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,
It appears this change is highly unlikely to be fixed. Chris Lattner said...
> Jack, various datastructures in the toolchain and the .o file only store the
> section number as a byte.
> Allowing it to overflow just masks bugs because section id's will be silently
> truncated. You
> should fix the GCC LTO model to store one big section with its own
> subcontents if you want more granularity.
So lto-object.c needs a rewrite to use only a single section for GNU_LTO with
subsections.
Unfortunately I can't find any documentation for using subsections in mach-o
which may imply we will
be forced to use an elf container to obtain those, no?
Jack
> > Jack
