For those days, you will want the Fishbrain app, with its new BiteTime feature, which helps keen anglers plan ahead and know where and when is the best time to catch a certain fish. However, there will be other times where you don’t want to sit there like a chump, in the vague hope a prize trout or bass gets hooked. So, for each pointer _nl_symbol_ptr and _la_symbol_ptr, we are able to find the corresponding symbol and then the corresponding string to compare against the requested symbol names, and if there is a match, we replace the pointer in the section with the replacement.Fishing may sometimes be about relaxing by the river bank with your line in the water, and waiting to see what bites. The symbol table itself is an array of struct nlists (see ), and each nlist contains an index into the string table in _LINKEDIT which where the actual symbol names are stored. So, given struct section nl_symbol_ptr, the corresponding index in the symbol table of the first address in that section is indirect_symbol_table. The indirect symbol table, which is located in the _LINKEDIT segment of the binary, is just an array of indexes into the symbol table (also in _LINKEDIT) whose order is identical to that of the pointers in the non-lazy and lazy symbol sections. For the two relevant sections, the section headers ( struct sections from ) provide an offset (in the reserved1 field) into what is known as the indirect symbol table. In order to find the name of the symbol that corresponds to a particular location in one of these sections, we have to jump through several layers of indirection. _nl_symbol_ptr is an array of pointers to non-lazily bound data (these are bound at the time a library is loaded) and _la_symbol_ptr is an array of pointers to imported functions that is generally filled by a routine called dyld_stub_binder during the first call to that symbol (it's also possible to tell dyld to bind these at launch). fishhook re-binds these symbols by determining the locations to update for each of the symbol names passed to rebind_symbols and then writing out the corresponding replacements.įor a given image, the _DATA segment may contain two sections that are relevant for dynamic symbol bindings: _nl_symbol_ptr and _la_symbol_ptr. Return UIApplicationMain(argc, argv, nil, NSStringFromClass()) Ĭalling real open('/var/mobile/Applications/161DA598-5B83-41F5-8A44-675491AF6A2C/Test.app/Test', 0)ĭyld binds lazy and non-lazy symbols by updating pointers in particular sections of the _DATA segment of a Mach-O binary. Printf( "Mach-O Magic Number: %x \n ", magic_number) Open our own binary and print out first 4 bytes (which is the same // for all Mach-O binaries on a given architecture) int fd = open(argv, O_RDONLY) Int my_open( const char *path, int oflag. Printf( "Calling real close( %d) \n ", fd) Static int (*orig_open)( const char *, int. # import "fishhook.h " static int (*orig_close)( int)
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