12/11/2023 0 Comments Cmi advance dcommandsIt’s these sections that can be of profound interest to developers and reverse engineerers since they each serve a unique purpose to the program. Finally, Segment Command 3 doesn’t point to any offset in the executable. Segment Command 1, points to an offset in the executable that contains four section commands, while Segment Command 2 points to an offset that contains 0 section commands. These are more finely-grained areas bound by the same memory protections given by their parent segment. Segments can have 0 or more subcomponents called sections. This means that executable code and the address to global variables will live in separate segments. Other parts of the program, such as global variables or singletons, need read and write permissions, but not executable permissions. For example, executable code should only have read and execute permissions it doesn’t need write permissions. Think of segments as areas of memory that have a specific type of memory protection. Some of the load commands provide instructions about how to load segments. Load commands are instructions on how to load the program and are made up of C structs, which vary in size depending on the type of load command. This is the layout of every compiled executable every main program, every framework, every kernel extension, everything that’s compiled on an Apple platform.Īt the start of every compiled Apple program is the Mach-O header that gives information about the CPU this program can run on, the type of executable it is (A framework? A standalone program?) as well as how many load commands immediately follow it. Terminologyīefore diving into the weeds with all the different C structs you’re about to view, it would be best to take a high level view of the Mach-O layout. Make sure you have that caffeine on board for this chapter since the theory comes first, followed by the fun in the following chapter. This chapter introduces the concepts of Mach-O, while the next chapter, Mach-O Fun will show the amusing things that are possible with this knowledge.
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