linux-kernel - Re: [PATCH v2 1/4] x86/signal/64: Add a comment about sigcontext->fs and gs

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Message-ID: <5634DD68.4090709@list.ru>
Date:	Sat, 31 Oct 2015 18:25:28 +0300
From:	Stas Sergeev <stsp@...t.ru>
To:	Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Cc:	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v2 1/4] x86/signal/64: Add a comment about sigcontext->fs
 and gs

26.10.2015 04:25, Andy Lutomirski пишет:
> These fields have a strange history.  This tries to document it.
>
> This borrows from 9a036b93a344 ("x86/signal/64: Remove 'fs' and 'gs'
> from sigcontext"), which was reverted by ed596cde9425 ("Revert x86
> sigcontext cleanups").
>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
Now the strategy about SS is to always save it to the sigcontext.
This is good because the syscall can clobber it, so the app had
to be very careful in the past trying to save it by hands.
How about saving also fs and gs? (without restoring yet)
If you do, you'll save dosemu a headache of doing any "pre-syscall"
work. Pre-syscall work is very nasty.
I haven't checked if the syscall clobber also these or only SS,
but perhaps saving them by the kernel won't hurt?
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