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Date: Fri, 22 Jan 2016 08:36:38 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        live-patching@vger.kernel.org, Michal Marek <mmarek@suse.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andi Kleen <andi@firstfloor.org>, Pedro Alves <palves@redhat.com>,
        Namhyung Kim <namhyung@gmail.com>,
        Bernd Petrovitsch <bernd@petrovitsch.priv.at>,
        Chris J Arges <chris.j.arges@canonical.com>,
        Andrew Morton <akpm@linux-foundation.org>, Jiri Slaby <jslaby@suse.cz>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>, netdev@vger.kernel.org,
        daniel@iogearbox.net
Subject: Re: [PATCH 23/33] x86/asm/bpf: Create stack frames in bpf_jit.S
Message-ID: <20160122073638.GA28042@gmail.com>
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* Alexei Starovoitov <alexei.starovoitov@gmail.com> wrote:

> > > I could be missing something. I think either this patch is not need or you 
> > > need to teach the tool to ignore all JITed stuff. I don't think it's 
> > > practical to annotate everything. Different JITs do their own magic. s390 
> > > JIT is even more fancy.
> > 
> > Well, but the point of these patches isn't to make the tool happy.  It's 
> > really to make sure that runtime stack traces can be made reliable. Maybe I'm 
> > missing something but I don't see why JIT code can't honor 
> > CONFIG_FRAME_POINTER just like any other code.
> 
> It can if there is no performance cost added. I can speak for x64 JIT, but the 
> rest needs to be analyzed as well. My point was that may be it's easier to 
> ignore all JITed code and just say that such call stacks may be unreliable? 
> live-patching is not applicable to JITed code anyway or you want to livepatch 
> the callees of it?

So the rule is that if frame pointers are enabled all kernel code should have 
correct stack frames - in case an IRQ (or NMI) hits it or it crashes.

Thanks,

	Ingo