Re: [PATCH] Introduce biarch DISTRO_FEATURE

[Richard Purdie <richard.purdie@linuxfoundation.org>]

On Mon, 2011-11-07 at 23:14 +0000, Julian Pidancet wrote:
> On Wed, Oct 26, 2011 at 3:09 AM, McClintock Matthew-B29882
> <B29882@freescale.com> wrote:
> > On Mon, Oct 24, 2011 at 8:18 PM, Julian Pidancet
> > <julian.pidancet@gmail.com> wrote:
> >> This patch introduces a distro feature which enables gcc to produce
> >> both 32bit and 64bit code, and enables binutils to operate on both
> >> 32bit and 64bit binaries. It differs from multilib toolchains in
> >> that it does not require to compile a version of the libc for each
> >> architecture variant. However, the code produced for the secondary
> >> architecture will not be linkable against the libc.
> >>
> >> This patch only works with x86 and x86_64 architectures, but can
> >> probably be extended to support other architectures as well.
> >>
> >> One use-case would be when one wants to compile a system which runs
> >> 32bit userspace applications with a 64bit kernel without having to
> >> deal with two separate libc.
> >
> > What happens with the native gcc on the root file system. And what
> > about meta-toolchain? Any effect?
> >
> 
> Hi Matthew, sorry for the late answer.
> 
> I'm affraid I don't quite see what you mean by "the native gcc on the
> root file system". Are you refering to the version of GCC present on
> the build machine and built by OE ? Or are you refering instead about
> a potential version of GCC running on the target ?
> 
> This patch should only make gcc-cross, and gcc running on the target
> "biarch". It would also probably make sense to build a biarch GCC in
> the meta-toolchain case.
> 
> To be honest, I have not really considered the meta-toolchain case as
> I've never used it before and not quite sure how it works.
> 
> I can respin a patch to handle the meta-toolchain case. But in the
> mean-time, it would be nice if I could get an opinion on wether this
> "biarch" feature is a good idea or not, or, if not, maybe some
> suggestions about how to address this specific 32bit/64bit use-case
> differently.

I'm left wondering how useful the resulting compiler is to most users.
In most cases a user would expect full libc support and hence this is
likely to confuse them. I do appreciate people do have usecases for a
compiler that can handle the other bit format though.

I think my biggest worry is the "--enable-targets=all" option which may
or may not enable things we might not want enabled. I've not had a
chance to go and look at gcc and convince myself that piece is safe. The
other pieces looked less worrying.

Cheers,

Richard