Re: darwin LTO broken under Xcode 3.2.6/4.0

[Jan Hubicka <hubicka@ucw.cz>]

> 
> On Mar 13, 2011, at 8:38 AM, Jack Howarth wrote:
> 
> > On Sun, Mar 13, 2011 at 12:39:26PM +0100, Jan Hubicka wrote:
> >>>   With release of Xcode 3.2.6/4.0 this week, an unfortunate change was made to
> >>> the darwin assembler which effectively breaks LTO support for darwin. The design
> >>> of LTO on darwin was based on the fact that mach-o object files tolerated additional
> >>> sections as long as they didin't contain symbols. With Xcode 3.2.6/4.0, the assembler
> >>> appears to be strictly counting sections and objecting when these exceed 255. This
> >>> breaks huge sections of the lto testsuite and prevents larger projects like xplor-nih
> >>> to compile if Xcode 3.2.6/4.0 is installed. I am afraid that unless Apple reverts this
> >>> change, our only recourse would be to resort to an elf object container for the lto
> >>> sections within the mach-o files (introducing an undesired dependency on libelf for
> >>> FSF gcc on darwin). My understanding was that the lto design did not allow the number
> >>> of sections required in the lto files to be reduced.
> >> 
> >> If the problem is not fixed, we could always pack all the LTO sections into one section containing
> >> our own subsections.
> >> 
> >> Honza
> > 
> > Jan,
> >  If this could be done without resorting to other container types (like elf), it might be
> > the wisest approach for the long run. I've read through the mach-o documentation and it
> > seems rather vague on the section limits. Even if Apple fixes Xcode (which likley won't
> > happen for 6-9 months at best), we always we have to worry that they will break this 
> > 'feature' somewhere else in their tool chain. Better to follow the strictest possible reading
> > of mach-o object format to protect ourselves from overzealous Apple interns.
> 
> Yes, I agree that this is a better solution.  This error was put into the linker to detect some overflow conditions for part of the code that expected the section number to only be a byte.  It is likely that "things worked" only out of luck before.

Interesting, so there is no -ffunction-section type tricks at darwin?

Pickling everything into single section seems indeed like easiest approach here.
The question is who will volunteer to implement it ;)

Honza
> 
> -Chris