[Buildroot] [PATCH] jack2: Try better fix for NGREG problem

[Alexey Brodkin]

Hi Thomas,

On Mon, 2016-11-21 at 15:54 +0100, Thomas Petazzoni wrote:
> Hello,
> 
> On Mon, 21 Nov 2016 17:49:55 +0300, Alexey Brodkin wrote:
> > 
> > After quite some time trying this and that we seem to have no
> > better solution than proposed by Thomas back in the day [1].
> > 
> > The solution in question is to check [during jack2 configuration]
> > if NGREG is exposed via ucontext.h and then use its value in
> > source code later on. This replaces long and still growing list
> > of architectures for which we explicitly escape usage of NGREG.
> > 
> > Just for reference [2] is my attempt to fix in in the other
> > supposedly better way but with no luck because of the mess in
> > kernel's UAPI headers.
> > 
> > [1] http://lists.busybox.net/pipermail/buildroot/2016-May/161785.html
> > [2] http://lists.busybox.net/pipermail/buildroot/2016-June/162461.html
> > 
> > Still not sure if that works for every other architectures, so testing
> > and Acks from all interested parties are much appreciated.
> 
> Unfortunately, I experimented with something like this some time ago,
> and IIRC, it didn't work all architectures, because NGREG is not always
> defined in <ucontext.h>, but can be defined in other header files (if I
> recall). In the end, I think I ended up with something like the below,
> but I don't remember if I tested it in all cases:
> 
> (As you can see, it dates back from May 2016...)
> 
> From 15685fd4409486e7059bb480193d1086c5634910 Mon Sep 17 00:00:00 2001
> From: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
> Date: Mon, 23 May 2016 22:28:12 +0200
> Subject: [PATCH] Improve check for ucontext
> 
> The ucontext functionality is not available on all CPUs with all C
> libraries. Instead of making just assumptions based on the CPU
> architecture, this commit adds the necessary checks in wscript to verify
> the availability of the ucontext functionality, before using it in
> dbus/sigsegv.c.
> 
> This avoids the long list of architecture exclusions, and make it more
> robust when building jack2 for new CPU architectures.
> 
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
> ---
>  dbus/sigsegv.c | 12 ++++++------
>  wscript        | 11 ++++++++++-
>  2 files changed, 16 insertions(+), 7 deletions(-)

That now looks really scary.
Maybe we follow much cleaner path and will remove that damned check where
NGREG is used all together? Anyways it was used let's say "not always" so
that might be not that bad solution.

What do you think?

Not sure if that corner case really requires more time from us.

-Alexey