Re: Tutorials enhancement proposal : First Steps in GNUstep GUI Programming (2) : NSWindow, NSButton

[David Chisnall]

Hi,

I'm not sure where you get that from.  The only comment about 64-bit on 
that page is in reference to Apple's implementation, stating that the 
new ABI is the only option on 64-bit Apple platforms (Apple supported 
the old and new ABIs on 32-bit x86, only the new one on 64-bit Macs and 
only the new one on any iOS devices).

That said, the page is quite out of date.  The new runtime supports 
three ABIs:

 - The old GCC one.  Basically, don't use this, it doesn't support any 
post-2005 Objective-C features.
 - The GNUstep v1 ABI, which tried to be backwards compatible with the 
GCC runtime so you could mix code compiled with GCC.  This didn't work 
particularly well and, in hindsight, was a bad idea.  This is the 
minimum for using features like ARC.
 - The GNUstep v2 ABI, which is designed to use modern linker features. 
 This supports all modern Objective-C features.  This depends on some 
features specific to the binary format and so is supported on ELF and 
COFF platforms (not currently Mach-O or Wasm, though I'd be interested 
in adding them at some point).

ARC's memory model intrinsically requires an ABI with non-fragile 
instance variables (i.e. the generated code does not hard-code the 
offsets of instance variables, instead it looks the offsets up in a 
variable initialised by the runtime).

You control the runtime with the -fobjc-runtime= flag to clang.  The 
format is:

-fobjc-runtime={runtime name}-{version}

The options are:

gcc, any version, targets the old GCC ABI.

gnustep-1.{0-8} targets the GNUstep 1.x ABI, restricting itself to 
features supported by the corresponding runtime release, for example not 
using property accessor helpers that weren't added or only using 
objc_msgSend on architectures that have the right implementation.

gnustep-2.0 (currently the only 2.x version, any point release value is 
ignored).  This switches to the new ABI.  This should give smaller 
binaries and faster code, but is incompatible with code compiled with GCC.

ARMv7 has all of the assembly fast paths, so should work well with the 
new ABI, though I think there may still be a few corner cases in C++ 
exception interop that don't work with the ARM EH ABI.  Please try using 
libobjc2 trunk and file bug reports on GitHub as you find them!

David

On 11/06/2020 20:01, Patrick Cardona wrote:
> Hi David,
>
> I looked around to better understand how to use ARC and the new ABI as you 
> suggested.
> But according to your article on the wiki (1), I understood that only 64bits 
> systems could be able to use the new ABI : is it right ?
>
> And the RPI 3B+ I am using now is only 32 bits :
> description: ARMv7 Processor rev 4 (v7l)
>      product: Raspberry Pi 3 Model B Plus Rev 1.3
>      ...
>      bits: 32 bits
>
>
> (1) The Wiki source :
>   http://wiki.gnustep.org/index.php/ObjC2_FAQ,