Requeriments to decompile Stock System for Xperia Devices:
-Have a FTF Firmware for your Xperia Device (JB - KitKat - Lollipop)
-Have a FlashTool
-WinRar or WinZip
-Patience.exe
-Brain.exe
And more tools (on this Repository)
How to decompile Stock System for Xperia Devices:
-Open your FTF File with WinRar or WinZip.
-Extract your System.sin on any directory.
-Open your FlashTool.
-Select Tools -> Sin Editor.
-Select you System.sin in the directory of the Sin Editor.
-Click on "Extract Data".
-Wait a few minutes.
-Open You Ext4_Unpacker.exe.
-Select System.ext4.
-Select All Files on the ext4 File.
-Click right and Extract Files.
-Create a new folder to extract the files.
-Wait a few minutes.
-And Ready :D .