The reserved value is only present in 64-bit Mach-O files. The magic number for 64-bit architectures is 0xfeedfacf, so the first 4 bytes of the header will be 0xfe 0xed 0xfa 0xcf, in that order, if the code is for a big-endian architecture and 0xcf 0xfa 0xed 0xfe, in that order, if the code is for a little-endian architecture. The magic number for 32-bit code is 0xfeedface, so the first 4 bytes of the header will be 0xfe 0xed 0xfa 0xce, in that order, if the code is for a big-endian instruction set architecture such as PowerPC on a Mac, and will be 0xce 0xfa 0xed 0xfe, in that order, if the code is for a little-endian instruction set architecture such as x86 or ARM. Īll multi-byte values in all data structures are written in the byte order of the host for which the code was produced. The Accent file format was in turn, based on an idea from Spice Lisp. The basic structure-a list of variable-length "load commands" that reference pages of data elsewhere in the file -was also used in the executable file format for Accent. When looking up symbols Mach-O uses a two-level namespace that encodes each symbol into an 'object/symbol name' pair that is then linearly searched for, first by the object and then the symbol name. Mach-O uses the REL relocation format to handle references to symbols. NeXTSTEP, macOS, and iOS are examples of systems that use this format for native executables, libraries and object code.Įach Mach-O file is made up of one Mach-O header, followed by a series of load commands, followed by one or more segments, each of which contains between 0 and 255 sections. Mach-O is used by some systems based on the Mach kernel. It was developed to replace the a.out format. Mach-O, short for Mach object file format, is a file format for executables, object code, shared libraries, dynamically loaded code, and core dumps. Binary, executable, object, shared libraries, core dumpĪRM, SPARC, PA-RISC, PowerPC and x86 executable code, memory image dumps
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