[gentoo-user] downgrading gcc

[gentoo-user] downgrading gcc

[Mark Knecht]

Hi,
   Is downgrading gcc allowed within the same major version?  If I
wanted to downgrade my gcc from 4.3.2 to 4.1.2 then:

1) Do I simply choose 4.1.2 using gcc-config?

2) Should I expect any problems with the system if I do

emerge -e system
emerge -e system   [OPTIONAL]
emerge -e world

Thanks in advance,
Mark

Re: [gentoo-user] downgrading gcc

[Dale]

Mark Knecht wrote:
> Hi,
>    Is downgrading gcc allowed within the same major version?  If I
> wanted to downgrade my gcc from 4.3.2 to 4.1.2 then:
>
> 1) Do I simply choose 4.1.2 using gcc-config?
>
> 2) Should I expect any problems with the system if I do
>
> emerge -e system
> emerge -e system   [OPTIONAL]
> emerge -e world
>
> Thanks in advance,
> Mark
>
>
>   

You may also want to see my reply to the USB thread. 

Dale

:-)  :-) 

Re: [gentoo-user] downgrading gcc

[Alan McKinnon]

On Sunday 19 April 2009 22:18:24 Mark Knecht wrote:
> Hi,
>    Is downgrading gcc allowed within the same major version?  If I
> wanted to downgrade my gcc from 4.3.2 to 4.1.2 then:

It's not a problem. If it were, there would be no point in allowing multiple 
versions as it would not be possible to select a lower numbered one

> 1) Do I simply choose 4.1.2 using gcc-config?

Yes

> 2) Should I expect any problems with the system if I do
>
> emerge -e system
> emerge -e system   [OPTIONAL]
> emerge -e world

Why would you want to do this?

Do you suspect a toolchain API/ABI breakage between 4.1.2 and 4.3.2?

-- 
alan dot mckinnon at gmail dot com

Re: [gentoo-user] downgrading gcc

[Dale]

Alan McKinnon wrote:
> On Sunday 19 April 2009 22:18:24 Mark Knecht wrote:
>   
>> 2) Should I expect any problems with the system if I do
>>
>> emerge -e system
>> emerge -e system   [OPTIONAL]
>> emerge -e world
>>     
>
> Why would you want to do this?
>
> Do you suspect a toolchain API/ABI breakage between 4.1.2 and 4.3.2?
>
>   

He has been having trouble with mythtv, separate thread, and he has ran
out of other options.  He was following my thread and wants to back up
to the old version of gcc to see if that corrects his problem.  I
suspect he would need to at least do a emerge -e mythtv to test this.  I
don't have mythtv here but I suspect that would be just about everything
on his system and if gcc is causing this issue, he may as well test it
all at once.

That's the reason for what he is doing.

Dale

:-)  :-) 

Re: [gentoo-user] downgrading gcc

[Alan McKinnon]

On Monday 20 April 2009 02:05:35 Dale wrote:
> Alan McKinnon wrote:
> > On Sunday 19 April 2009 22:18:24 Mark Knecht wrote:
> >> 2) Should I expect any problems with the system if I do
> >>
> >> emerge -e system
> >> emerge -e system   [OPTIONAL]
> >> emerge -e world
> >
> > Why would you want to do this?
> >
> > Do you suspect a toolchain API/ABI breakage between 4.1.2 and 4.3.2?
>
> He has been having trouble with mythtv, separate thread, and he has ran
> out of other options.  He was following my thread and wants to back up
> to the old version of gcc to see if that corrects his problem.  I
> suspect he would need to at least do a emerge -e mythtv to test this.  I
> don't have mythtv here but I suspect that would be just about everything
> on his system and if gcc is causing this issue, he may as well test it
> all at once.
>
> That's the reason for what he is doing.

OK, so it's sort of like Windows then - when you tried everything else and 
nothing works yet, just reinstall?

I find these difficulties people are having with X somewhat amusing - my two 
personal machines have been on ~arch since forever, and even with huge amounts 
of activity in the last 18 months on X, gcc and glibc, all upgrades have been 
as smooth as silk for me.

A possibility (speaking generically now), is that X and it's drivers and a 
bunch of other stuff all need to be compile with the same gcc. nvidia is like 
this and silently barfs if you don't. It's easy to get right with an upgrade - 
go to the latest - but a downgrade is a completely different animal (you don't 
know what you should be going back to). 



-- 
alan dot mckinnon at gmail dot com

Re: [gentoo-user] downgrading gcc

[Dale]

Alan McKinnon wrote:
> On Monday 20 April 2009 02:05:35 Dale wrote:
>   
>> Alan McKinnon wrote:
>>     
>>> On Sunday 19 April 2009 22:18:24 Mark Knecht wrote:
>>>       
>>>> 2) Should I expect any problems with the system if I do
>>>>
>>>> emerge -e system
>>>> emerge -e system   [OPTIONAL]
>>>> emerge -e world
>>>>         
>>> Why would you want to do this?
>>>
>>> Do you suspect a toolchain API/ABI breakage between 4.1.2 and 4.3.2?
>>>       
>> He has been having trouble with mythtv, separate thread, and he has ran
>> out of other options.  He was following my thread and wants to back up
>> to the old version of gcc to see if that corrects his problem.  I
>> suspect he would need to at least do a emerge -e mythtv to test this.  I
>> don't have mythtv here but I suspect that would be just about everything
>> on his system and if gcc is causing this issue, he may as well test it
>> all at once.
>>
>> That's the reason for what he is doing.
>>     
>
> OK, so it's sort of like Windows then - when you tried everything else and 
> nothing works yet, just reinstall?
>
> I find these difficulties people are having with X somewhat amusing - my two 
> personal machines have been on ~arch since forever, and even with huge amounts 
> of activity in the last 18 months on X, gcc and glibc, all upgrades have been 
> as smooth as silk for me.
>
> A possibility (speaking generically now), is that X and it's drivers and a 
> bunch of other stuff all need to be compile with the same gcc. nvidia is like 
> this and silently barfs if you don't. It's easy to get right with an upgrade - 
> go to the latest - but a downgrade is a completely different animal (you don't 
> know what you should be going back to). 
>
>
>
>   

Well, this is basically what I had to do.  I wouldn't call it a complete
reinstall but it is pretty close.  It's not like booting from a CD and
starting from scratch.

In the original thread, he got a lot of help and tried a lot of things
including recompiling a lot of things from what I read.  I mentioned
this should be a last resort.  This is time consuming to say it lightly.

That said, it has worked well for me.  Everything on my rig is working
again.  If he has to do this downgrade of gcc, then a emerge -e world
and everything works again, I'm going to really wonder what the deal is
with gcc.  Just me running into problems is one thing but to have
someone else have issues as well, that's makes me wonder.  Is there
something funny going on that only affects certain hardware or something
like that?  How would one test it to see what is wrong when it is only a
couple or a few people? 

Dale

:-)  :-) 

Re: [gentoo-user] downgrading gcc

[Alan McKinnon]

On Monday 20 April 2009 09:30:56 Dale wrote:
> That said, it has worked well for me.  Everything on my rig is working
> again.  If he has to do this downgrade of gcc, then a emerge -e world
> and everything works again, I'm going to really wonder what the deal is
> with gcc.  Just me running into problems is one thing but to have
> someone else have issues as well, that's makes me wonder.  Is there
> something funny going on that only affects certain hardware or something
> like that?  How would one test it to see what is wrong when it is only a
> couple or a few people?

It's more likely a compatibility issue between very specific modules or bits 
of code that affect lots of systems. Take for example this elog from the 
nvidia drivers:

===
This ebuild installs a kernel module and X driver. Both must
match explicitly in their version. This means, if you restart
X, you most modprobe -r nvidia before starting it back up
===

The interfaces that these things use have never been guaranteed to be stable, 
and gcc itself is free (within reason) to lay things out in memory anyway it 
sees fit. You get the same thing with X and it's drivers too. It makes sense - 
a server and it's drivers should all be part of the same release series and be 
built together with the same toolchain for best results.

You DON'T get this problem with normal packages. You can upgrade and downgrade 
cairo all day long if you want and firefox won't care - the API it uses is 
stable and doesn't change.

In your case and Mark's, you tried to downgrade something critical but have no 
information about what you should be downgrading to. When you synced portage, 
you lost the information about what was the latest arch and ~arch versions. 
Upgrade is easy - "emerge latest <arch> for everything, we know it works", but 
portage doesn't offer a rollback function so downgrade is much harder. Once 
someone has figured out $LIST, you can "emerge $LIST" and life is good, but 
you don't have $LIST yet.

Logic tells me you had two problems, and gcc is neither of them. Your box does 
not like latest X for whatever reason (problem 1) but you can't rollback to 
the last working version of everything involved as you don't know what it is 
(problem 2).

So when all other efforts have failed, downgrade gcc and rebuild everything is 
very likely to fix those problems.

-- 
alan dot mckinnon at gmail dot com

Re: [gentoo-user] downgrading gcc

[Dale]

Alan McKinnon wrote:
>
> It's more likely a compatibility issue between very specific modules or bits 
> of code that affect lots of systems. Take for example this elog from the 
> nvidia drivers:
>
> ===
> This ebuild installs a kernel module and X driver. Both must
> match explicitly in their version. This means, if you restart
> X, you most modprobe -r nvidia before starting it back up
> ===
>
> The interfaces that these things use have never been guaranteed to be stable, 
> and gcc itself is free (within reason) to lay things out in memory anyway it 
> sees fit. You get the same thing with X and it's drivers too. It makes sense - 
> a server and it's drivers should all be part of the same release series and be 
> built together with the same toolchain for best results.
>
> You DON'T get this problem with normal packages. You can upgrade and downgrade 
> cairo all day long if you want and firefox won't care - the API it uses is 
> stable and doesn't change.
>
> In your case and Mark's, you tried to downgrade something critical but have no 
> information about what you should be downgrading to. When you synced portage, 
> you lost the information about what was the latest arch and ~arch versions. 
> Upgrade is easy - "emerge latest <arch> for everything, we know it works", but 
> portage doesn't offer a rollback function so downgrade is much harder. Once 
> someone has figured out $LIST, you can "emerge $LIST" and life is good, but 
> you don't have $LIST yet.
>
> Logic tells me you had two problems, and gcc is neither of them. Your box does 
> not like latest X for whatever reason (problem 1) but you can't rollback to 
> the last working version of everything involved as you don't know what it is 
> (problem 2).
>
> So when all other efforts have failed, downgrade gcc and rebuild everything is 
> very likely to fix those problems.
>
>   

While I'm not a dev, I do know this.  All I did was downgrade gcc and a
emerge -e world.  After that, things started working again.  X wasn't
crashing, Seamonkey wasn't crashing, my USB ports starting working
again, my sound started working again and several other little things
that were "weird".  So far, I haven't changed any config files or any
versions of a package.  I haven't syncd the tree on this machine
either.  I didn't want to complicate things any farther with portage
wanting to upgrade something else when I'm trying to get back to a
stable system, 

The thing to notice is this, nothing changed but gcc.  That's all.  It
is odd to me that when I upgraded gcc, things started to break.  When I
downgrade gcc, things start to work again.  Since nothing else changed,
in my mind, it has to be gcc.  I may be wrong but the fact it works is
undeniable.  I'm all for what works.

Dale

:-)  :-)

Re: [gentoo-user] downgrading gcc

[Mark Knecht]

On Mon, Apr 20, 2009 at 12:48 AM, Alan McKinnon <alan.mckinnon@gmail.com> wrote:
> On Monday 20 April 2009 09:30:56 Dale wrote:
>> That said, it has worked well for me.  Everything on my rig is working
>> again.  If he has to do this downgrade of gcc, then a emerge -e world
>> and everything works again, I'm going to really wonder what the deal is
>> with gcc.  Just me running into problems is one thing but to have
>> someone else have issues as well, that's makes me wonder.  Is there
>> something funny going on that only affects certain hardware or something
>> like that?  How would one test it to see what is wrong when it is only a
>> couple or a few people?
>
> It's more likely a compatibility issue between very specific modules or bits
> of code that affect lots of systems. Take for example this elog from the
> nvidia drivers:
>
> ===
> This ebuild installs a kernel module and X driver. Both must
> match explicitly in their version. This means, if you restart
> X, you most modprobe -r nvidia before starting it back up
> ===
>
> The interfaces that these things use have never been guaranteed to be stable,
> and gcc itself is free (within reason) to lay things out in memory anyway it
> sees fit. You get the same thing with X and it's drivers too. It makes sense -
> a server and it's drivers should all be part of the same release series and be
> built together with the same toolchain for best results.
>
> You DON'T get this problem with normal packages. You can upgrade and downgrade
> cairo all day long if you want and firefox won't care - the API it uses is
> stable and doesn't change.
>
> In your case and Mark's, you tried to downgrade something critical but have no
> information about what you should be downgrading to. When you synced portage,
> you lost the information about what was the latest arch and ~arch versions.
> Upgrade is easy - "emerge latest <arch> for everything, we know it works", but
> portage doesn't offer a rollback function so downgrade is much harder. Once
> someone has figured out $LIST, you can "emerge $LIST" and life is good, but
> you don't have $LIST yet.
>
> Logic tells me you had two problems, and gcc is neither of them. Your box does
> not like latest X for whatever reason (problem 1) but you can't rollback to
> the last working version of everything involved as you don't know what it is
> (problem 2).
>
> So when all other efforts have failed, downgrade gcc and rebuild everything is
> very likely to fix those problems.
>
> --
> alan dot mckinnon at gmail dot com
>
>

Alan,
   Hi. Thanks for your inputs and help. I appreciate it.

   I think you've covered most of the issues fairly clearly. What you
cannot cover is the specifics of my hardware, so I'll try to do this
based on what I think I've learned. As best I can tell the failure I'm
seeing is a segfault in the Intel VGA driver when doing xv video.
OpenGL works fine, and other than xv the Intel driver works fine for
me. Using mplayer I can watch videos when I choose OpenGL rendering.
All applications fail when using xv, but my initial realization came
from mythfrontend which is why this has had a 'mythtv segfaults' title
in the past. None the less it's really xv. There are 1 line segfault
messages in different log files after the crash pointing at the i915
driver saying it cannot pin an xv buffer in memory. This is apparently
known at X.org as I found and posted my results in an existing bug
report - one of many on apparently the same issue.

   Note that if you, or the person who decided to mark xorg-server-1.5
and gcc-4.3.2 stable didn't have Intel hardware, then only if they
actually ran xv video apps, they wouldn't have seen this problem. This
sort of problem is (to me) a root weakness of the Gentoo package
management system. Nothing is really 'stable' as it's not tested
against a wide range of known hardware platforms with a know set of
test cases before it's marked 'stable' so this sort of thing happens
now and again. There is no reason for you to say X isn't stable, or
gcc causes problems because everything works on your system. (Or you
think it does!) ;-)

   In my case I *think* the problem showed up only after rebuilding X
with gcc-4.3.2 but at this point I've unfortunately sort of lost track
of the whole history. I *believe* that gcc got upgraded, I switched my
compiler to the newer 4.3.2 version, then an X upgrade came along, got
built and started failing.

   My first attempt at fixing this was to downgrade xorg-server back
to 1.3. This failed, but it was built with the newer compiler so it
wasn't a real downgrade in the sense of going back to what I had
before. I then tried moving to xorg-x11-7.4 which some people at X.org
said fixed the problem for them. Unfortunately for me it didn't.

   Over the years this sort of thing has happened a few times with
Gentoo so maybe once every 2 years I'll do an emerge -e system, emerge
-e world just to make sure everything is up to date. As I was having
problems I decided to do that and move the whole machine to 4.3.2. I
got started with that process a couple of days ago.

   Around that time Michael was having trouble with his USB hardware
and the thread had similarities. His solution was to downgrade gcc.
However I had already started rebuilding my machine with the new
compiler so I couldn't really do that, nor did I want to because if it
was a mismatch between something compiled with 4.1.2 and 4.3.2 then it
should have been fixed with 4.3.2. Unfortunately moving the whole
machine to 4.3.2 didn't solve the problem. xv video still segfaults.

   This leaves me with a machine that's completely up-to-date but
unfortunately doesn't work the way it did for the last 3 years so as
an experiment I'm now moving the machine back to 4.1.2. This first
pass will get done tonight and maybe by tomorrow I'll know if X-7.4
and the newer Intel driver is functional with 4.1.2. If it is, great.
If not, then I suppose I'll try going back to X-7.2/xorg-server-1.3.
Don't know.

   Anyway, I don't think I added any value with this post. Just
documentation and possibly some clarity.

Cheers,
Mark

[gentoo-user] Downgrading gcc

[meino.cramer]

Hi,

I want to downgrade gcc from 4.5.3-r1 to 4.4.5.

The Gentoo gcc UPgrade guide tells me, that ABI are only upward
compatible which implies problems when downgrading and not upgrading.

Nonetheless a downgrade is needed here and I want to go 
to gcc-4.4.5.

How can I acchieve this in a clean way?

Best regards,
mcc

Re: [gentoo-user] Downgrading gcc

[Pandu Poluan]

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Just re-emerge the older version e.g. emerge =...gcc-4.4.5 (... is the
category). Then use eselect gcc or gcc-config to select the active gcc
version.

CMIIW

Rgds,
 On Feb 20, 2012 11:24 AM, <meino.cramer@gmx.de> wrote:

> Hi,
>
> I want to downgrade gcc from 4.5.3-r1 to 4.4.5.
>
> The Gentoo gcc UPgrade guide tells me, that ABI are only upward
> compatible which implies problems when downgrading and not upgrading.
>
> Nonetheless a downgrade is needed here and I want to go
> to gcc-4.4.5.
>
> How can I acchieve this in a clean way?
>
> Best regards,
> mcc
>
>
>
>
>
>
>
>

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