1 files changed, 207 insertions, 0 deletions
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