Function hooking in Swift
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Function hooking in Swift
1–9 of 9 posts
Re: Function hooking in Swift
#2Very interesting write-up, thanks! Makes me want to get back into C programming :) How did you manage to learn all of this stuff, for a new, closed-source and relatively undocumented (e.g. @asmname) language?
Re: Function hooking in Swift
#3Boo. Hoo.
Re: Function hooking in Swift
#4Very interesting write-up, thanks! Makes me want to get back into C programming :) How did you manage to learn all of this stuff, for a new, closed-source and relatively undocumented (e.g. @asmname) language?
It's all about reverse-engineering stuff; my usual workflow looks like:
(1) Complile some Swift program & look at the disasembler listing of it (I use IDA and — for Objective-C — Hopper Disassembler);
(2) Do some changes in source code in the program, compile it again, and see diffs in disassembler listing;
that way I can see what is changed and how.
About the @asmname thing: you can easily dump every default Swift module using a REPL command:
repl> :print_module Swift
There you can find a lot of interesting language lexems and more, so all you have to do is to try using them in your code until you don't figure it out ;)
Re: Function hooking in Swift
#5The "function trampoline" that's described looks more or less like the Block ABI. Some good learning is available in the source for `libclosure`, [Language Specification for Blocks](http://www.opensource.apple.com/source/libclosure/libclosure...) and [Block Implementation Specification](http://www.opensource.apple.com/source/libclosure/libclosure...).
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Consistently being able to hook functions in Swift is going to be a pain in release mode optimizations, as the Swift compiler does aggressive inlining.
Re: Function hooking in Swift
#6I know its a new language, but does every blog post about Swift now need to show up on HN front page? I thought it was bad for "anything JS related" posts here.
Re: Function hooking in Swift
#7const char type:1; // I'm not sure about this and padding,
char padding[7]; // maybe it's just a uint64_t too...
This is for struct alignment to address boundaries. It's fairly typical C and results in some performance optimizations.
Re: Function hooking in Swift
#8I've seen this concern that there are no function pointers in swift, and it seems to come from a misunderstanding on what it means for functions to be first class.
From https://developer.apple.com/library/prerelease/ios/documenta... :
You use function types just like any other types in Swift. For example, you can define a constant or variable to be of a function type and assign an appropriate function to that variable:
var mathFunction: (Int, Int) -> Int = addTwoInts
mathFunction can now be passed around, fed in as a parameter in another function, etc. mathFunction is for all purposes a function pointer.
Re: Function hooking in Swift
#9I've seen this concern that there are no function pointers in swift, and it seems to come from a misunderstanding on what it means for functions to be first class. From https://developer.apple.com/library/prerelease/ios/documenta... : You use function types just like any other types in Swift. For example, you can define a constant or variable to be of a function type and assign an appropriate function to that variabl…
Well, there isn't any C-style function pointer (means you can not get it's raw address in memory to do something with it), but yeah — you can pass functions as arguments.