On Sun, Mar 13, 2011 at 11:19:13AM -0700, Chris Lattner wrote:
>
> 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.
>
> -Chris
Chris,
Is there any documentation or example code on how to properly use
subsections in mach-o?
My fear is that we are moving from one poorly documented technique to another
which may well
have it own slate of hidden bugs.
Jack
