It can be viewed and managed by the codesign tool that allows to work with different signature parts. While code signature is freely available via open-source, just as in many other open-source projects, it is pretty badly documented. There is also a separate table with necessary data employed by dynamic loader for each external symbol.Ĭode signature. Another dynamic symbol table links each import table entry to the corresponding symbol. Names of symbols from the main symbol table are contained in a separate string table. Each entry represents a certain part of the code via specifying name offset in the string table, ordinal section, type, or any other specific information. Table is divided depending on whether the symbol is local, external, or debug. All currently used symbols, both locally and externally defined, as well as stubs, generated via external calls executed via import table, are contained in the main symbol table. Load command for loading CoreFoundation binary Moreover, load commands also include locations of import and stub tables, symbol tables, as well as table that contains information for dynamic loader. Load commands describe each dynamic library dependency and include paths to corresponding binary files. They start with command type and size, which may vary from one command to another. Segments are divided by sections, each storing a certain type of information.Īll segments are byte streams. Large parts of executable that are mapped to a certain virtual address space by the loader are called segments. Sections and segments of executable, as well as their mapping to virtual memory.Load commands provide the crucial information for loading image: Mach Header of the first executable in 'fat' binaryĮach mach header starts with the 0xfeedface magic number and contains general information about the executable, such as target CPU type, subtype, loading options and load commands count and offset. Mach Header of executable in 'thin' binary The fat header starts with the 0xcafebabe magic number and contains information about every executable that resides in the binary file: CPU type and subtype, file offset and align values. Different types of binaries employ different headers, with thin binaries using mach header and fat binaries using their own fat header, used to describe where all the mach headers in the binary are located. Header always begins with a magic number that serves identification purposes. Thus, header is something that every binary starts with. Header is the first thing that loader reads when loading image. The most important part of iOS or OS X executable is the header. Fat binaries are usually employed to combine executable code in a single file. While thin binary has a sole Mach-O executable, fat binary can have many of them at once. It can be contained in either 'thin' binaries or 'fat' binaries. Mach-O format of executable are very commonly used among the systems based on Mach kernel. Knowing binary structure is paramount in successfully learning how to reverse engineer software.Įxecutable binary format. When reverse engineering a binary, you should now where executable code is situated inside it. In this article we will look at how to reverse engineer iOS app, as well as OS X software, and try to give you some practical advice on what you need to know and what tools you need to have. There are many other cases where you need to reverse engineer software. Making maintenance of legacy code easier.Improving interaction with a particular platform.Improving compatibility with closed solutions and formats.Business situations where reverse engineering will be useful are many and they are very varied: When there is an executable, but no access to the source code, yet you still need to understand the inner workings of this particular software, you apply reverse engineering to it. The question of why we need to employ reverse engineering is an easy one to answer.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |