Re: GNUstep + libobjc2 and powerpc ( was "libobjc2 on powerpc")

[Josh Freeman]

On Mar 21, 2018, at 9:43 AM, David Chisnall wrote:

> > 4. The script on the wiki builds and install gnustep-make two times :
> > before and after libobjc2 ? Is it still correct ?
>
> No, that’s definitely wrong.  It dates back to when I tried to use  
> GNUstep Make to build libobjc2, but that led to circular dependencies.

   The reason for installing gnustep-make twice is that libobjc2's  
install path depends on whether gnustep-config is present (at least on  
Debian/Ubuntu): If gnustep-config is present, libobjc2 installs to / 
usr/GNUstep/Local/Library/ - if not, it installs to /usr/local/lib/.

  GNUstep-make's configure won't find libobjc2 in /usr/local/lib/;  
It'll still successfully configure ("checking for custom shared objc  
library... NONE"), build, & install, but then GNUstep-base will fail  
to build - its configure will fail the "checking whether objc really  
works..." test because no runtime was found.

  So, GNUstep make's first (pre-libobjc2) install puts gnustep-config  
in place so that libobjc2 will install in a location where GNUstep  
make's second, post-libobjc2 install can find & use it as the runtime.


> > 5. For gnustep-make build, is this line still mandatory ?
> > "git checkout `git rev-list -1 --first-parent --before=2017-04-06
> > master` # fixes segfault, should probably be looked at."
> >
> > Has this bug in gnustep-make been fixed since 2017-04-06
>
> I can’t speak for Ubuntu, but that definitely isn’t needed on FreeBSD.

   That line was added as a workaround for an issue that caused all  
apps (on Debian/Ubuntu) to segfault. The issue turned out to be  
incorrect instance-variable offsets when using libobjc2's nonfragile- 
abi.

   The reason the script's git-checkout command fixes the crashes is  
that until 2017-04-06, gnustep-make's build flag for setting the  
nonfragile-abi was in the wrong place, so gnustep-make builds ended up  
using the fragile-abi (incorrect abi, but no crashes); When a gnustep- 
make fix for the nonfragile-abi flag was checked in on 2017-04-07,  
builds started using the correct abi, and the crashes appeared. (The  
libobjc2 ivar-offset bug was already present before then, but it was  
hidden due to using the fragile-abi).

   I posted a libobjc2 patch awhile back with a workaround, and an  
updated Ubuntu script that installs the patch & can then use the  
current gnustep-make from the trunk (rolling it back to 2017-04-06 no  
longer needed). As far as I know, that patch & script are currently  
the only way to install GNUstep on Debian/Ubuntu so that it uses the  
nonfragile-ABI (until a fix is checked into clang). This bug report  
has some more info:
https://github.com/gnustep/libobjc2/issues/52

Cheers,

Josh