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

From: Andy Lutomirski <luto@amacapital.net>
To: Stas Sergeev <stsp@list.ru>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
	Borislav Petkov <bp@alien8.de>, Brian Gerst <brgerst@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	X86 ML <x86@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH v2 1/4] x86/signal/64: Add a comment about sigcontext->fs and gs
Date: Mon, 7 Dec 2015 15:23:01 -0800	[thread overview]
Message-ID: <CALCETrXnMMad8zr7vRHhwcuqNQa9OEBUrgeGS1D6FXo0v+Whvw@mail.gmail.com> (raw)
In-Reply-To: <5634DD68.4090709@list.ru>

On Oct 31, 2015 8:25 AM, "Stas Sergeev" <stsp@list.ru> wrote:
>
> 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@kernel.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?

There's a bunch of ongoing work about FS and GS.  I want to wait and see.