Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Matthew Cline]

First off, I've never tried to create a new thread from an existing
one, so please excuse me if I screwed up the threading, etc.

On 11/21/05, Neil Bothwick <neil@digimed.co.uk> wrote:
> You can change
> everything after a stage 3 install, although you have to be careful when
> changing CHOST.

I've just completed a stage3 install, and I'd like to change the CHOST
from "i386-pc-linux-gnu" to "i586-pc-linux-gnu". I planned to do
something like this:

1. change CHOST
2. emerge gcc gcc-config binutils glibc
3. env-update && source /etc/profile
4. use gcc-config to switch to new compiler
5. emerge gcc gcc-config binutils glibc
6. emerge -e system

Are there any additional precautions/steps that I should take?

Thanks in advance,

Matt

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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Alexander Skwar]

Matthew Cline schrieb:

> I've just completed a stage3 install, and I'd like to change the CHOST
> from "i386-pc-linux-gnu" to "i586-pc-linux-gnu".

Why? What do you expect to gain?

Alexander Skwar
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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Neil Bothwick]

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On Tue, 22 Nov 2005 07:06:01 +0100, Alexander Skwar wrote:

> > I've just completed a stage3 install, and I'd like to change the CHOST
> > from "i386-pc-linux-gnu" to "i586-pc-linux-gnu".
> 
> Why? What do you expect to gain?

A broken system :(

After changing CHOST you must run fix_libtool_files.sh.


-- 
Neil Bothwick

"A hundred years of forgetting and it all comes rushing back..."

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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Matthew Cline]

On 11/22/05, Alexander Skwar <listen@alexander.skwar.name> wrote:
>
> Why? What do you expect to gain?
>

The computer I am installing this on is an old Compaq laptop with a
Cyrix MediaGX processor. Everything I have read suggests that this is
equivalent to an i586.

Am I wrong in thinking that the CHOST variable should reflect the kind
of processor in the machine? Wouldn't leaving the CHOST at
"i386-pc-linux-gnu" build unoptimized binaries?


Matt

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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Matthias Langer]

On Tue, 2005-11-22 at 17:11 -0500, Matthew Cline wrote:
> On 11/22/05, Alexander Skwar <listen@alexander.skwar.name> wrote:
> >
> > Why? What do you expect to gain?
> >
> 
> The computer I am installing this on is an old Compaq laptop with a
> Cyrix MediaGX processor. Everything I have read suggests that this is
> equivalent to an i586.
> 
> Am I wrong in thinking that the CHOST variable should reflect the kind
> of processor in the machine? Wouldn't leaving the CHOST at
> "i386-pc-linux-gnu" build unoptimized binaries?
> 
> 
> Matt
> 

I'm not an expert, but this is just copied and pasted from the gentoo
handbook:

The CHOST variable declares the target build host for your system. This
variable should already be set to the correct value. Do not edit it as
that might break your system. If the CHOST variable does not look
correct to you, you might be using the wrong stage3 tarball.

Cheers, Matthias



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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Richard Fish]

On 11/22/05, Matthias Langer <mlangc@gmx.at> wrote:
> On Tue, 2005-11-22 at 17:11 -0500, Matthew Cline wrote:
> > On 11/22/05, Alexander Skwar <listen@alexander.skwar.name> wrote:
> > >
> > > Why? What do you expect to gain?
> > >
> >
> > The computer I am installing this on is an old Compaq laptop with a
> > Cyrix MediaGX processor. Everything I have read suggests that this is
> > equivalent to an i586.
> >
> > Am I wrong in thinking that the CHOST variable should reflect the kind
> > of processor in the machine? Wouldn't leaving the CHOST at
> > "i386-pc-linux-gnu" build unoptimized binaries?
> >
> >
> > Matt
> >
>
> I'm not an expert, but this is just copied and pasted from the gentoo
> handbook:
>
> The CHOST variable declares the target build host for your system. This
> variable should already be set to the correct value. Do not edit it as
> that might break your system. If the CHOST variable does not look
> correct to you, you might be using the wrong stage3 tarball.
>
> Cheers, Matthias

AFAICT, CHOST is (mostly) used by portage for the "--host" argument to
the autoconf scripts, which in turn uses it to determine the path for
the tool chain.  So having CHOST=i386-blah-blah means you are using
the tool chain /usr/bin/i386-blah-blah-*.

This is also the _default_ host that gcc will build code for.  So
without any -march/-mcpu/-mtune settings in CFLAGS, you will get i386
code.  However, you can override that in CFLAGS, so that gcc produces
i586 code by default (if that is what you want).

AFAIK, there should be no difference in code produced by
"i586-pc-linux-gnu-gcc" and "i386-pc-linux-gnu-gcc -march=i586".  If
there is, then things like distcc should be horribly broken.

-Richard

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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Richard Fish]

On 11/22/05, Richard Fish <bigfish@asmallpond.org> wrote:
> AFAIK, there should be no difference in code produced by
> "i586-pc-linux-gnu-gcc" and "i386-pc-linux-gnu-gcc -march=i586".  If
> there is, then things like distcc should be horribly broken.

Well, I've been following a related thread on gentoo-dev, and it seems
I am wrong with regards to building glibc.  CHOST is much more
important for glibc, leading to the support (or lack thereof) of
things like nptl.

http://bugs.gentoo.org/show_bug.cgi?id=106556

So for getting a completely compatible i586 install, you may have to
risk changing CHOST, since there is no i586 tarball available.

-Richard

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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Alexander Skwar]

Matthew Cline schrieb:

> Am I wrong in thinking that the CHOST variable should reflect the kind
> of processor in the machine?

Yes.

> Wouldn't leaving the CHOST at
> "i386-pc-linux-gnu" build unoptimized binaries?

No.

Alexander Skwar
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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Robin]

> > Wouldn't leaving the CHOST at
> > "i386-pc-linux-gnu" build unoptimized binaries?
>
> No.
>
> Alexander Skwar

Thanks for that. My CHOST flag is set to i386-pc-linux-gnu even though
it is not.  Just a piece of mind I guess not building unoptimized
binaries.

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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[W.Kenworthy]

To explain, keep in mind that optimisation and chost are two different
things.  

i386 is a "lowest common denominator" instruction set that will run on
most 386 and above x86 processors.  i4/5/686 adds few specialised
instructions and I believe the compiler is able to use them to produce
faster code in some cases.  The downside is the loss of compatibility -
apparent if you switch processors.  Is the system faster - my tests
(done ages ago now) say yes, but not by much and its highly dependent on
the actual code/data in use at the time.  

Generally, you will get more gain by smarter configuration, better
software etc.  Thats not to say optimised CFLAGS and compiler choices
wont give a useful speedup, especially when crunching data.  It just
wont turn a 667Mhz P3 into the equivalent 1G P3 - I know I recently
tried to "get a little more" out of one :)

BillK

On Wed, 2005-11-23 at 21:24 -0400, Robin wrote:
> > > Wouldn't leaving the CHOST at
> > > "i386-pc-linux-gnu" build unoptimized binaries?
> >
> > No.
> >
> > Alexander Skwar
> 
> Thanks for that. My CHOST flag is set to i386-pc-linux-gnu even though
> it is not.  Just a piece of mind I guess not building unoptimized
> binaries.
> 
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Re: changing CHOST in stage3 (was : [gentoo-user] default stage3)

[Ciaran McCreesh]

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On Mon, 21 Nov 2005 21:08:40 -0500 Matthew Cline
<matthew.cline@gmail.com> wrote:
| On 11/21/05, Neil Bothwick <neil@digimed.co.uk> wrote:
| > You can change
| > everything after a stage 3 install, although you have to be careful
| > when changing CHOST.
| 
| I've just completed a stage3 install, and I'd like to change the CHOST
| from "i386-pc-linux-gnu" to "i586-pc-linux-gnu". I planned to do
| something like this:
<snip>
| Are there any additional precautions/steps that I should take?

The only way you can safely change CHOST is by making new stages
through catalyst. There're various scripts which *sometimes* fix your
system after a CHOST change, but they're not reliable...

-- 
Ciaran McCreesh : Gentoo Developer (Look! Shiny things!)
Mail            : ciaranm at gentoo.org
Web             : http://dev.gentoo.org/~ciaranm


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[gentoo-user] Re: changing CHOST in stage3

[Allan Gottlieb]

At Tue, 22 Nov 2005 13:17:27 +0000 Ciaran McCreesh <ciaranm@gentoo.org> wrote:

> The only way you can safely change CHOST is by making new stages
> through catalyst. There're various scripts which *sometimes* fix your
> system after a CHOST change, but they're not reliable...

Does this mean that, if one needs a CHOST value not represented in any
of the current stage3 tar files, your recommendation would be to begin
with a stage1?

thanks,
allan
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Re: [gentoo-user] Re: changing CHOST in stage3

[Ciaran McCreesh]

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On Wed, 23 Nov 2005 15:34:27 -0500 Allan Gottlieb <gottlieb@nyu.edu>
wrote:
| At Tue, 22 Nov 2005 13:17:27 +0000 Ciaran McCreesh
| <ciaranm@gentoo.org> wrote:
| > The only way you can safely change CHOST is by making new stages
| > through catalyst. There're various scripts which *sometimes* fix
| > your system after a CHOST change, but they're not reliable...
| 
| Does this mean that, if one needs a CHOST value not represented in any
| of the current stage3 tar files, your recommendation would be to begin
| with a stage1?

Nope. You need a stage3 to build a stage1 with a new CHOST.

-- 
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Mail            : ciaranm at gentoo.org
Web             : http://dev.gentoo.org/~ciaranm


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Re: [gentoo-user] Re: changing CHOST in stage3

[Allan Gottlieb]

At Thu, 24 Nov 2005 04:58:07 +0000 Ciaran McCreesh <ciaranm@gentoo.org> wrote:

> On Wed, 23 Nov 2005 15:34:27 -0500 Allan Gottlieb <gottlieb@nyu.edu>
> wrote:
> | At Tue, 22 Nov 2005 13:17:27 +0000 Ciaran McCreesh
> | <ciaranm@gentoo.org> wrote:
> | > The only way you can safely change CHOST is by making new stages
> | > through catalyst. There're various scripts which *sometimes* fix
> | > your system after a CHOST change, but they're not reliable...
> | 
> | Does this mean that, if one needs a CHOST value not represented in any
> | of the current stage3 tar files, your recommendation would be to begin
> | with a stage1?
>
> Nope. You need a stage3 to build a stage1 with a new CHOST.

In the faq (http://www.gentoo.org/doc/en/faq.xml#stage12) I find.

    How do I Install Gentoo Using a Stage1 or Stage2 Tarball?

    The Gentoo Handbook only describes a Gentoo installation using a
    stage3 tarball. However, Gentoo still provides stage1 and stage2
    tarballs. This is for development purposes (the Release Engineering
    team starts from a stage1 tarball to obtain a stage3) but shouldn't be
    used by users: a stage3 tarball can very well be used to bootstrap the
    system. You do need a working Internet connection.

It surprises me that release engineering starts with a stage1 to get a
stage3 and then we use this stage3 to build a stage1.  I mention this
only out of curiosity; there is a stage3 with my desired CHOST and I
expect to do all future installs starting with stage3 (I formerly used
stage1).

thanks,
allan

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Re: [gentoo-user] Re: changing CHOST in stage3

[Ciaran McCreesh]

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On Thu, 24 Nov 2005 12:48:34 -0500 Allan Gottlieb <gottlieb@nyu.edu>
wrote:
| It surprises me that release engineering starts with a stage1 to get a
| stage3 and then we use this stage3 to build a stage1.  I mention this
| only out of curiosity; there is a stage3 with my desired CHOST and I
| expect to do all future installs starting with stage3 (I formerly used
| stage1).

Well... You need a reasonably complete system to build a toolchain,
hence the stage 3 seed. Building a toolchain with a different CHOST is
pretty close to cross-compiling, so the only way you can do it safely
is to start from scratch, hence building up from a stage 1.

-- 
Ciaran McCreesh : Gentoo Developer (Supreme Lord Gerbil Wrangler)
Mail            : ciaranm at gentoo.org
Web             : http://dev.gentoo.org/~ciaranm


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Re: [gentoo-user] Re: changing CHOST in stage3

[Allan Gottlieb]

At Thu, 24 Nov 2005 19:55:03 +0000 Ciaran McCreesh <ciaranm@gentoo.org> wrote:

> On Thu, 24 Nov 2005 12:48:34 -0500 Allan Gottlieb <gottlieb@nyu.edu>
> wrote:
> | It surprises me that release engineering starts with a stage1 to get a
> | stage3 and then we use this stage3 to build a stage1.  I mention this
> | only out of curiosity; there is a stage3 with my desired CHOST and I
> | expect to do all future installs starting with stage3 (I formerly used
> | stage1).
>
> Well... You need a reasonably complete system to build a toolchain,
> hence the stage 3 seed. Building a toolchain with a different CHOST is
> pretty close to cross-compiling, so the only way you can do it safely
> is to start from scratch, hence building up from a stage 1.

Thank you for this clear explanation.
allan
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