getcontext returns ENOSYS

[Richard W.M. Jones]

Has anyone tried to port software which uses getcontext/setcontext
(ie. coroutines, green threads etc)?

Although we have compiled qemu for ARM, it fails to run because
getcontext returns an error with errno == ENOSYS.  qemu contains its
own coroutine implementation.

Rich.

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[Richard W.M. Jones]

On Fri, Apr 27, 2012 at 07:58:38PM +0100, Richard W.M. Jones wrote:
>  
>  Has anyone tried to port software which uses getcontext/setcontext
>  (ie. coroutines, green threads etc)?
>  
>  Although we have compiled qemu for ARM, it fails to run because
>  getcontext returns an error with errno == ENOSYS.  qemu contains its
>  own coroutine implementation. 
OK looking at this a bit more, it turns out that Linaro hit this bug a
month or two ago and added a *context implementation in glibc-ports:

https://bugs.launchpad.net/qemu-linaro/+bug/883136
http://sourceware.org/ml/libc-ports/2012-02/msg00077.html
Upstream:
http://sourceware.org/git/?p=glibc-ports.git;a=commit;h=402a76b62dded0ee9...

I'm a bit confused about the relationship of glibc, glibc-ports,
Fedora and ARM.  Can we include this patch in our glibc package to fix
the bug in our qemu?

I'd prefer a real implementation of the ucontext functions, instead of
using the much less tested threads fallback code in qemu.

Rich.

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[Richard W.M. Jones]

For the record, attached is the patch to Fedora glibc.  It works, and
gets us past the missing ucontext problem.

However, qemu-system-arm fails very quickly afterwards somewhere in
TCG code.  I suspect that qemu cannot emulate the same hardware as
required by my kernel (vmlinuz-3.3.2-8.fc17.armv7hl.tegra), although
there is not much to go on.

Anyone have a primer on all the different ARM architectures?

Rich.

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[Peter Robinson]

On Sat, Apr 28, 2012 at 2:39 PM, Richard W.M. Jones <rjones(a)redhat.com&gt; wrote:
>  For the record, attached is the patch to Fedora glibc.  It works, and
>  gets us past the missing ucontext problem. 
If we need this eventually for qemu on ARM can you file a bug against
glibc and attach the patch there so the glibc maintainer can review
and add it as necessary.

Peter

[Richard W.M. Jones]

On Sat, Apr 28, 2012 at 03:29:54PM +0100, Peter Robinson wrote:
>  On Sat, Apr 28, 2012 at 2:39 PM, Richard W.M. Jones
> <rjones(a)redhat.com&gt; wrote:
>  >
>  > For the record, attached is the patch to Fedora glibc.  It works, and
>  > gets us past the missing ucontext problem.
>  
>  If we need this eventually for qemu on ARM can you file a bug against
>  glibc and attach the patch there so the glibc maintainer can review
>  and add it as necessary. 
Sure:
https://bugzilla.redhat.com/show_bug.cgi?id=817276

Rich.

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[Peter Robinson]

On Sat, Apr 28, 2012 at 3:38 PM, Richard W.M. Jones <rjones(a)redhat.com&gt; wrote:
>  On Sat, Apr 28, 2012 at 03:29:54PM +0100, Peter Robinson wrote:
> > On Sat, Apr 28, 2012 at 2:39 PM, Richard W.M. Jones <rjones(a)redhat.com&gt; wrote:
> > >
> > > For the record, attached is the patch to Fedora glibc.  It works, and
> > > gets us past the missing ucontext problem.
> >
> > If we need this eventually for qemu on ARM can you file a bug against
> > glibc and attach the patch there so the glibc maintainer can review
> > and add it as necessary.
>
>  Sure:
>  https://bugzilla.redhat.com/show_bug.cgi?id=817276 
Thanks,
Pete

[Michael Hope]

On 29 April 2012 01:39, Richard W.M. Jones <rjones(a)redhat.com&gt; wrote:
>  For the record, attached is the patch to Fedora glibc.  It works, and
>  gets us past the missing ucontext problem.
>
>  However, qemu-system-arm fails very quickly afterwards somewhere in
>  TCG code.  I suspect that qemu cannot emulate the same hardware as
>  required by my kernel (vmlinuz-3.3.2-8.fc17.armv7hl.tegra), although
>  there is not much to go on.
>
>  Anyone have a primer on all the different ARM architectures? 
Hi Richard.  I recommend the Versatile Express A9 model.  It's one of
our supported platforms, has good kernel support in Linus's tree, and
has a decent amount of memory.  It's the seed system model for the KVM
work we're looking at.

There's more information at:
 https://wiki.linaro.org/PeterMaydell/QemuVersatileExpress

and my quick start at:
 https://wiki.linaro.org/MichaelHope/Sandbox/QEMUCrossTest

You'd probably want a Fedora kernel and libvirt instance instead of our tools.

-- Michael