mikeash.com pyblog/friday-qa-2012-11-16-lets-build-objc_msgsend.html comments

no name field sorry - 2024-10-12 22:05:10

Sat, 12 Oct 2024 22:05:10 GMT

it's insane we have amazing articles like this for free!

Yue Wang - 2013-07-15 20:57:58

Mon, 15 Jul 2013 20:57:58 GMT

unused is for better memory alignment (serve as padding).

Nicolas VERINAUD - 2013-02-04 15:18:07

Mon, 04 Feb 2013 15:18:07 GMT

Here is the official source code for the assembly part behind objc messaging (for arm): https://github.com/bavarious/objc4/blob/master/runtime/Messengers.subproj/objc-msg-arm.s

Enjoy ! :P

SlashFX - 2012-12-06 03:41:00

Thu, 06 Dec 2012 03:41:00 GMT

Thanks for all your articles. They've been a big help!

mikeash - 2012-11-21 15:18:08

Wed, 21 Nov 2012 15:18:08 GMT

The iOS simulator uses i386 so you'll need to follow those rules for parameter passing and returning. Unfortunately, i386 passes parameters completely differently. Due to the relative lack of registers, it does all parameter passing on the stack, so you'll have to take a rather different approach to building the trampoline there. For more information on just how the parameter passing works, Apple spells out their i386 ABI here:

https://developer.apple.com/library/mac/#documentation/developertools/conceptual/LowLevelABI/130-IA-32_Function_Calling_Conventions/IA32.html#//apple_ref/doc/uid/TP40002492-SW4

iSofTom - 2012-11-21 10:51:57

Wed, 21 Nov 2012 10:51:57 GMT

Thanks a lot for this great article! I am trying to do the same thing for the iOS simulator, but having trouble to find out the right registers. Any clues or links ?

Simon Strandgaard - 2012-11-18 13:38:06

Sun, 18 Nov 2012 13:38:06 GMT

Awesome explanation. It's been ages I have coded any assembler. Nice.

mikeash - 2012-11-17 01:22:40

Sat, 17 Nov 2012 01:22:40 GMT

Vasi: You're right, of course. I was concentrating on my guarantees as the caller and completely forgot about my responsibilities as the callee. I've updated the code to save and restore r12. Thanks for pointing that out.

Vasi - 2012-11-16 20:27:54

Fri, 16 Nov 2012 20:27:54 GMT

Thanks for the detailed article! I think your use of %r12 isn't safe though, according to the ABI spec it's supposed to be callee-saved.

Steve Weller - 2012-11-16 16:16:00

Fri, 16 Nov 2012 16:16:00 GMT

For better compatibility with real life, I'd add a test for nil self so that messaging nil does nothing rather than crash.