diff options
Diffstat (limited to 'libdmitry')
| -rwxr-xr-x | libdmitry/Android.mk | 26 | ||||
| -rwxr-xr-x | libdmitry/libdmitry.c | 207 |
2 files changed, 233 insertions, 0 deletions
diff --git a/libdmitry/Android.mk b/libdmitry/Android.mk new file mode 100755 index 0000000..5457c8b --- /dev/null +++ b/libdmitry/Android.mk @@ -0,0 +1,26 @@ +# Copyright (C) 2015 The Android Open Source Project
+# Written by Dmitry Grinberg
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+LOCAL_PATH := $(call my-dir)
+
+
+include $(CLEAR_VARS)
+
+LOCAL_SHARED_LIBRARIES := liblog libcutils libgui libbinder libutils
+LOCAL_SRC_FILES := libdmitry.c
+LOCAL_MODULE := libdmitry
+LOCAL_MODULE_TAGS := optional
+include $(BUILD_SHARED_LIBRARY)
\ No newline at end of file diff --git a/libdmitry/libdmitry.c b/libdmitry/libdmitry.c new file mode 100755 index 0000000..6472263 --- /dev/null +++ b/libdmitry/libdmitry.c @@ -0,0 +1,207 @@ +#define LOG_TAG "libdmitry"
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <pthread.h>
+#include <utils/Log.h>
+#include <hardware/power.h>
+#include <hardware/hardware.h>
+
+/*
+ * CURIOUS WHAT THE HELL IS GOING ON IN HERE? READ UP...
+ *
+ *
+ * Problems:
+ * 1. Nexus 10's GPS library was made to work with android L
+ * 2. Android M changed a few things around that make it not work
+ * a. Sensor manager API changed in a few places
+ * b. BoringSSL replaced OpenSSL
+ * 3. Due to these now-missing unresolved symbols GPS library will not load or run
+ *
+ * Curious data snippets
+ * Due to peculiarities of the ELF format, when a binary baz imports function foo() from libbar.so,
+ * nowhere in baz's ELF file does it say that foo() must from from libbar. In fact there are two
+ * separate records. One that says that libbar is "NEED"ed, and another that says that there is an
+ * import of function "foo". What that means is that if the process wer to also load libxyz, which
+ * also exported foo(), there is no way to be sure which foo() would get called. Why do we care?
+ * Well, consider out problems above. We need to provide functions and variables that existing
+ * libraries no longer do. How?
+ *
+ * A tricky but clever solution: INTERPOSITION library
+ * 1. We'll edit the GPS library and replace one of its "NEED" record with one referencing a new library
+ * which we'll create. Need a library name? why not "lidmitry"?
+ * 2. Make sure that lidmitry's NEED records include the library whose record we replaced in the GPS
+ * library, to make sure that the linker brings it in afterall and all symbols in it are found
+ * 3. Implement libdmitry such that it provides the missing things and does them in such a way that the
+ * GPS library is happy.
+ * 4. Complications exist:
+ * a. This would be impossible to do in C++, as the compiler would barf at us implementing random
+ * chunks of random classes we do not control. Luckily, the linker has no idea about C++, C, or other
+ * such things. C++ names get converted to special symbol names by the compiler, and thus the linker
+ * is neevr even aware of overloading or such things. This process is called mangling. So we'll just
+ * export the C++ functions we need with the proper mangled names, and code them in C. This means
+ * that we need to follow the proper calling conventions by hand, etc. With some dissasembling to see
+ * how GCC does it, we can duplicate it here, as I did.
+ * b. Not all missing things are functions. There are a few variables that need to be exported and are
+ * not present in M's code. We have to provide them. Luckily, just like with functions, as long as our
+ * mandled name matches, the linker will be happy to make the connection for us.
+ * c. Some cleanup may be needed on exit. Luckily, there is a way to register functions to be called
+ * upon library load and unload. I use that here to free some state that may be left over on exit.
+ *
+ * Result: GPS library works on M, with the help of libdmitry and a small binary patch to the GPS
+ * library itself (replacing one of the "NEED" records with a NEED record for "libdmitry"
+ */
+
+
+
+
+
+
+
+//various funcs we'll need to call, in their mangled form
+
+ //android::String8::String8(char const*)
+ extern void _ZN7android7String8C1EPKc(void **str8P, const char *str);
+
+ //android::String8::~String8()
+ extern void _ZN7android7String8D1Ev(void **str8P);
+
+ //android::String16::String16(char const*)
+ extern void _ZN7android8String16C1EPKc(void **str16P, const char *str);
+
+ //android::String16::~String16()
+ extern void _ZN7android8String16D1Ev(void **str16P);
+
+ //android::SensorManager::~SensorManager()
+ extern void _ZN7android13SensorManagerD1Ev(void *sensorMgr);
+
+ //android::SensorManager::SensorManager(android::String16 const&)
+ extern void _ZN7android13SensorManagerC1ERKNS_8String16E(void *sensorMgr, void **str16P);
+
+ //android::SensorManager::createEventQueue(android::String8, int)
+ extern void _ZN7android13SensorManager16createEventQueueENS_7String8Ei(void **retVal, void *sensorMgr, void **str8P, int mode);
+
+
+//data exports we must provide for gps library to be happy
+
+ /*
+ * DATA: android::Singleton<android::SensorManager>::sLock
+ * USE: INTERPOSE: a mutes that GPS lib will insist on accessing
+ * NOTES: In L, the sensor manager exposed this lock that callers
+ * actually locked & unlocked when accessing it. In M this
+ * is no longer the case, but we still must provide it for
+ * the GPS library to be happy. It will lock nothnhing, but
+ * as long as it is a real lock and pthread_mutex_* funcs
+ * work on it, the GPS library will be happy.
+ */
+ pthread_mutex_t _ZN7android9SingletonINS_13SensorManagerEE5sLockE = PTHREAD_MUTEX_INITIALIZER;
+
+ /*
+ * DATA: android::Singleton<android::SensorManager>::sInstance
+ * USE: INTERPOSE: a singleton instance of SensorManager
+ * NOTES: In L, the sensor manager exposed this variable, as it was
+ * a singleton and one could just access this directly to get
+ * the current already-existing instance if it happened to
+ * already exist. If not one would create one and store it
+ * there. In M this is entirely different, but the GPS library
+ * does not know that. So we'll init it to NULL to signify that
+ * no current instance exists, let it create one, and store it
+ * here, and upon unloading we'll clean it up, if it is not
+ * NULL (which is what it would be if the GPS library itself
+ * did the cleanup).
+ */
+ void* _ZN7android9SingletonINS_13SensorManagerEE9sInstanceE = NULL;
+
+
+//code exports we provide
+
+ //android::SensorManager::SensorManager(void)
+ void _ZN7android13SensorManagerC1Ev(void *sensorMgr);
+
+ //android::SensorManager::createEventQueue(void)
+ void _ZN7android13SensorManager16createEventQueueEv(void **retVal, void *sensorMgr);
+
+ //this used to exist in OpenSLL, but does not in BoringSSL - for some reason GPS library uses it anyways
+ void *CRYPTO_malloc(uint32_t sz, const char *file, uint32_t line);
+
+
+//library on-load and on-unload handlers (to help us set things up and tear them down)
+ void libEvtLoading(void) __attribute__((constructor));
+ void libEvtUnloading(void) __attribute__((destructor));
+
+
+/*
+ * FUNCTION: android::SensorManager::SensorManager(void)
+ * USE: INTERPOSE: construct a sensor manager object
+ * NOTES: This constructor no longer exists in M, instead now one must pass
+ * in a package name as a "string16" to the consrtuctor. Since this
+ * lib only services GPS library, it is easy for us to just do that
+ * and this provide the constructor that the GPS library wants.
+ * The package name we use if "gps.default". Why not?
+ */
+void _ZN7android13SensorManagerC1Ev(void *sensorMgr)
+{
+ void *string;
+
+ _ZN7android8String16C1EPKc(&string, "gps.default");
+ _ZN7android13SensorManagerC1ERKNS_8String16E(sensorMgr, &string);
+ _ZN7android8String16D1Ev(&string);
+}
+
+/*
+ * FUNCTION: android::SensorManager::createEventQueue(void)
+ * USE: INTERPOSE: create an event queue to receive events
+ * NOTES: This function no longer exists in M, instead now one must pass
+ * in a client name as a "string8" and an integer "mode"to it. M
+ * sources list default values for these params as an empty string
+ * and 0. So we'll craft the same call here.
+ */
+void _ZN7android13SensorManager16createEventQueueEv(void **retVal, void *sensorMgr)
+{
+ void *string;
+
+ _ZN7android7String8C1EPKc(&string, "");
+ _ZN7android13SensorManager16createEventQueueENS_7String8Ei(retVal, sensorMgr, &string, 0);
+ _ZN7android7String8D1Ev(&string);
+}
+
+/*
+ * FUNCTION: CRYPTO_malloc(uint32_t sz, const char *file, uint32_t line)
+ * USE: INTERPOSE: Allocate memory
+ * NOTES: In OpenSSL, this just allocates memory and optionally tracks it.
+ * Why manta's GPS library chose to use it is a mystery, but to make
+ * it happy we must provide it, so we do, backing the allocation with
+ * a calloc()-ed memory chunk.
+ */
+void *CRYPTO_malloc(uint32_t sz, const char *file, uint32_t line)
+{
+ (void)file;
+ (void)line;
+ return calloc(sz, 1);
+}
+
+/*
+ * FUNCTION: libEvtLoading()
+ * USE: Handle library loading
+ * NOTES: This is a good time to log the fact that we were loaded and plan to
+ * do our thing.
+ */
+void libEvtLoading(void)
+{
+ ALOGI("Nexus 10 GPS interposition library loaded. Your GPS should work in M now.");
+}
+
+/*
+ * FUNCTION: libEvtUnloading()
+ * USE: Handle library unloading
+ * NOTES: This is a good time to free whatever is unfreed and say goodbye
+ */
+void libEvtUnloading(void)
+{
+ ALOGI("Nexus 10 GPS interposition library unloading. Goodbye...");
+ if (_ZN7android9SingletonINS_13SensorManagerEE9sInstanceE) {
+ //if an instance stil exists, free it by calling the destructor, just to be throrough
+ _ZN7android13SensorManagerD1Ev(_ZN7android9SingletonINS_13SensorManagerEE9sInstanceE);
+ _ZN7android9SingletonINS_13SensorManagerEE9sInstanceE = NULL;
+ }
+}
\ No newline at end of file |