![]() So add some regular expression logic to a script to parse out those without the string passed in. While symbols and Mach-O may seem very specific it’s just basic string matching. For example, the first symbol for zprint is _CFDictionaryApplyFunction so we’d run a script to search for _CFDictionaryApplyFunction – it would take a long time to run but would eventually output a list of binaries that call the _CFDictionaryApplyFunction symbol. Once we have a list of symbols, we could extend our use a bit further to find all files that use certain symbols by recursively checking all directories from a given working directory to list all files with a given string in the symbol list. So nm /somedocument throws an error whereas nm /usr/bin/zprint (as an example) outputs a list of symbols. Notice that after the path to a file name passed and then a :, that Mach-O is the first string that appears.Ī reason we’re just checking that it’s Mach-O after the path to the file is that different Mach-O types have different outputs, but they can all work with nm. Applications/Little Snitch.app/Contents/MacOS/Little Snitch (for architecture arm64): Mach-O 64-bit executable arm64 Applications/Little Snitch.app/Contents/MacOS/Little Snitch (for architecture x86_64): Mach-O 64-bit executable x86_64 Applications/Little Snitch.app/Contents/MacOS/Little Snitch: Mach-O universal binary with 2 architectures: So prior to checking we can use the file command to make sure a file is a Mach-O binary.įile /Applications/Little\ Snitch.app/Contents/MacOS/Little\ Snitch However, nm fails if the file isn’t a mach-O object file. This can be useful to find what behaviors might be supported by a given binary, those that leverage deprecated APIs, etc. Nm /Applications/Little\ Snitch.app/Contents/MacOS/Little\ Snitch We can use the nm command to extract a list of symbols used as follows: Per the man page of nm, “nm displays the name list (symbol table of nlist structures) of each object file in the argument list.,” The basics of compiler programming aside, let’s take a basic task: show all the symbols used in a binary compiled for a Mac (or a mach-O object file). Tools like Hopper Disassembler can be used to look at these files and extract symbols, or a command like nm. We can see those APIs by extracting a list of symbols, but not really the logic underlying it. Many of those symbols are APIs that Apple makes available that the code uses. ![]() ![]() ![]() There’s a Mach-O header and then load commands and segments of up to 255 sections with references to symbols encoded into objects and symbol names. A Mach-O object file is a file format used for executables, libraries, object code, and core dumps. ![]()
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