file %s: %s",
316 __FUNCTION__
, library_name
, zip_file_
,
317 crazy_context_get_error(context
));
323 } // unnamed namespace
325 // Load a library with the chromium linker. This will also call its
326 // JNI_OnLoad() method, which shall register its methods. Note that
327 // lazy native method resolution will _not_ work after this, because
328 // Dalvik uses the system's dlsym() which won't see the new library,
329 // so explicit registration is mandatory.
330 // |env| is the current JNI environment handle.
331 // |clazz| is the static class handle for org.chromium.base.Linker,
332 // and is ignored here.
333 // |library_name| is the library name (e.g. libfoo.so).
334 // |load_address| is an explicit load address.
335 // |library_info| is a LibInfo handle used to communicate information
336 // with the Java side.
337 // Return true on success.
338 jboolean
LoadLibrary(JNIEnv
* env
,
340 jstring library_name
,
342 jobject lib_info_obj
) {
343 String
lib_name(env
, library_name
);
344 FileLibraryOpener opener
;
345 return GenericLoadLibrary(
346 env
, lib_name
.c_str(),
347 static_cast<size_t>(load_address
), lib_info_obj
, opener
);
350 // Load a library from a zipfile with the chromium linker. The
351 // library in the zipfile must be uncompressed and page aligned.
352 // The basename of the library is given. The library is expected
353 // to be lib/<abi_tag>/crazy.<basename>. The <abi_tag> used will be the
354 // same as the abi for this linker. The "crazy." prefix is included
355 // so that the Android Package Manager doesn't extract the library into
358 // Loading the library will also call its JNI_OnLoad() method, which
359 // shall register its methods. Note that lazy native method resolution
360 // will _not_ work after this, because Dalvik uses the system's dlsym()
361 // which won't see the new library, so explicit registration is mandatory.
363 // |env| is the current JNI environment handle.
364 // |clazz| is the static class handle for org.chromium.base.Linker,
365 // and is ignored here.
366 // |zipfile_name| is the filename of the zipfile containing the library.
367 // |library_name| is the library base name (e.g. libfoo.so).
368 // |load_address| is an explicit load address.
369 // |library_info| is a LibInfo handle used to communicate information
370 // with the Java side.
371 // Returns true on success.
372 jboolean
LoadLibraryInZipFile(JNIEnv
* env
,
374 jstring zipfile_name
,
375 jstring library_name
,
377 jobject lib_info_obj
) {
378 String
zipfile_name_str(env
, zipfile_name
);
379 String
lib_name(env
, library_name
);
380 ZipLibraryOpener
opener(zipfile_name_str
.c_str());
381 return GenericLoadLibrary(
382 env
, lib_name
.c_str(),
383 static_cast<size_t>(load_address
), lib_info_obj
, opener
);
386 // Class holding the Java class and method ID for the Java side Linker
387 // postCallbackOnMainThread method.
388 struct JavaCallbackBindings_class
{
392 // Initialize an instance.
393 bool Init(JNIEnv
* env
, jclass linker_class
) {
394 clazz
= reinterpret_cast<jclass
>(env
->NewGlobalRef(linker_class
));
395 return InitStaticMethodId(env
,
397 "postCallbackOnMainThread",
403 static JavaCallbackBindings_class s_java_callback_bindings
;
405 // Designated receiver function for callbacks from Java. Its name is known
407 // |env| is the current JNI environment handle and is ignored here.
408 // |clazz| is the static class handle for org.chromium.base.Linker,
409 // and is ignored here.
410 // |arg| is a pointer to an allocated crazy_callback_t, deleted after use.
411 void RunCallbackOnUiThread(JNIEnv
* env
, jclass clazz
, jlong arg
) {
412 crazy_callback_t
* callback
= reinterpret_cast<crazy_callback_t
*>(arg
);
414 LOG_INFO("%s: Called back from java with handler %p, opaque %p",
415 __FUNCTION__
, callback
->handler
, callback
->opaque
);
417 crazy_callback_run(callback
);
421 // Request a callback from Java. The supplied crazy_callback_t is valid only
422 // for the duration of this call, so we copy it to a newly allocated
423 // crazy_callback_t and then call the Java side's postCallbackOnMainThread.
424 // This will call back to to our RunCallbackOnUiThread some time
425 // later on the UI thread.
426 // |callback_request| is a crazy_callback_t.
427 // |poster_opaque| is unused.
428 // Returns true if the callback request succeeds.
429 static bool PostForLaterExecution(crazy_callback_t
* callback_request
,
430 void* poster_opaque UNUSED
) {
431 crazy_context_t
* context
= GetCrazyContext();
434 int minimum_jni_version
;
435 crazy_context_get_java_vm(context
,
436 reinterpret_cast<void**>(&vm
),
437 &minimum_jni_version
);
439 // Do not reuse JNIEnv from JNI_OnLoad, but retrieve our own.
441 if (JNI_OK
!= vm
->GetEnv(
442 reinterpret_cast<void**>(&env
), minimum_jni_version
)) {
443 LOG_ERROR("Could not create JNIEnv");
447 // Copy the callback; the one passed as an argument may be temporary.
448 crazy_callback_t
* callback
= new crazy_callback_t();
449 *callback
= *callback_request
;
451 LOG_INFO("%s: Calling back to java with handler %p, opaque %p",
452 __FUNCTION__
, callback
->handler
, callback
->opaque
);
454 jlong arg
= static_cast<jlong
>(reinterpret_cast<intptr_t>(callback
));
455 env
->CallStaticVoidMethod(
456 s_java_callback_bindings
.clazz
, s_java_callback_bindings
.method_id
, arg
);
458 // Back out and return false if we encounter a JNI exception.
459 if (env
->ExceptionCheck() == JNI_TRUE
) {
460 env
->ExceptionDescribe();
461 env
->ExceptionClear();
469 jboolean
CreateSharedRelro(JNIEnv
* env
,
471 jstring library_name
,
473 jobject lib_info_obj
) {
474 String
lib_name(env
, library_name
);
476 LOG_INFO("%s: Called for %s", __FUNCTION__
, lib_name
.c_str());
478 if (!IsValidAddress(load_address
)) {
479 LOG_ERROR("%s: Invalid address 0x%llx", __FUNCTION__
, load_address
);
483 ScopedLibrary library
;
484 if (!crazy_library_find_by_name(lib_name
.c_str(), library
.GetPtr())) {
485 LOG_ERROR("%s: Could not find %s", __FUNCTION__
, lib_name
.c_str());
489 crazy_context_t
* context
= GetCrazyContext();
490 size_t relro_start
= 0;
491 size_t relro_size
= 0;
494 if (!crazy_library_create_shared_relro(library
.Get(),
496 static_cast<size_t>(load_address
),
500 LOG_ERROR("%s: Could not create shared RELRO sharing for %s: %s\n",
503 crazy_context_get_error(context
));
507 s_lib_info_fields
.SetRelroInfo(
508 env
, lib_info_obj
, relro_start
, relro_size
, relro_fd
);
512 jboolean
UseSharedRelro(JNIEnv
* env
,
514 jstring library_name
,
515 jobject lib_info_obj
) {
516 String
lib_name(env
, library_name
);
518 LOG_INFO("%s: called for %s, lib_info_ref=%p",
523 ScopedLibrary library
;
524 if (!crazy_library_find_by_name(lib_name
.c_str(), library
.GetPtr())) {
525 LOG_ERROR("%s: Could not find %s", __FUNCTION__
, lib_name
.c_str());
529 crazy_context_t
* context
= GetCrazyContext();
530 size_t relro_start
= 0;
531 size_t relro_size
= 0;
533 s_lib_info_fields
.GetRelroInfo(
534 env
, lib_info_obj
, &relro_start
, &relro_size
, &relro_fd
);
536 LOG_INFO("%s: library=%s relro start=%p size=%p fd=%d",
543 if (!crazy_library_use_shared_relro(
544 library
.Get(), context
, relro_start
, relro_size
, relro_fd
)) {
545 LOG_ERROR("%s: Could not use shared RELRO for %s: %s",
548 crazy_context_get_error(context
));
552 LOG_INFO("%s: Library %s using shared RELRO section!",
559 jboolean
CanUseSharedRelro(JNIEnv
* env
, jclass clazz
) {
560 return crazy_system_can_share_relro();
563 jlong
GetPageSize(JNIEnv
* env
, jclass clazz
) {
564 jlong result
= static_cast<jlong
>(sysconf(_SC_PAGESIZE
));
565 LOG_INFO("%s: System page size is %lld bytes\n", __FUNCTION__
, result
);
569 const JNINativeMethod kNativeMethods
[] = {
570 {"nativeLoadLibrary",
574 "Lorg/chromium/base/library_loader/Linker$LibInfo;"
577 reinterpret_cast<void*>(&LoadLibrary
)},
578 {"nativeLoadLibraryInZipFile",
583 "Lorg/chromium/base/library_loader/Linker$LibInfo;"
586 reinterpret_cast<void*>(&LoadLibraryInZipFile
)},
587 {"nativeRunCallbackOnUiThread",
592 reinterpret_cast<void*>(&RunCallbackOnUiThread
)},
593 {"nativeCreateSharedRelro",
597 "Lorg/chromium/base/library_loader/Linker$LibInfo;"
600 reinterpret_cast<void*>(&CreateSharedRelro
)},
601 {"nativeUseSharedRelro",
604 "Lorg/chromium/base/library_loader/Linker$LibInfo;"
607 reinterpret_cast<void*>(&UseSharedRelro
)},
608 {"nativeCanUseSharedRelro",
612 reinterpret_cast<void*>(&CanUseSharedRelro
)},
613 {"nativeGetPageSize",
617 reinterpret_cast<void*>(&GetPageSize
)}, };
621 // JNI_OnLoad() hook called when the linker library is loaded through
622 // the regular System.LoadLibrary) API. This shall save the Java VM
623 // handle and initialize LibInfo fields.
624 jint
JNI_OnLoad(JavaVM
* vm
, void* reserved
) {
625 LOG_INFO("%s: Entering", __FUNCTION__
);
628 if (JNI_OK
!= vm
->GetEnv(reinterpret_cast<void**>(&env
), JNI_VERSION_1_4
)) {
629 LOG_ERROR("Could not create JNIEnv");
633 // Register native methods.
635 if (!InitClassReference(env
,
636 "org/chromium/base/library_loader/Linker",
640 LOG_INFO("%s: Registering native methods", __FUNCTION__
);
641 env
->RegisterNatives(linker_class
,
643 sizeof(kNativeMethods
) / sizeof(kNativeMethods
[0]));
645 // Find LibInfo field ids.
646 LOG_INFO("%s: Caching field IDs", __FUNCTION__
);
647 if (!s_lib_info_fields
.Init(env
)) {
651 // Resolve and save the Java side Linker callback class and method.
652 LOG_INFO("%s: Resolving callback bindings", __FUNCTION__
);
653 if (!s_java_callback_bindings
.Init(env
, linker_class
)) {
657 // Save JavaVM* handle into context.
658 crazy_context_t
* context
= GetCrazyContext();
659 crazy_context_set_java_vm(context
, vm
, JNI_VERSION_1_4
);
661 // Register the function that the crazy linker can call to post code
662 // for later execution.
663 crazy_context_set_callback_poster(context
, &PostForLaterExecution
, NULL
);
665 LOG_INFO("%s: Done", __FUNCTION__
);
666 return JNI_VERSION_1_4
;