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Date: Mon, 12 Jan 2015 12:22:10 -0800
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andy Lutomirski <luto@amacapital.net>, Borislav Petkov <bp@alien8.de>
CC: Denys Vlasenko <dvlasenk@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, X86 ML <x86@kernel.org>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH] x86: introduce push/pop macros which generate CFI_REL_OFFSET
 and CFI_RESTORE
References: <1421017655-25561-1-git-send-email-dvlasenk@redhat.com> <20150112192314.GF3904@pd.tnic> <CALCETrXzEPKPFKBeKF3UMduNe1ViQTC6vULEySo_0XTJcK7Qkw@mail.gmail.com> <20150112193704.GG3904@pd.tnic> <CALCETrUVXGnqqtgw1eZRK5g0B+5vwGuvSV6dwnm5witA-fJWLQ@mail.gmail.com> <20150112201145.GH3904@pd.tnic> <CALCETrVto_uxTz30M8a4XyLk-UXTQXc3CsYxEKJkhmqH=FdvNA@mail.gmail.com>
In-Reply-To: <CALCETrVto_uxTz30M8a4XyLk-UXTQXc3CsYxEKJkhmqH=FdvNA@mail.gmail.com>
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On 01/12/2015 12:14 PM, Andy Lutomirski wrote:
> On Mon, Jan 12, 2015 at 12:11 PM, Borislav Petkov <bp@alien8.de> wrote:
>> On Mon, Jan 12, 2015 at 11:46:53AM -0800, Andy Lutomirski wrote:
>>> Dumb example:
>>>
>>>     pushq_cfi $__KERNEL_DS /* ss */
>>>
>>> This doesn't save anything that the unwinder would care about.
>>
>> And? The unwinder or whatever looks at that info simply ignores stuff it
>> is not interested in, no?
> 
> But CFI_REL_OFFSET $__KERNEL_DS, 0 probably isn't even well-formed and
> won't build.
> 

I think this is relatively easy to deal with at the expense of a large
.ifeq statement in the macro.

	-hpa