Re: darwin LTO broken under Xcode 3.2.6/4.0

[Ian Lance Taylor <iant at google dot com>]

Jack Howarth <howarth@bromo.med.uc.edu> writes:

>    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.

We no longer use libelf on any system.

This is largely controlled by the simple-object interface.  It should be
straightforward to change the way that simple-object works with Mach-O
without changing the simple-object interface to the rest of gcc.  Then
we could change the gcc output to, e.g., put all the information in a
single Mach-O section.

I suppose we should first ask Apple why they made the change and whether
it was intentional.

Ian