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This article shows you how to use Java to load and parse so in android, the content is concise and easy to understand, it will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

Theoretical basis

The loading of so is a kind of analytical loading, which is different from dex. Dex loads first to optimize and verify to generate odex, and then parses the odex file, while so is more like loading while parsing, and the main parsing in the loading process is the load segment.

The following is mainly the process of parsing loading from the source code with the so load of the java layer.

Analysis of so loading process of java layer System.loadLibrary entry point

In the java layer, we know that loading the so file is realized through the System.loadLibrary function, so let's take it as an entry point to analyze its call relationship and implementation.

System.loadLibrary is in the file of the function definition system source\ libcore\ luni\ src\ main\ java\ java\ lang\ system.java.

The following is its function definition implementation.

/ / the parameter is the name of the so file to be loaded public static void loadLibrary (String libName) {/ / the function has two parameters by calling the loadLibrary function under Runtime. Parameter 1 is the name of the loaded so file, and parameter 2 is a class loader. Runtime.getRuntime () .loadLibrary (libName, VMStack.getCallingClassLoader ()); loadLibray parsing of} Runtime

Through the loadLibrary function of System.java above, we need to continue to analyze the definition implementation of the loadLibray function in the Runtime.java file.

The position of Runtime's loadLibrary function in android system is

Source\ libcore\ luni\ src\ main\ java\ java\ lang\ Runtime.java file.

The following is the source code for the definition and implementation of the loadLibrary function of Runtime.

/ * Searches for and loads the given shared library using the given ClassLoader. * / void loadLibrary (String libraryName, ClassLoader loader) {if (loader! = null) {/ / find the so file name to load String filename = loader.findLibrary (libraryName) through the loader / / failed to find if (filename = = null) {/ / It's not necessarily true that the ClassLoader used / / System.mapLibraryName, but the default setup does, and it's / / misleading to say we didn't find "libMyLibrary.so" when we / / actually searched for "liblibMyLibrary.so.so". Throw new UnsatisfiedLinkError (loader + "couldn't find\"+ System.mapLibraryName (libraryName) +"\ ");} / / load so file name String error = doLoad (filename, loader); if (error! = null) {throw new UnsatisfiedLinkError (error) } return;} String filename = System.mapLibraryName (libraryName); List candidates = new ArrayList (); String lastError = null; / / Loop through the file path for (String directory: mLibPaths) {/ / file path and file name to concatenate String candidate = directory + filename; candidates.add (candidate) If (IoUtils.canOpenReadOnly (candidate)) {String error = doLoad (candidate, loader); if (error = = null) {return; / / We successfully loaded the library. Job done. } lastError = error;}} if (lastError! = null) {throw new UnsatisfiedLinkError (lastError);} throw new UnsatisfiedLinkError ("Library" + libraryName + "not found; tried" + candidates); doLoad parsing of} Runtime

Through the loadLibrary function of Runtime above, we can see that the function that loads so goes to the doLoad function, so we need to continue to analyze the definition and implementation of the doload function under Runtime.

The doload function under Rutime in the system

Source\ libcore\ luni\ src\ main\ java\ java\ lang\ Runtime.java file.

The following code is a defined implementation of the doload function for Runtime.

Private String doLoad (String name, ClassLoader loader) {/ / Android apps are forked from the zygote, so they can't have a custom LD_LIBRARY_PATH, / / which means that by default an app's shared library directory isn't on LD_LIBRARY_PATH. / / The PathClassLoader set up by frameworks/base knows the appropriate path, so we can load / / libraries with no dependencies just fine, but an app that has multiple libraries that / / depend on each other needed to load them in most-dependent-first order. / / We added API to Android's dynamic linker so we can update the library path used for / / the currently-running process. We pull the desired path out of the ClassLoader here / / and pass it to nativeLoad so that it can call the private dynamic linker API. / / We didn't just change frameworks/base to update the LD_LIBRARY_PATH once at the / / beginning because multiple apks can run in the same process and third party code can / / use its own BaseDexClassLoader. / / We didn't just add a dlopen_with_custom_LD_LIBRARY_PATH call because we wanted any / / dlopen (3) calls made from a. So's JNI_OnLoad to work too / / So, find out what the native library search path is for the ClassLoader in question... String ldLibraryPath = null; if (loader! = null & & loader instanceof BaseDexClassLoader) {ldLibraryPath = ((BaseDexClassLoader) loader) .getLdLibraryPath ();} / nativeLoad should be synchronized so there's only one LD_LIBRARY_PATH in use regardless / / of how many ClassLoaders are in the system, but dalvik doesn't support synchronized / / internal natives. Synchronized (this) {return nativeLoad (name, loader, ldLibraryPath);}}

From the above analysis of the source code implementation process, we can see that the interface for Android to load so in the java layer is System.loadLibrary (), and the loading so of the java layer is realized through the layer-by-layer progressive relationship.

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