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

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Message-ID: <CALCETrU1uNY=1tFudouZGQuVkBzR6gvxUV6-3Yeu_OE8dG9e-Q@mail.gmail.com>
Date:	Tue, 29 Dec 2015 04:31:42 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Stas Sergeev <stsp@...t.ru>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Brian Gerst <brgerst@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 1/4] x86/signal/64: Add a comment about sigcontext->fs
 and gs

On Tue, Dec 29, 2015 at 4:24 AM, Stas Sergeev <stsp@...t.ru> wrote:
> 08.12.2015 02:23, Andy Lutomirski пишет:
>> On Oct 31, 2015 8:25 AM, "Stas Sergeev" <stsp@...t.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@...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?
>>
>> There's a bunch of ongoing work about FS and GS.  I want to wait and see.
> Andy, have you postponed only this, or also the sigreturn patch?
> Long time no news...
> sigreturn patch would really be nice to have.

Sorry, I got caught up with a bunch of other stuff, and everyone being
slow with the holiday season.  There's some slight chance we'll get it
in for 4.5, but 4.6 is more likely.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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