From: Andy Lutomirski <luto@amacapital.net>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: "Ingo Molnar" <mingo@kernel.org>,
"Jan Beulich" <JBeulich@suse.com>,
"Borislav Petkov" <bp@alien8.de>,
"Peter Zijlstra" <a.p.zijlstra@chello.nl>,
"Ingo Molnar" <mingo@elte.hu>, "Brian Gerst" <brgerst@gmail.com>,
"Frédéric Weisbecker" <fweisbec@gmail.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Denys Vlasenko" <dvlasenk@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
"Frank Ch. Eigler" <fche@redhat.com>
Subject: Re: [PATCH] x86/debug: Remove perpetually broken, unmaintainable dwarf annotations
Date: Mon, 1 Jun 2015 12:53:36 -0700 [thread overview]
Message-ID: <CALCETrW5fQ_F_UoLBXbwN8z_+kLMpTiST-za_qdP-oBhaavqLQ@mail.gmail.com> (raw)
In-Reply-To: <20150601194516.GA6110@treble.redhat.com>
On Mon, Jun 1, 2015 at 12:45 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> On Fri, May 29, 2015 at 10:47:31AM -0700, Andy Lutomirski wrote:
>> On Thu, May 28, 2015 at 6:17 AM, Ingo Molnar <mingo@kernel.org> wrote:
>> >
>> > * Jan Beulich <JBeulich@suse.com> wrote:
>> >
>> >> > and meanwhile you can keep a revert of this patch ported to SUSE kernels in
>> >> > whatever fashion you prefer.
>> >>
>> >> Funny suggestion - I don't think that's reasonable for us to do. Or if we were
>> >> to, we could as well invest in doing the re-work you're asking for; I don't
>> >> think anyone will have the time to do either.
>> >
>> > That's fair enough: if there's not enough resources to keep a feature maintainable
>> > upstream then it should not be upstream in that form.
>> >
>> > This isn't just some driver we can let bit-rot in peace until it finds a
>> > maintainer (or not), without affecting anyone but users of that driver.
>> >
>> > This is hundreds of usage sites of ugly code intermixed with critical pieces of
>> > assembly code that negatively affects the hackability of everything.
>> >
>> > Also, with the feature missing completely, maybe someone finds a method to
>> > introduce it in a maintainable fashion, while with the feature included upstream
>> > there's very little pressure to do that. As a bonus we'd also win a workable dwarf
>> > unwinder.
>>
>> Before doing something drastic like this, I think we should get Josh's
>> opinion, since I think he's working on a new (?) unwinder.
>>
>> FWIW, musl is considering some kind of automatic annotation scheme:
>>
>> http://www.openwall.com/lists/musl/2015/05/13/5
>
> Thanks for the link! I found a newer version of it here:
>
> http://www.openwall.com/lists/musl/2015/05/31/5
>
> Overall I think that script is a really good solution.
>
> From what I can tell, it tracks the CFA (stack pointer) perfectly.
> (Which is actually pretty straightfoward if you just hook into function
> entry/exit, push/pop, and add/sub to rsp).
>
> It also does a nice job at making a best effort at tracking the caller's
> register values (which are less important than CFA but still nice to
> have).
It might be nice to be able to reliably unwind out from an exception /
interrupt / syscall frame into userspace or into the kernel code that
trapped, complete with registers.
In any event, we'll almost certainly have to manually annotate these
weird types of entries. I wonder if we could manage to annotate just
the entry parts and let a magic script do the rest.
--Andy
next prev parent reply other threads:[~2015-06-01 19:54 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-28 8:20 [PATCH] x86-64: fix unwind info for incomplete frames Jan Beulich
2015-05-28 9:01 ` Ingo Molnar
2015-05-28 9:45 ` Jan Beulich
2015-05-28 11:20 ` [PATCH] x86/debug: Remove perpetually broken, unmaintainable dwarf annotations Ingo Molnar
2015-05-28 11:39 ` [PATCH v2] " Ingo Molnar
2015-05-28 11:51 ` [PATCH] " Jan Beulich
2015-05-28 13:17 ` Ingo Molnar
2015-05-29 17:47 ` Andy Lutomirski
2015-05-29 20:27 ` Josh Poimboeuf
2015-05-29 21:39 ` Frank Ch. Eigler
2015-06-01 19:45 ` Josh Poimboeuf
2015-06-01 19:53 ` Andy Lutomirski [this message]
2015-06-01 20:19 ` Josh Poimboeuf
2015-06-02 5:57 ` Ingo Molnar
2015-06-02 14:46 ` Josh Poimboeuf
2015-06-02 17:00 ` Andy Lutomirski
2015-06-05 17:11 ` Andi Kleen
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