STABLE clang planned update MFC path (3.4.1 STABLE, 3.7.0, CURRENT) vs. powerpc64

[Mark Millard]

On 2014-Oct-11 Dimitry Andric wrote:

> On 11 Oct 2015, at 14:05, Piotr Kubaj <pkubaj at riseup.net
> > wrote:
> >
> > AFAIK if there had been such plans, they were dropped long ago. The
> > reasoning it can't be done (at least for now) is that versions 3.5.0+
> > require C++11-capable stack and that would break upgrades from 9-STABLE
> > (if the user still uses GCC, as is by default). So, LLVM in stable/10
> > will probably be upgraded when stable/9 goes EOL.
> 
> 
> If stable/10 had clang 3.5 or higher, you could still upgrade from
> stable/9.  It would only require you to do the upgrade in two steps:
> 
> * Rebuild and reinstall your stable/9 world using WITH_CLANG,
>   WITH_CLANG_IS_CC, and WITH_LIBCPLUSPLUS.  This will install clang
>   3.4.1 and libc++, and make clang the default compiler.
> * Checkout stable/10 (or even head), and build/install it in the regular
>   fashion.
> 
> I am personally not against merging newer llvm/clang versions into
> stable/10.  But the "silent agreement" has always been that you could
> upgrade easily from the latest stable/X to stable/X+1, and the above
> two-step process breaks that, or at least makes it more complicated.
> 
> Last but not least, note that this would only apply to the architectures
> that *can* actually build clang 3.4.1 and libc++ on stable/9.  This is
> currently limited to x86, little-endian arm and powerpc (64 bit, I'm
> unsure about 32 bit).
> 
> -Dimitry

lib/csu/powerpc64/Makefile in head has updates and comments (2015-Feb-05 or so) about "powerpc64 csu needs to be built by gcc, so enforce that". It is tied to clang not supporting -mlongcall and "testing shows a clang linked with a [#] clang-built csu segfaults". The forcing of gcc use in head looks like:

CC:=            gcc
COMPILER_TYPE:= gcc

which is not in stable/10's variant.

stable/10 has a lib/csu/powerpc64/Makefile that does not force gcc but still has:

CFLAGS+=        -I${.CURDIR}/../common \
                -I${.CURDIR}/../../libc/include \
                -mlongcall

and so has -mlongcall in use on the command lines. Unless -mlongcall support used to be in place for clang and was later removed, a rebuilding of FreeBSD 9 or 10 that includes a lib/csu/powerpc64/ rebuild likely fails to build under WITH_CLANG_IS_CC.

I'm not sure about going all the way back to FreeBSD 9 but this suggests that clang was for some time --and recently has been-- insufficient on its own for reliable(?) powerpc64 builds (2015-Feb-05). It may be best to consider powerpc64 omitted from the "clang 3.4.1 and libc++" list in that last paragraph given the "upgrade easily" context intended.

(If there is an easy powerpc64 upgrade then I'd like to see notes about it: Other contexts might be able to use similar techniques. I started my explorations with 10.)

===
Mark Millard
markmi at dsl-only.net