Difference between revisions of "Logos"

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Logos is a component of the [[Theos]] development suite that allows method hooking code to be written easily and clearly, using a set of special preprocessor directives.
 
Logos is a component of the [[Theos]] development suite that allows method hooking code to be written easily and clearly, using a set of special preprocessor directives.
  
== Overview ==
+
= Overview =
  
 
The syntax provided by Logos greatly simplifies the development of MobileSubstrate extensions ("tweaks") which can hook other methods throughout the OS.
 
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.
 
In this context, "method hooking" refers to a technique used to replace or modify methods of classes found in other applications on the phone.
  
== Getting Logos ==
+
= Getting Logos =
  
 
Logos is distributed with [[Theos]], and you can use Logos' syntax in any Theos-built project without any extra setup.  For more information about Theos, visit [[Theos|its page]].
 
Logos is distributed with [[Theos]], and you can use Logos' syntax in any Theos-built project without any extra setup.  For more information about Theos, visit [[Theos|its page]].
  
== List of Logos Directives ==
+
= List of Logos Directives =
  
=== Block-level ===
+
== Block-level ==
  
The directives in this category open a block of code which must be closed by an %end directive (shown below). These should not exist within functions or methods.
+
The directives in this category open a block of code which must be closed by an <tt>[[Logos#.25end|%end]]</tt> directive (shown below). These should not exist within functions or methods.
  
==== %group ====
+
=== %group ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 48: Line 48:
 
</source>
 
</source>
  
==== %hook ====
+
=== %hook ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 70: Line 70:
 
</source>
 
</source>
  
==== %new ====
+
=== %new ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 81: Line 81:
 
Can be inside a <tt>[[Logos#.25group|%group]]</tt> block.
 
Can be inside a <tt>[[Logos#.25group|%group]]</tt> block.
  
==== %subclass ====
+
=== %subclass ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 123: Line 123:
 
</source>
 
</source>
  
==== %end ====
+
=== %end ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 131: Line 131:
 
Close a group/hook/subclass block.
 
Close a group/hook/subclass block.
  
=== Top level ===
+
== Top level ==
  
 
The directives in this category should not exist within a group/hook/subclass block.
 
The directives in this category should not exist within a group/hook/subclass block.
  
==== %config ====
+
=== %config ===
  
 
<source lang="logos">
 
<source lang="logos">
%config(X=Y);
+
%config(Key=Value);
 
</source>
 
</source>
  
 
Set a logos configuration flag.
 
Set a logos configuration flag.
  
===== Configuration Flags =====
+
==== Configuration Flags ====
  
* generator
+
{| class="wikitable"
**; MobileSubstrate
+
|-
**: generate code that uses [[MobileSubstrate]] for hooking.
+
! Key
**; internal
+
! Values
**: generate code that uses only internal Objective-C runtime methods for hooking.
+
! Notes
* warnings
+
|-
**; none
+
| rowspan="2" | generator
**: suppress all warnings
+
| MobileSubstrate
**; default
+
| generate code that uses [[MobileSubstrate]] for hooking.
**: non-fatal warnings
+
|-
**; error
+
| internal
**: make all warnings fatal
+
| generate code that uses only internal Objective-C runtime methods for hooking.
* dump
+
|-
**; yaml
+
| rowspan="3" | warnings
**: dump the internal parse tree in YAML format
+
| none
**; <strike>perl</strike>
+
| suppress all warnings
**: <strike>dump the internal parse tree in a format suitable for evaluation as perl source.</strike><br /> dump to the perl source feature is removed since [https://github.com/DHowett/theos/commit/a05354a7b9839a5dce48f7c07114f30dd195b537 this commit].
+
|-
 +
| default
 +
| non-fatal warnings
 +
|-
 +
| error
 +
| make all warnings fatal
 +
|-
 +
| rowspan="2" | dump
 +
| yaml
 +
| dump the internal parse tree in YAML format
 +
|-
 +
| <strike>perl</strike>
 +
| <strike>dump the internal parse tree in a format suitable for evaluation as perl source.</strike><br /> dump to the perl source feature is removed since [https://github.com/DHowett/theos/commit/a05354a7b9839a5dce48f7c07114f30dd195b537 this commit].
 +
|}
  
==== %ctor ====
+
=== %ctor ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 171: Line 184:
 
Generate an anonymous constructor (of default priority).
 
Generate an anonymous constructor (of default priority).
  
==== %dtor ====
+
=== %dtor ===
  
Generate a deconstructor
+
<source lang="logos">
 +
%dtor { … }
 +
</source>
  
=== Function level ===
+
Generate an anonymous deconstructor (of default priority).
 +
 
 +
== Function level ==
  
 
The directives in this category should only exist within a function block.
 
The directives in this category should only exist within a function block.
  
==== %init ====
+
=== %init ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 205: Line 222:
 
</source>
 
</source>
  
==== %class ====
+
=== %class ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 215: Line 232:
 
Forward-declare a class. Outmoded by <tt>[[Logos#.25c|%c]]</tt>, but still exists. Creates a $Class variable, and initializes it with the "_ungrouped" group.
 
Forward-declare a class. Outmoded by <tt>[[Logos#.25c|%c]]</tt>, but still exists. Creates a $Class variable, and initializes it with the "_ungrouped" group.
  
==== %c ====
+
=== %c ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 223: Line 240:
 
Evaluates to <tt>Class</tt> at runtime. If the + sigil is specified, it evaluates to MetaClass instead of Class. If not specified, the sigil defaults to -, evaluating to Class.
 
Evaluates to <tt>Class</tt> 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 ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 232: Line 249:
 
Call the original hooked method. Doesn't function in a <tt>[[Logos#.25new|%new]]</tt>'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 <tt>self</tt> and <tt>_cmd</tt>, Logos does this for you.
 
Call the original hooked method. Doesn't function in a <tt>[[Logos#.25new|%new]]</tt>'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 <tt>self</tt> and <tt>_cmd</tt>, Logos does this for you.
  
==== %log ====
+
=== %log ===
  
 
<source lang="logos">
 
<source lang="logos">
Line 241: Line 258:
 
Dump the method arguments to syslog. Typed arguments included in <tt>%log</tt> will be logged as well.
 
Dump the method arguments to syslog. Typed arguments included in <tt>%log</tt> will be logged as well.
  
== File Extensions for Logos ==
+
= File Extensions for Logos =
  
 
{| class="wikitable"
 
{| class="wikitable"
Line 263: Line 280:
 
xi or xmi files can use Logos directives in #define macros.
 
xi or xmi files can use Logos directives in #define macros.
  
== Splitting Logos Hooking Code Across Multiple Files ==
+
= 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.<br>
 
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.<br>
 
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.
 
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.
  
== logify.pl ==
+
= logify.pl =
  
 
You can use logify.pl to create a Logos source file from a header file that will log all of the functions of that header file. Here is an example of a very simple Logos tweak generated by logify.pl
 
You can use logify.pl to create a Logos source file from a header file that will log all of the functions of that header file. Here is an example of a very simple Logos tweak generated by logify.pl
Line 305: Line 322:
 
%end
 
%end
 
</source>
 
</source>
 +
 +
= External links =
 +
 +
* [https://github.com/DHowett/theos/blob/master/bin%2Flogos.pl main logos file].
 +
* [https://github.com/DHowett/theos/blob/master/bin%2Flogify.pl logify.pl]
  
 
[[Category:Development Tools]]
 
[[Category:Development Tools]]

Revision as of 17:45, 21 December 2015

Logos is a component of the Theos development suite that allows method hooking code to be written easily and clearly, using a set of special preprocessor directives.

Overview

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.

Getting Logos

Logos is distributed with Theos, and you can use Logos' syntax in any Theos-built project without any extra setup. For more information about Theos, visit its page.

List of Logos Directives

Block-level

The directives in this category open a block of code which must be closed by an %end directive (shown below). These should not exist within functions or methods.

%group

%group Groupname

Begin a hook group (for conditional initialization or code organization) with the name Groupname. All ungrouped hooks are in the implicit "_ungrouped" group.

Grouping can be used to manage backwards compatibility with older code:

%group iOS8
%hook IOS8_SPECIFIC_CLASS
	// your code here
%end // end hook
%end // end group ios8

%group iOS9
%hook IOS9_SPECIFIC_CLASS
	// your code here
%end // end hook
%end // end group ios9

%ctor {
	if (kCFCoreFoundationVersionNumber > 1200) {
		%init(iOS9);
	} else {
		%init(iOS8);
	}
}

%hook

%hook Classname

Open a hook block for the class named Classname.

Can be inside a %group block.

Here's a trivial example:

%hook SBApplicationController
-(void)uninstallApplication:(SBApplication *)application {
	NSLog(@"Hey, we're hooking uninstallApplication:!");
	%orig; // Call the original implementation of this method
	return;
}
%end

%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 generated.

Can be inside a %group block.

%subclass

%subclass Classname: Superclass <Protocol list>

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.

Here's an example:

%subclass MyObject : NSObject

- (id)init {
	self = %orig;
	[self setSomeValue:@"value"];
	return self;
}

//the following two new methods act as `@property (nonatomic, retain) id someValue;`
%new
- (id)someValue {
	return objc_getAssociatedObject(self, @selector(someValue));
}

%new
- (void)setSomeValue:(id)value {
	objc_setAssociatedObject(self, @selector(someValue), value, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

%end

%ctor {
	MyObject *myObject = [[%c(MyObject) alloc] init];
	NSLog(@"myObject: %@", [myObject someValue]);
}

%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(Key=Value);

Set a logos configuration flag.

Configuration Flags

Key Values Notes
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
perl dump the internal parse tree in a format suitable for evaluation as perl source.
dump to the perl source feature is removed since this commit.

%ctor

%ctor {  }

Generate an anonymous constructor (of default priority).

%dtor

%dtor {  }

Generate an anonymous deconstructor (of default priority).

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. The class name replacement is specially useful for classes that contain characters that can't be used as the class name token for the %hook directive, such as spaces and dots.

Usage:

%group SomeGroup
%hook SomeClass
-(id)init {
    return %orig;
}
%end
%end

%ctor {
    %init(SomeGroup,SomeClass=objc_getClass("class with spaces in the name"));
}

%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.

%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.

logify.pl

You can use logify.pl to create a Logos source file from a header file that will log all of the functions of that header file. Here is an example of a very simple Logos tweak generated by logify.pl

Given a header file:

@interface SSDownloadAsset : NSObject
- (NSString *)finalizedPath;
- (NSString *)downloadPath;
- (NSString *)downloadFileName;
+ (id)assetWithURL:(id)url type:(int)type;
- (id)initWithURLRequest:(id)urlrequest type:(int)type;
- (id)initWithURLRequest:(id)urlrequest;
- (id)_initWithDownloadMetadata:(id)downloadMetadata type:(id)type;
@end

You can find logify.pl at $THEOS/bin/logify.pl and you would use it as so:

$THEOS/bin/logify.pl ./SSDownloadAsset.h

The resulting output should be:

%hook SSDownloadAsset
- (NSString *)finalizedPath { %log; NSString * r = %orig; NSLog(@" = %@", r); return r; }
- (NSString *)downloadPath { %log; NSString * r = %orig; NSLog(@" = %@", r); return r; }
- (NSString *)downloadFileName { %log; NSString * r = %orig; NSLog(@" = %@", r); return r; }
+ (id)assetWithURL:(id)url type:(int)type { %log; id r = %orig; NSLog(@" = %@", r); return r; }
- (id)initWithURLRequest:(id)urlrequest type:(int)type { %log; id r = %orig; NSLog(@" = %@", r); return r; }
- (id)initWithURLRequest:(id)urlrequest { %log; id r = %orig; NSLog(@" = %@", r); return r; }
- (id)_initWithDownloadMetadata:(id)downloadMetadata type:(id)type { %log; id r = %orig; NSLog(@" = %@", r); return r; }
%end

External links