Keith Smiley keith

macOS Internals

Understand your Mac and iPhone more deeply by tracing the evolution of Mac OS X from prelease to Swift. John Siracusa delivers the details.

Starting Points

How to use this gist

You've got two main options:

theme

class

highlighter

fonts

default

text-center

MaskRay

sans	serif	mono
sans-serif	serif	monospace

ELF Format Cheatsheet

Introduction

Executable and Linkable Format (ELF), is the default binary format on Linux-based systems.

Compilation

Debugging the Swift Toolchain

Use these steps to debug components of the Swift toolchain. This allows you to see Swift's source code from the debugger – instead of disassembly. The debugger can also provide some variable names and values. This has been initially tested with libswiftCore.dylib.

These instructions were updated as of Swift 5.2.1.

Prerequisites

iOS app introspection

Jailbreak in 2025
Create Provisioning Profile in XCode

libdispatch efficiency tips

The libdispatch is one of the most misused API due to the way it was presented to us when it was introduced and for many years after that, and due to the confusing documentation and API. This page is a compilation of important things to know if you're going to use this library. Many references are available at the end of this document pointing to comments from Apple's very own libdispatch maintainer (Pierre Habouzit).

My take-aways are:

You should create very few, long-lived, well-defined queues. These queues should be seen as execution contexts in your program (gui, background work, ...) that benefit from executing in parallel. An important thing to note is that if these queues are all active at once, you will get as many threads running. In most apps, you probably do not need to create more than 3 or 4 queues.
Go serial first, and as you find performance bottle necks, measure why, and if concurrency helps, apply with care, always validating under system pressure. Reuse

Forward GnuPG agent from macOS to Linux

On the remote machine

Run gpg once as your to create the directory structure

gpg --list-keys

	from os import urandom
	from socket import create_connection

	from cryptography.hazmat.primitives.asymmetric import padding
	from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
	from cryptography.hazmat.primitives.serialization import load_der_public_key


	def read(sock, length):
	result = b''

	// Example usage:
	// Swizzler<NSString , NSDateFormatter , NSDate *> NSDateFormatter_stringFromDate_ {
	// NSDateFormatter.class, @selector(stringFromDate:), [&](auto self, auto date) {
	// if ([NSCalendar.currentCalendar components:NSCalendarUnitWeekday fromDate:date].weekday == 4) {
	// return @"It Is Wednesday My Dudes";
	// } else {
	// return NSDateFormatter_stringFromDate_(self, date);
	// }
	// }
	// };

	wget --no-check-certificate --recursive --domains=opensource.apple.com --no-clobber --accept "*.gz" --no-parent -l2 https://opensource.apple.com/tarballs
	wget --no-check-certificate --recursive --domains=opensource.apple.com --no-clobber --accept "*.gz" -l2 https://opensource.apple.com/
	wget --no-check-certificate --recursive --domains=opensource.apple.com --no-clobber --accept "*.gz" --no-parent -l3 https://opensource.apple.com/darwinbuild/