[ug-bosug] Fwd: [developer] HEADS-UP: illumos will now build with GCC 4.4.4 + patches

[Moinak Ghosh]

Interesting stuff. This is a milestone for a truly open Illumos. An open
toolchain is critical to an open platform.
I was against using SUN Studio for anything other than the OS itself.
Looks like now that requirement has been cleared as well.

Regards,
Moinak.

---------- Forwarded message ----------
From: Richard Lowe <rich...@richlowe.net>
Date: Fri, Jun 15, 2012 at 11:33 PM
Subject: [developer] HEADS-UP: illumos will now build with GCC 4.4.4 + patches
To: deve...@lists.illumos.org



If you don't build illumos, or don't care about how you build illumos you can
safely ignore this message.  If you contribute to illumos please do read this.

## Summary

With the integration of 1450 "Illumos should be buildable with GCC 4"
illumos may now be built with a patched version of GCC 4.4.4.  It is
neither the default compiler, nor the default shadow compiler at
present.

The patched GCC is available from:

- source:  https://github.com/richlowe/gcc/tarball/gcc-4.4.4-il-2
- x86:     http://richlowe.openindiana.org/~richlowe/il-gcc-444-i386.tar.bz2
- sparc:   http://richlowe.openindiana.org/~richlowe/il-gcc-444-sparc.tar.bz2

The binaries expect to be in /opt/gcc/4.4.4

As far as distributions go I believe the current state is this:

- SmartOS makes its own arrangements, and has been using this work for a while
- OmniOS does not make it available
- OpenIndiana are in the process of making it available, I think

## How to use it

This is not another shadow compiler, nor is it a general build-time knob
(though it may be used as one, with minor env file changes on your
part).  This is instead a means to change the version of GCC which is
used in general.

There are several variables which control this:

__GNUC - Influences whether GCC is the primary or shadow compiler, as
always.

The following are new:

__GNUC3 - The default, indicates that the version of GCC to be used is the
patched GCC 3.4 commonly found in /usr/sfw

__GNUC4 - Indicates that the version of GCC to be used is the patched GCC
4.4.4.

GCC_ROOT - The path to the prefix to which the patched GCC was
installed (defaults to /usr/sfw for GCC 3, and /opt/gcc/4.4.4 for
GNUC4).  This separates the path to GCC from the old GNU_ROOT used to
find binutils, if you were customizing GNU_ROOT, you should now
customize both GNU_ROOT and GCC_ROOT.

Thus, if you want to build with Sun Studio, but GCC 4.x as the shadow your
environment file should contain:

   GCC_ROOT=/where/you/put/gcc
   __GNUC4=""

If you want to use GCC4 as the primary compiler, it should contain:

   GCC_ROOT=/where/you/put/gcc
   __GNUC=""
   __GNUC4=""

This is not a trivial toggle.  Tools built for GCC 4 will use GCC 4 by
default, if you need to override this (to toggle quickly back and forth
between GCC 3 and GCC 4, for instance) you must also set CW_GCC_DIR to
the directory containing the gcc binary in question, so that your
existing build tools will use the GCC in question, while re-building
themselves.

### Fix your closed-bins

There's an important catch here.  As is the case with GCC 3, the closed kernel
modules which had their CTF information merged against the June 2010 genunix
will need that CTF information removed to avoid causing problems for both
DTrace and mdb.

You can do this by running 'mcs -d -n .SUNW_ctf <file>' for each closed kernel
module.  The most important ones are klmmod, klmops and mpt, which
cause problems for DTrace, however anything derived from the CTF of any
_other_ closed module will also be incorrect.  You may want to remove the CTF
from all of your (kernel) closed binaries (you should keep a pristine copy, if
you do this.)

### Building old source on top of these bits will fail

Due to bug 2860 "tools elfsign uses erroneous mix of headers", building
sources prior to this putback on a build machine running bits from this
putback or later will fail.  This is unavoidable.  Sorry.

## If you're an illumos developer

I'd really appreciate it if you started using GCC 4 in place of GCC 3
(as would downstream people already defaulting to GCC 4).

There is a plan, at some time in the possibly near future, to make GCC 4 the
default version of gcc (used, by default, as the shadow compiler).  We're
waiting on its easy availability from distributions, and that's not
_necessarily_ a hard precondition.

At present, until the default changes, it is likely best that you
continue to use GCC 3 for your RTIs, on the principle that we really
don't want _either_ build to break, but we want the default
configuration to break the least.

If you break the GCC 3 shadow build, you will be backed out.  If you
break the GCC 4 shadow build, you'll probably just be asked to fix it
(or I'll fix it).

### You will see build noise as you switch between primary compilers

Because each compiler has its own set of private symbols which get
inserted into built objects, you're going to see a lot of ELF runtime
noise as you switch between primary compilers.  It is in your interests
to make sure these builds are separate from any which could legitimately
cause runtime noise (and to try to avoid letting this noise into RTIs,
where it's very annoying to sift).

Thanks,

-- Rich


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