[gentoo-user] Changing CFLAGS

[gentoo-user] Changing CFLAGS

[Alex Schuster]

Hi there!

My motherboard or CPU just died, I am using a replacement system 
for a while. It's an Athlox-XP, while I had an AMD-64 before.
I did not use 64 bit mode, but I have -march=k8 in my CFLAGS, 
and get lots of illegal instructions. Seems I need to re-compile
everything with different CFLAGS, maybe -mcpu=k8 maybe this time 
as I am planning to re-activate the old system some time.

What would be the best way to do this? I thought about unpacking
a stage1 tarball, changing CFLAGS, calling bootstrap.sh and doing
an emerge -e world, but this would overwrite things in /etc and 
clutter my file system with more things I do not really want, 
like creating entries in /dev. I would rather like to keep the
current setup as it is.

I think that I saw a howto once about what to do in such a case,
but at that time I did not need it, and now I cannot find it.


BTW: What exactly are the benefits from using march instead of 
mcpu? Is there a noticeable difference in speed anyway? With mcpu 
I would not have the trouble I am having now...

	Alex
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Re: [gentoo-user] Changing CFLAGS

[Hemmann, Volker Armin]

On Samstag, 28. April 2007, Alex Schuster wrote:

>
> What would be the best way to do this?

complete reinstallation.

> I thought about unpacking 
> a stage1 tarball, changing CFLAGS, calling bootstrap.sh and doing
> an emerge -e world, but this would overwrite things in /etc and
> clutter my file system with more things I do not really want,
> like creating entries in /dev. I would rather like to keep the
> current setup as it is.

use knoppix.
If you don't want to reinstall everything and the XP is just a temporary 
replacement, get a knoppix livecd. It lets you save things to a file, if you 
want to.
>
> I think that I saw a howto once about what to do in such a case,
> but at that time I did not need it, and now I cannot find it.

the howto is: remove the system and start from scratch.

>
>
> BTW: What exactly are the benefits from using march instead of
> mcpu? Is there a noticeable difference in speed anyway? With mcpu
> I would not have the trouble I am having now...

Your trouble started, when you switched to a completly different cpu... 

mcpu = only rearranging stuff so it might run better on the cpu specified. No 
instructions and features used, that are not available on all the other cpus 
from a family (in theory, a binary built with mcpu=athlon-xp should be able 
to run on a i486).

march = optimizing for the specified cpu. Using all features and instructions 
available, building stuff not able to run on other cpus. (so a resulting 
binary of march=athlon-xp won't run on a i486)

usually march is faster on the given cpu, mcpu is more compatible.

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[gentoo-user] Re: Changing CFLAGS

[Alexander Skwar]

· Hemmann, Volker Armin <volker.armin.hemmann@tu-clausthal.de>:
> On Samstag, 28. April 2007, Alex Schuster wrote:

>> BTW: What exactly are the benefits from using march instead of
>> mcpu? Is there a noticeable difference in speed anyway? With mcpu
[...]
> usually march is faster on the given cpu, mcpu is more compatible.

Is it noticeable, though?

Alexander Skwar
-- 
"Beware of programmers carrying screwdrivers."
-- Chip Salzenberg


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Re: [gentoo-user] Re: Changing CFLAGS

[Hemmann, Volker Armin]

On Samstag, 28. April 2007, Alexander Skwar wrote:
> · Hemmann, Volker Armin <volker.armin.hemmann@tu-clausthal.de>:
> > On Samstag, 28. April 2007, Alex Schuster wrote:
> >> BTW: What exactly are the benefits from using march instead of
> >> mcpu? Is there a noticeable difference in speed anyway? With mcpu
>
> [...]
>
> > usually march is faster on the given cpu, mcpu is more compatible.
>
> Is it noticeable, though?

well, march uses things like sse/sse2/sse3 or 3dnow and mcpu does not. So yes, 
it is.

You can test it for yourself. Get a 400mhz CPU with 3dnow, like a K6-2 or 
K6-3, and compile mplayer or xine-lib with mcpu and with march. With march 
you can watch videos. With mcpu you get a fast slideshow.
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Re: [gentoo-user] Changing CFLAGS

[Csányi András]

Hemmann, Volker Armin írta:
> the howto is: remove the system and start from scratch.
>   
uhhh...
3 days before changed I the cpu type in /etc/make.conf file and
recompile the system.
And it is work without problems...
I'm very lucky...

Best regards,
András

---sorry my english..., study ---

-- 
- -
--  Csányi András  -- http://sayusi.hu -- Sayusi Ando
--  "Bízzál Istenben és tartsd szárazon a puskaport!" -- Cromwell

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Re: [gentoo-user] Changing CFLAGS

[Ryan Sims]

On 5/3/07, Csányi András <sayusi.ando@gmail.com> wrote:
> Hemmann, Volker Armin írta:
> > the howto is: remove the system and start from scratch.
> >
> uhhh...
> 3 days before changed I the cpu type in /etc/make.conf file and
> recompile the system.
> And it is work without problems...
> I'm very lucky...

>From what to what?  Were you using march or mcpu?

-- 
Ryan W Sims
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Re: [gentoo-user] Changing CFLAGS

[Csányi András]

2007/5/4, Ryan Sims <rwsims@gmail.com>:
> On 5/3/07, Csányi András <sayusi.ando@gmail.com> wrote:
> > Hemmann, Volker Armin írta:
> > > the howto is: remove the system and start from scratch.
> > >
> > uhhh...
> > 3 days before changed I the cpu type in /etc/make.conf file and
> > recompile the system.
> > And it is work without problems...
> > I'm very lucky...
>
> From what to what?  Were you using march or mcpu?

CLAGS="-O2 -march=i686 -pipe" to
CFLAGS="-O2 -march=pentium4-m -pipe"

the machine:
Toshiba L30 Laptop

-- 
- -
--  Csanyi Andras  -- http://sayusi.hu -- Sayusi Ando
--  "Bízzál Istenben és tartsd szárazon a puskaport!".-- Cromwell

Re: [gentoo-user] Changing CFLAGS

[Csányi András]

2007/5/4, Csányi András <sayusi.ando@gmail.com>:
> 2007/5/4, Ryan Sims <rwsims@gmail.com>:
> > On 5/3/07, Csányi András <sayusi.ando@gmail.com> wrote:
> > > Hemmann, Volker Armin írta:
> > > > the howto is: remove the system and start from scratch.
> > > >
> > > uhhh...
> > > 3 days before changed I the cpu type in /etc/make.conf file and
> > > recompile the system.
> > > And it is work without problems...
> > > I'm very lucky...
> >
> > From what to what?  Were you using march or mcpu?
>
> CLAGS="-O2 -march=i686 -pipe" to
> CFLAGS="-O2 -march=pentium4-m -pipe"

Sorry... I'm tired...

CFLAGS="-O2 -march=i686 -pipe" to
CFLAGS="-O2 -march=pentium4-m -pipe"


-- 
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--  Csanyi Andras  -- http://sayusi.hu -- Sayusi Ando
--  "Bízzál Istenben és tartsd szárazon a puskaport!".-- Cromwell