Objective-CS and the llvm-objcs Toolchin

Dragon ships with builtin integration for the llvm-objcs toolchain and the Objective-CS hooking language.

It provides wrappers, utilities, and commands that help set up the toolchain and get autocomplete, editor support, etc working with clangd.

A companion extension for vscode exists at [LINKHERE]

Adding support to a project should be fairly drop-in. Projects using Objective-CS can still use logos, they will just need to be in separate files for autocomplete, etc to work.

Objective-CS

Objective-CS is an extension of Objective-C designed to provide easier integration with hooking APIs than working in purely Objective-C.

By building our language directly within llvm as opposed to via a preprocessor (logos), we gain access to a large amount of existing tooling that already supports LLVM.

This allows autocomplete, inline error messages/help/suggestions, and the myriad other clangd features to work within Objective-CS files.

File Extension

Currently, Objective-CS just adds support directly into Objective-C code, so you use the same .m or .mm extension as regular objc. Eventually it may be gated or aliased to .mx/.mmx.

Basic Syntax

The following code block demos the full current featureset of Objective-CS

// Predeclaring the interface for what we're hoooking isn't required,
// but it allows us to:
//    autocomplete hook selectors
//    access ivars of the class we're hooking
//    declare new methods we want to add
@interface SBIconView : UIView
{
    BOOL _allowsLabelArea; // Declare ivars we want to "hook" (access) here
    CGFloat _iconImageAlpha; // This replaces the need for swapping to ObjC++ and wrangling the MSHookIvar API.
}

-(void)configureForLabelAllowed:(BOOL)allowed;

@new
-(void)myAwesomeNewInstanceMethod;

@end

// If you've already imported a header for a given class (from a patched SDK that has proper headers),
// you can instead declare a category ( `@interface SBIconView ()` ) and still utilize these features.
// This accomplishes the same thing in terms of
//    applying new methods, accessing ivars that maybe didn't exist in the header you imported, etc.

// --

@group iOS13Plus
@hook SBIconView

-(void)myAwesomeNewInstanceMethod
{
  NSLog(@"Hello from Objective-CS!");
}

-(void)configureForLabelAllowed:(BOOL)allowed
{
    @orig(NO);
    _allowsLabelArea = NO;
    _iconImageAlpha = 0.5;
    [self myAwesomeNewInstanceMethod];
}

@end
@end

#ifndef kCFCoreFoundationVersionNumber_iOS_13_0
#define kCFCoreFoundationVersionNumber_iOS_13_0 1665.15
#endif

// This is a manually declared constructor. This is not required if you are not using groups.
// You *will* need to use one if you are using groups, as all groups must be initialized for their hooks to be applied.
// _eventually,_ something like @ctor (analogous to logos' %ctor) may be added.
__attribute__((constructor))
void initFunc(void)
{
  if (kCFCoreFoundationVersionNumber >= kCFCoreFoundationVersionNumber_iOS_13_0){
    @init(iOS13Plus);
    // initialize multiple groups: @init(myGroup, mySecondGroup, andSoOn);
  }
}

Future

Plans exist to add support for: * @hookf(FunctionName) * @ctor{} * @subclass

This is a hobby project with one developer, so there is no timeframe on these plans :)

llvm-objcs

LLVM-objcs is a fork of Apple’s LLVM that supports compiling Objective-CS code.

It aims to support the same featureset as apple-llvm, however modules have been an undocumented pain to compile support for, so the currently distributed binaries do not yet support them (i.e. @import UIKit;. Just import headers normally for now).

Builds are available in arm64 and x86_64 form for macOS, <upcoming> linux, and iOS (iOS is arm64 only, silly)</upcoming>

Installing

dragon lo setup will download and install the appropriate toolchain for your system.

It will also be automatically installed if a DragonMake project declares it as required, and it isn’t already installed.

Manually

Download or build the appropriate toolchain and extract/install it in ~/.dragon/llvm-objcs. The directory structure should be as follows:

serket@prospit ~ % tree ~/.dragon/llvm-objcs -L 1
/Users/serket/.dragon/llvm-objcs
├── bin
├── include
├── lib
├── libexec
└── share

After that you’re good to go.

Future

As this toolchain was built off of llvm-17, it does not support arm64e libraries injected into arm64e processes for pre-iOS 14 devices.

This is an issue with all toolchains post llvm-12, and workarounds are being looked into.