Kernel compiler

Kernel compiler

[Ralf Baechle]

Due to compiler bugs with named initializers the use of egcs 1.1.2 has
ben deprecated for Linux; Linux 2.4.0-test10 will refuse to compile with
older compilers.

mips64 users can ignore this message;  they're currently all using egcs 1.1.2
and therefore not affected.

  Ralf

Re: Kernel compiler

[Keith Owens]

On Fri, 3 Nov 2000 22:19:26 +0100, 
Ralf Baechle <ralf@oss.sgi.com> wrote:
>Due to compiler bugs with named initializers the use of egcs 1.1.2 has
>ben deprecated for Linux; Linux 2.4.0-test10 will refuse to compile with
>older compilers.

Correction.  gcc 2.7 has been deprecated, the recommended version is
gcc 2.91.66 (also known as egcs 1.1.2) or better.  Unfortunately RedHat
created an unofficial 2.96 which is known to miscompile the kernel, so
you cannot just use the "latest" gcc.  It is believed that gcc versions
2.91.66 through 2.95 inclusive are safe, as long as you use
-fno-strict-aliasing.

Re: Kernel compiler

[Ralf Baechle]

On Sat, Nov 04, 2000 at 01:44:22PM +1100, Keith Owens wrote:

> On Fri, 3 Nov 2000 22:19:26 +0100, 
> Ralf Baechle <ralf@oss.sgi.com> wrote:
> >Due to compiler bugs with named initializers the use of egcs 1.1.2 has
> >ben deprecated for Linux; Linux 2.4.0-test10 will refuse to compile with
> >older compilers.
> 
> Correction.  gcc 2.7 has been deprecated, the recommended version is
> gcc 2.91.66 (also known as egcs 1.1.2) or better.  Unfortunately RedHat
> created an unofficial 2.96 which is known to miscompile the kernel, so
> you cannot just use the "latest" gcc.  It is believed that gcc versions
> 2.91.66 through 2.95 inclusive are safe, as long as you use
> -fno-strict-aliasing.

Sigh, yes you're right as other have already pointed out on IRC ...

Gcc 2.7 is no longer being used for Linux/MIPS since a long time and I'd
simply bitbucket any bugreport related to it.  Most people are using egcs
1.0.3a for everything which is older than the required minimum version 1.1.2,
so we're in some trouble.

I've got reports regarding the 1.1.2 crosscompiler which say that it
misscompiles MIPS kernels, sigh ...

The reports regarding egcs 2.96 and newer misscompiling the kernel only
affect x86 or are other architecture affected as well?  I don't have any
pending compiler >= 2.96 related bug reports.

  Ralf

Re: Kernel compiler

[Keith M Wesolowski]

On Sat, Nov 04, 2000 at 03:53:26AM +0100, Ralf Baechle wrote:

> The reports regarding egcs 2.96 and newer misscompiling the kernel only
> affect x86 or are other architecture affected as well?  I don't have any
> pending compiler >= 2.96 related bug reports.

Somewhere between 1019 and 1023, a bug was introduced which causes
miscompilation. Symptom is oops on boot during RPC port lookups. I
don't know if this is still present, nor the exact nature of the
bug. It appears that some address offsets changed in the compiled code
from gcc 1019 to gcc 1023.

-- 
Keith M Wesolowski			wesolows@chem.unr.edu
University of Nevada			http://www.chem.unr.edu
Chemistry Department Systems and Network Administrator

Re: Kernel compiler

[Pete Popov]

>>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<<

On 11/3/00, 6:53:26 PM, Ralf Baechle <ralf@oss.sgi.com> wrote regarding Re: 
Kernel compiler:


> On Sat, Nov 04, 2000 at 01:44:22PM +1100, Keith Owens wrote:

> > On Fri, 3 Nov 2000 22:19:26 +0100,
> > Ralf Baechle <ralf@oss.sgi.com> wrote:
> > >Due to compiler bugs with named initializers the use of egcs 1.1.2 has
> > >ben deprecated for Linux; Linux 2.4.0-test10 will refuse to compile with
> > >older compilers.
> >
> > Correction.  gcc 2.7 has been deprecated, the recommended version is
> > gcc 2.91.66 (also known as egcs 1.1.2) or better.  Unfortunately RedHat
> > created an unofficial 2.96 which is known to miscompile the kernel, so
> > you cannot just use the "latest" gcc.  It is believed that gcc versions
> > 2.91.66 through 2.95 inclusive are safe, as long as you use
> > -fno-strict-aliasing.

> Sigh, yes you're right as other have already pointed out on IRC ...

> Gcc 2.7 is no longer being used for Linux/MIPS since a long time and I'd
> simply bitbucket any bugreport related to it.  Most people are using egcs
> 1.0.3a for everything which is older than the required minimum version 
1.1.2,
> so we're in some trouble.

> I've got reports regarding the 1.1.2 crosscompiler which say that it
> misscompiles MIPS kernels, sigh ...

What are the symptoms of a "miscompiled" kernel and how does one detect 
that (assuming that the kernel actually compiles successfully, but has 
problems running).

Pete

Re: Kernel compiler

[Keith Owens]

On Sat, 4 Nov 2000 03:53:26 +0100, 
Ralf Baechle <ralf@oss.sgi.com> wrote:
>The reports regarding egcs 2.96 and newer misscompiling the kernel only
>affect x86 or are other architecture affected as well?  I don't have any
>pending compiler >= 2.96 related bug reports.

At a guess (and it is only a guess), the problems will affect all
architectures.  AFAICT they are in the common optimization phase, the
kernel uses constructs that were undefined or poorly defined but worked
in gcc 2.95, 2.96 handles them differently.

Re: Kernel compiler

[Ralf Baechle]

On Sat, Nov 04, 2000 at 03:10:50AM +0000, Pete Popov wrote:

> > Sigh, yes you're right as other have already pointed out on IRC ...
> 
> > Gcc 2.7 is no longer being used for Linux/MIPS since a long time and I'd
> > simply bitbucket any bugreport related to it.  Most people are using egcs
> > 1.0.3a for everything which is older than the required minimum version 
> 1.1.2,
> > so we're in some trouble.
> 
> > I've got reports regarding the 1.1.2 crosscompiler which say that it
> > misscompiles MIPS kernels, sigh ...
> 
> What are the symptoms of a "miscompiled" kernel and how does one detect 
> that (assuming that the kernel actually compiles successfully, but has 
> problems running).

When trying to work on a serial terminal hooked up to an Indy it'll oops.

Question is if the compiler is buggy or if it's particular code generation
is just triggering a bug in the kernel code.

  Ralf

Re: Kernel compiler

[Alan Cox]

> The reports regarding egcs 2.96 and newer misscompiling the kernel only
> affect x86 or are other architecture affected as well?  I don't have any
> pending compiler >= 2.96 related bug reports.

The Red Hat 2.96 seems to compile 2.2 correctly when you fix the 2.2 bugs but
does miscompile x86 fs/buffers.c on 2.4 according to reports. I think with mips
you'd have to experiment. Also AFAIK that tree branch hasn't been tested on
mips 

Re: Kernel compiler

[Alan Cox]

> The reports regarding egcs 2.96 and newer misscompiling the kernel only
> affect x86 or are other architecture affected as well?  I don't have any
> pending compiler >= 2.96 related bug reports.

The Red Hat 2.96 seems to compile 2.2 correctly when you fix the 2.2 bugs but
does miscompile x86 fs/buffers.c on 2.4 according to reports. I think with mips
you'd have to experiment. Also AFAIK that tree branch hasn't been tested on
mips 

Re: Kernel compiler

[Ralf Baechle]

On Sat, Nov 04, 2000 at 10:40:42AM +0000, Alan Cox wrote:

> > The reports regarding egcs 2.96 and newer misscompiling the kernel only
> > affect x86 or are other architecture affected as well?  I don't have any
> > pending compiler >= 2.96 related bug reports.
> 
> The Red Hat 2.96 seems to compile 2.2 correctly when you fix the 2.2 bugs but
> does miscompile x86 fs/buffers.c on 2.4 according to reports. I think with mips
> you'd have to experiment. Also AFAIK that tree branch hasn't been tested on
> mips 

I asked Cort about their PPC experience and they also got trouble.  Reason
enough to ignore gcc-current for kernel use for now.  It's doing well
for userland however so we'll also have to use two compilers from now on,
one for kernel and one for userland.

Btw, I've now placed srpm and i386-linux rpms of a new release of the
egcs-1.1.2 Linux/MIPS crosscompiler on oss.sgi.com.  Users of the 64-bit
kernel, read Origin users should also update as this release has several
fixes.

  Ralf