libobjc2 message-to-nil inconsistency

[Jens Alfke]

Hi all. I’m debugging some software I’m porting from Mac OS X / iOS to GNUstep. 
Just spent an hour tracking down a problem that stems from a difference in the 
return value of a message to nil. Specifically:

        NSNumber* n = nil;
        SInt64 value = [n longLongValue];
        assert(value == 0);    // passes with Apple’s runtime, fails with 
libobjc2

In the olden days on OS X, this was a no-no because the return value of a 
64-bit message-send to nil was undefined (objc_msgsend was zeroing the return 
value in a way that worked for 32-bits or less but not for 64-bit.) However, at 
some point (10.6 I think) the dispatcher was improved to also zero the 64-bit 
return state. My code implicitly depends on this behavior.

It appears that libobjc2 still has the old behavior and does not clear the 
64-bit return value (at least not in a 32-bit process.) So I’m getting garbage 
values from -longLongValue and similar methods when the receiver is nil, which 
breaks my code. Obviously I can put nil-checks in the code, but I’m not sure 
where exactly all the places are that depend on this and need to be changed. 
There could be a lot of debugging ahead.

Is this a known issue in libobjc2? Is it something that will be fixed, or is it 
considered a difference in behavior that will remain that way?

—Jens