Re: systemd on hppa and number of free RT signals

[Helge Deller <deller@gmx.de>]

Hi Carlos,

On 10/07/2014 11:03 PM, Carlos O'Donell wrote:
> On Tue, Oct 7, 2014 at 3:39 PM, Helge Deller <deller@gmx.de> wrote:
>> I've just had a successful boot on hppa with systemd :-)
>> The bootlog is attached.
>
> Awesome.

Thanks!
  
>> The attached patches to Linux kernel and glibc shuffles around some signals,
>> so that we end up with
>> #define __SIGRTMIN      32
>> instead of
>> #define __SIGRTMIN      37
>
> This is the right way to go.
>
> Yes it's an ABI event, but these are fundamentally niche architectures
> for which we can't ask everyone else to adjust.

Yes, that was my opinion too.
  
>> I do know that this changes the ABI and introduces a binary incompatibly.
>> Nevertheless, my testing with the new kernel and glibc didn't showed any
>> obvious problems, which means that I could install either of those and the
>> system didn't showed problems even after reboots.
>
> That's because the signals you moved/removed aren't used by anything :-)
>
>> Additionally, given the fact that we have very little users and live in
>> debian/gentoo unstable would IMHO justify such an incompatible change. Even
>> HP-UX support was dropped a few months back...
>> And we could easily rebuild packages like strace, gdb and such...
>
> That's right.
>
>> The other option would be to increase NSIG in kernel from 64 to 128 or
>> higher.
>
> No, that's a very very bad idea because it has consequences on
> sigset_t and that would really really immediately break userspace.
>
>> I did tried to come up with kernel patches for this now for a few weeks, but
>> ended up with the recognition, that this would require to duplicate nearly
>> all of Linux kernel signal handling and which would most likely introduce
>> new bugs.
>
> Agreed.
>
>> What's your opinion on this?
>
> Flawless hack. Very well reorganized. Your removal of SIGLOST, and
> reorganizing is the best I could come up with also.
>
> The only thing I will do different is make SIGEMT equal to SIGABRT,
> that way we preserve the semantics of what this operation means. Linux
> doesn't use SIGEMT, but it keeps hppa defining this for use by other
> software that might want similar semantics. You can catch SIGABRT and
> operate on it, so it's one way forward.

Good idea!
  
> If you agree I'll checkin to glibc master.

I think we should check in the kernel changes first, which I can cover.
That shouldn't be a problem, but I assume people (Linus?) may ask why we do this.
Does it makes sense to set up a Wiki page with some more info about it?
If yes, I think I might need some help there...

Helge