Does anyone care about gcc 3.x support for x86 anymore?

Does anyone care about gcc 3.x support for x86 anymore?

[H. Peter Anvin]

Recently, we have seen an increasing number of problems with gcc 3.4 on
x86; mostly due to poor constant propagation producing not just bad code
but failing to properly eliminate what should be dead code.

I'm wondering if there is any remaining real use of gcc 3.4 on x86 for
compiling current kernels (as opposed to residual use for compiling
applications on old enterprise distros.)  I'm specifically not referring
to other architectures here -- most of these issues have been in
relation to low-level arch-specific code, and as such only affects the
x86 architectures.  Other architectures may very well have a much
stronger need for continued support of an older toolchain.

If there isn't a reason to preserve support, I would like to consider
discontinue support for using gcc 3 to compile x86 kernels.  If there is
a valid use case, it would be good to know what it is.

	-hpa

Does anyone care about gcc 3.x support for *x86* anymore?

[H. Peter Anvin]

[Reposting as a separate thread]

Recently, we have seen an increasing number of problems with gcc 3.4 on
x86; mostly due to poor constant propagation producing not just bad code
but failing to properly eliminate what should be dead code.

I'm wondering if there is any remaining real use of gcc 3.4 on x86 for
compiling current kernels (as opposed to residual use for compiling
applications on old enterprise distros.)  I'm specifically not referring
to other architectures here -- most of these issues have been in
relation to low-level arch-specific code, and as such only affects the
x86 architectures.  Other architectures may very well have a much
stronger need for continued support of an older toolchain.

If there isn't a reason to preserve support, I would like to consider
discontinue support for using gcc 3 to compile x86 kernels.  If there is
a valid use case, it would be good to know what it is.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: Does anyone care about gcc 3.x support for *x86* anymore?

[Ingo Molnar]

(reposted with Andrew and Linus Cc:-ed too)

* H. Peter Anvin <hpa@zytor.com> wrote:

> [Reposting as a separate thread]
> 
> Recently, we have seen an increasing number of problems 
> with gcc 3.4 on x86; mostly due to poor constant 
> propagation producing not just bad code but failing to 
> properly eliminate what should be dead code.
> 
> I'm wondering if there is any remaining real use of gcc 
> 3.4 on x86 for compiling current kernels (as opposed to 
> residual use for compiling applications on old 
> enterprise distros.)  I'm specifically not referring to 
> other architectures here -- most of these issues have 
> been in relation to low-level arch-specific code, and as 
> such only affects the x86 architectures.  Other 
> architectures may very well have a much stronger need 
> for continued support of an older toolchain.
> 
> If there isn't a reason to preserve support, I would 
> like to consider discontinue support for using gcc 3 to 
> compile x86 kernels.  If there is a valid use case, it 
> would be good to know what it is.
> 
> 	-hpa
> 
> -- 
> H. Peter Anvin, Intel Open Source Technology Center
> I work for Intel.  I don't speak on their behalf.

Re: Does anyone care about gcc 3.x support for *x86* anymore?

[Andi Kleen]

"H. Peter Anvin" <hpa@zytor.com> writes:
>
> If there isn't a reason to preserve support, I would like to consider
> discontinue support for using gcc 3 to compile x86 kernels.  If there is
> a valid use case, it would be good to know what it is.

I suspect there are still distributions around that use it as a standard
compiler. Wasn't it used in some major release of Debian?

-Andi
-- 
ak@linux.intel.com -- Speaking for myself only.

Re: Does anyone care about gcc 3.x support for *x86* anymore?

[H. Peter Anvin]

On 05/19/2010 06:38 AM, Andi Kleen wrote:
> "H. Peter Anvin" <hpa@zytor.com> writes:
>>
>> If there isn't a reason to preserve support, I would like to consider
>> discontinue support for using gcc 3 to compile x86 kernels.  If there is
>> a valid use case, it would be good to know what it is.
> 
> I suspect there are still distributions around that use it as a standard
> compiler. Wasn't it used in some major release of Debian?
> 
> -Andi

There are, but that doesn't mean it's relevant for people to compile
bleeding-edge kernels with it.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

Re: Does anyone care about gcc 3.x support for *x86* anymore?

[Justin P. Mattock]

On 05/19/2010 07:08 AM, H. Peter Anvin wrote:
> On 05/19/2010 06:38 AM, Andi Kleen wrote:
>> "H. Peter Anvin"<hpa@zytor.com>  writes:
>>>
>>> If there isn't a reason to preserve support, I would like to consider
>>> discontinue support for using gcc 3 to compile x86 kernels.  If there is
>>> a valid use case, it would be good to know what it is.
>>
>> I suspect there are still distributions around that use it as a standard
>> compiler. Wasn't it used in some major release of Debian?
>>
>> -Andi
>
> There are, but that doesn't mean it's relevant for people to compile
> bleeding-edge kernels with it.
>
> 	-hpa
>

no need for it here(using 4.6.0)..
Any distro still using this version
should upgrade(but who am I to say anything)

cheers.

Justin P. Mattock

Re: Does anyone care about gcc 3.x support for x86 anymore?

[Mauro Carvalho Chehab]

H. Peter Anvin wrote:
> Recently, we have seen an increasing number of problems with gcc 3.4 on
> x86; mostly due to poor constant propagation producing not just bad code
> but failing to properly eliminate what should be dead code.

I don't see any problem, as, if people are using gcc3, they are probably
not interested on the bleeding edge kernel. 

However, if the problems are just performance/dead code removal, I would 
just add a big warning if someone tries to compile x86 with it. I don't 
like very much the idea of having different minimum gcc requirements 
for each architecture, except if gcc is producing a broken code. 

Currently,Documentation/Changes list just a common minimal list for
everything - although the text describing gcc say that the "version 
requirements" may vary for each CPU type.

-- 

Cheers,
Mauro

Re: Does anyone care about gcc 3.x support for x86 anymore?

[H. Peter Anvin]

On 05/19/2010 04:10 PM, Mauro Carvalho Chehab wrote:
> H. Peter Anvin wrote:
>> Recently, we have seen an increasing number of problems with gcc 3.4 on
>> x86; mostly due to poor constant propagation producing not just bad code
>> but failing to properly eliminate what should be dead code.
> 
> I don't see any problem, as, if people are using gcc3, they are probably
> not interested on the bleeding edge kernel. 
> 
> However, if the problems are just performance/dead code removal, I would 
> just add a big warning if someone tries to compile x86 with it. I don't 
> like very much the idea of having different minimum gcc requirements 
> for each architecture, except if gcc is producing a broken code. 
> 
> Currently,Documentation/Changes list just a common minimal list for
> everything - although the text describing gcc say that the "version 
> requirements" may vary for each CPU type.
> 

We already have different gcc version requirements, whether or not
they're written down is another matter...

	-hpa

Re: Does anyone care about gcc 3.x support for x86 anymore?

[H. Peter Anvin]

On 05/19/2010 04:10 PM, Mauro Carvalho Chehab wrote:
> 
> However, if the problems are just performance/dead code removal, I would 
> just add a big warning if someone tries to compile x86 with it. I don't 
> like very much the idea of having different minimum gcc requirements 
> for each architecture, except if gcc is producing a broken code. 
> 

I should clarify the problem.  The problems we have seen are related to
constant propagation, which causes gcc3 to die when there is an assembly
constraint like:

	asm("..." : : "i" (foo));

... since "foo" isn't constant as far as it is concerned.  We can put in
workarounds, but it's real effort to keep it alive that probably isn't
well spent.

Similarly, lack of constant propagation can cause code that should have
been compile-time removed to still be there, causing link failures.

	-hpa

Re: Does anyone care about gcc 3.x support for x86 anymore?

[Ingo Molnar]

* H. Peter Anvin <hpa@zytor.com> wrote:

> On 05/19/2010 04:10 PM, Mauro Carvalho Chehab wrote:
> > 
> > However, if the problems are just performance/dead 
> > code removal, I would just add a big warning if 
> > someone tries to compile x86 with it. I don't like 
> > very much the idea of having different minimum gcc 
> > requirements for each architecture, except if gcc is 
> > producing a broken code.
> > 
> 
> I should clarify the problem.  The problems we have seen 
> are related to constant propagation, which causes gcc3 
> to die when there is an assembly constraint like:
> 
> 	asm("..." : : "i" (foo));
> 
> ... since "foo" isn't constant as far as it is 
> concerned.  We can put in workarounds, but it's real 
> effort to keep it alive that probably isn't well spent.
> 
> Similarly, lack of constant propagation can cause code 
> that should have been compile-time removed to still be 
> there, causing link failures.

Put in a deprecation warning first perhaps?

	Ingo

Re: Does anyone care about gcc 3.x support for *x86* anymore?

[Martin Michlmayr]

* Andi Kleen <andi@firstfloor.org> [2010-05-19 15:38]:
> > If there isn't a reason to preserve support, I would like to consider
> > discontinue support for using gcc 3 to compile x86 kernels.  If there is
> > a valid use case, it would be good to know what it is.
> 
> I suspect there are still distributions around that use it as a standard
> compiler. Wasn't it used in some major release of Debian?

Not in a recent one, no.
-- 
Martin Michlmayr
http://www.cyrius.com/

Re: Does anyone care about gcc 3.x support for *x86* anymore?

[Miguel Ojeda]

On Thu, May 20, 2010 at 8:37 PM, Martin Michlmayr <tbm@cyrius.com> wrote:
> * Andi Kleen <andi@firstfloor.org> [2010-05-19 15:38]:
>> > If there isn't a reason to preserve support, I would like to consider
>> > discontinue support for using gcc 3 to compile x86 kernels.  If there is
>> > a valid use case, it would be good to know what it is.
>>
>> I suspect there are still distributions around that use it as a standard
>> compiler. Wasn't it used in some major release of Debian?
>
> Not in a recent one, no.

Not even in oldstable (etch).

> --
> Martin Michlmayr
> http://www.cyrius.com/
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
>