TuT [Tutorial] Logos + Objective-C

[castix 18.4k iPhone X 12.1.1]

 
 
 
Logos - Definition
The syntax provided by Logos greatly simplifies the development of MobileSubstrate extensions ("tweaks") which can hook other methods throughout the OS. In this context, "method hooking" refers to a technique used to replace or modify methods of classes found in other applications on the phone. They can also be used for replacing original values which is called cheating. That's what we do.
 
 
 
Logos - Directives
 
Block-Principle
Logos are written in code blocks. They must be closed by %end. You can't have a block within a second one. Each block has to be assigned with a unique name in order to work.
 
 
 
%group

%group Groupname

Begin a hook group with the name Groupname. All ungrouped hooks are in the implicit "_ungrouped" group by default. %group is very useful to organize your code and structure it.
 
 
 
 
%hook

%hook Classname

Open a hook block for the class named Classname.
Can be inside a %group block.
Here is an example:

%hook SpringBoard
- (BOOL)homeScreenRotationStyleWantsUIKitRotation {
     return true;
}
-(BOOL)homeScreenSupportsRotation {
     return true;
}
%end

%hook SBIconLabelImageParameters {
     (id)text {
     %orig; //This calls the original implementation of a method
     return;
}
%end

PS: There is a Tweak for custom enabling screen rotation for all iDevices inside
 
 
 
 
%subclass

%subclass Classname: Superclass <Protocol, Protocol>

Subclass block - the class is created at runtime and populated with methods. ivars are not yet supported (use associated objects). The %new specifier is needed for a method that doesn't exist in the superclass. To instantiate an object of the new class, you can use the %c operator.
Can be inside a %group block.
 
 
 
%new

%new
%new(signature)

Add a new method to a hooked class or subclass. signature is the Objective-C type encoding for the new method. If it is omitted, one will be automatically generated. %new generates a new instance subclass independent from a block. more than one subclasses can persist at a time.
Can be inside a %group block.
 
 
 
 
%end

%end

Close a group/hook/subclass block.
 
 
 
Top Level
The directives in this category should not exist within a group/hook/subclass block.
 
 

 

%config

%config(X=Y);

Set a logos configuration flag.
Configuration Flags

• generator
  • MobileSubstrate generate code that uses MobileSubstrate for hooking. internal generate code that uses only internal Objective-C runtime methods for hooking.
• warnings
  • none suppress all warnings default non-fatal warnings error make all warnings fatal
• dump
  • yaml dump the internal parse tree in YAML format

 

 

%ctor

%ctor { … }

Generate an anonymous constructor (of default priority). You may already know that "__attribute__((constructor)) void DylibMain(){...}"
 
 
 
 
Function level
The directives in this category should only exist within a function block.
 

 
%init

%init;
%init([<class>=<expr>, …]);
%init(Group[, [+|-]<class>=<expr>, …]);

Initialize a group (or the default group). Passing no group name will initialize "_ungrouped", and passing class=expr arguments will substitute the given expressions for those classes at initialization time. The + sigil (as in class methods in Objective-C) can be prepended to the classname to substitute an expression for the metaclass. If not specified, the sigil defaults to -, to substitute the class itself. If not specified, the metaclass is derived from the class.
 
 
 
 
 
%class

%class Class;

%class is deprecated. Do not use it in new code.
Forward-declare a class. Outmoded by %c, but still exists. Creates a $Class variable, and initializes it with the "_ungrouped" group. %class initialzizes a new class. (Also fixes mismatch with %hook Level)
 
 
 
 
%c

%c([+|-]Class)

Evaluates to Class at runtime. If the + sigil is specified, it evaluates to MetaClass instead of Class. If not specified, the sigil defaults to -, evaluating to Class.
 
 
 
 
%orig

%orig
%orig(arg1, …)

Call the original hooked method. Doesn't function in a %new'd method. Works in subclasses, strangely enough, because
MobileSubstrate will generate a supercall closure at hook time.
(If the hooked method doesn't exist in the class we're hooking, it creates a stub that just calls the superclass implementation.) args
is passed to the original function - don't include self and _cmd, Logos does this for you.

 
 
  %log

%log;
%log([(<type>)<expr>, …]);

Dump the method arguments to syslog. Typed arguments included in %log will be logged as well.

 
 
  File Extensions for Logos
Extension Process order .x will be processed by Logos, then preprocessed and compiled as objective-c. .xm will be processed by Logos, then preprocessed and compiled as objective-c++. .xi will be preprocessed as objective-c first, then Logos will process the result, and then it will be compiled. .xmi will be preprocessed as objective-c++ first, then Logos will process the result, and then it will be compiled. xi or xmi files can use Logos directives in #define macros.
 
 
 
 
  Splitting Logos Hooking Code Across Multiple Files
By default, the Logos pre-processor will only process one .xm file at build time. However, it is possible to split the Logos hooking code into multiple files.
First, the main file has to be renamed to an .xmi file. Then, other .xm files can be included in it using the #include directive. The Logos pre-processor will add those files to the main file before processing it.
 
 
Special thanks to KennyTM͠   for his explanations and contributions to iphonedevwiki

[mehdiphone 7.3k 8 8.1.2]

Very good, very clean, good tutorial castix

[Rook 536k iPad Pro (2nd gen) 17.4 Donor]

Is this all from iPhoneDevWiki or did you add some modifications yourself?

[castix 18.4k iPhone X 12.1.1]

Is this all from iPhoneDevWiki or did you add some modifications yourself?

 

I added explanations and additional info to some Logos as well. Mainly to those which are often used by users here (Refer to %hook, %new, %ctor). I also simplified things

[AnotherLurker 1.5k]

%hook SBIconLabelImageParameters {
     return %orig; //This calls the original implementation of a method
     return;
}
%end

This is wrong on so many levels....

 

but other that, good job!

[castix 18.4k iPhone X 12.1.1]

I know is didn't have time to check everything

[KingRalph 808 9.3.5]

You should add a section in this thread for the "essential"/"common" terms

The only thing that most ms hackers need to know are:

%hook

%ctor

%new

%orig

%end

 

It'll be easier for people to find the explanation for the commonly used terms

[i0s_tweak3r 12.3k iPhone X 13.5]

Awesome tutorial.  Very well explained. ??