linux-kernel - Re: [PATCH] x86/signals: Fix save/restore signal stack to correctly support sigset

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Message-ID: <20201129032823.GA3579531@ZenIV.linux.org.uk>
Date:   Sun, 29 Nov 2020 03:28:23 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Walt Drummond <walt@...mmond.us>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, brgerst@...il.com, linux@...inikbrodowski.net,
        gustavoars@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/signals: Fix save/restore signal stack to correctly
 support sigset_t

On Sat, Nov 28, 2020 at 06:19:31PM -0800, Walt Drummond wrote:
> Thanks Al.  I want to understand the nuance, so please bear with me as I
> reason this out.   The cast in stone nature of this is due to both the need
> to keep userspace and kernel space in sync (ie, you'd have to coordinate
> libc and kernel changes super tightly to pull this off), and any change in
> the size of struct rt_sigframe would break backwards compatibility with
> older binaries, is that correct?

Pretty much so.  I would expect gdb and friends to be very unhappy about
that, for starters, along with a bunch of fun stuff like JVM, etc.

Ask the userland folks (libc, gdb, etc.) how would they feel about such
changes.  I'm fairly sure that it's _not_ going to be a matter of
changing _NSIG, rebuilding the kernel and living happily ever after.