From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Andi Kleen <ak@linux.intel.com>,
tglx@linutronix.de, torvalds@linux-foundation.org,
gregkh@linux-foundation.org, linux-kernel@vger.kernel.org,
tim.c.chen@linux.intel.com
Subject: Re: [PATCH v2 11/12] retpoline/objtool: Disable some objtool warnings
Date: Thu, 4 Jan 2018 10:32:52 -0600 [thread overview]
Message-ID: <20180104163252.jkc44bopf5yifbbc@treble> (raw)
In-Reply-To: <20180104161308.zvudrggt6755ls5i@two.firstfloor.org>
On Thu, Jan 04, 2018 at 08:13:08AM -0800, Andi Kleen wrote:
> On Thu, Jan 04, 2018 at 10:06:01AM -0600, Josh Poimboeuf wrote:
> > On Thu, Jan 04, 2018 at 07:59:14AM -0800, Andi Kleen wrote:
> > > > NAK. We can't blindly disable objtool warnings, that will break
> > > > livepatch and the ORC unwinder. If you share a .o file (or the GCC
> > > > code) I can look at adding retpoline support.
> > >
> > > I don't think we can wait for that. We can disable livepatch and the
> > > unwinder for now. They are not essential. Frame pointers should work
> > > well enough for unwinding
> >
> > If you want to make this feature conflict with livepatch and ORC,
> > silencing objtool warnings is not the way to do it.
>
> I don't see why it would conflict with the unwinder anyways?
>
> It doesn't change the long term stack state, so it should be invisible to the
> unwinder (unless you crash in the thunk, which is very unlikely)
>
> I actually got some unwinder backtraces during development and they seemed
> to work.
Those objtool warnings are places where ORC annotations are either
missing or wrong.
At the very least, this needs to conflict with HAVE_RELIABLE_STACKTRACE
and HAVE_STACK_VALIDATION until objtool can understand the new code.
Currently ORC relies on HAVE_STACK_VALIDATION, so CONFIG_UNWINDER_ORC
would need to be disabled as well.
> > > and afaik nobody can use livepatch in mainline anyways.
> >
> > Why not? The patch creation tooling is still out-of-tree, but livepatch
> > itself is fully supported in mainline.
>
> Ok.
>
> Still doesn't seem critical at this point if it's some out of tree
> thing.
There are many livepatch users out there who would disagree. The
out-of-tree bits aren't in kernel space. If your patches are ready
before objtool supports them, then fine, make them conflict with
objtool. But please don't introduce silent breakage.
Either way we'll need to figure out a way to get objtool support ASAP.
--
Josh
next prev parent reply other threads:[~2018-01-04 16:33 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-04 2:00 Avoid speculative indirect calls in kernel Andi Kleen
2018-01-04 2:00 ` [PATCH v2 01/12] x86/retpoline: Define retpoline indirect thunk and macros Andi Kleen
2018-01-04 2:15 ` Brian Gerst
2018-01-04 2:32 ` Alan Cox
2018-01-04 2:00 ` [PATCH v2 02/12] x86/retpoline/crypto: Convert crypto assembler indirect jumps Andi Kleen
2018-01-04 2:00 ` [PATCH v2 03/12] x86/retpoline/entry: Convert entry " Andi Kleen
2018-01-04 8:42 ` David Woodhouse
2018-01-04 2:00 ` [PATCH v2 04/12] x86/retpoline/ftrace: Convert ftrace " Andi Kleen
2018-01-04 2:00 ` [PATCH v2 05/12] x86/retpoline/hyperv: Convert " Andi Kleen
2018-01-04 2:00 ` [PATCH v2 06/12] x86/retpoline/crypto: Convert xen " Andi Kleen
2018-01-04 6:48 ` Juergen Gross
2018-01-04 6:50 ` Andi Kleen
2018-01-04 2:00 ` [PATCH v2 07/12] x86/retpoline/checksum32: Convert " Andi Kleen
2018-01-04 2:00 ` [PATCH v2 08/12] x86/retpoline/irq32: " Andi Kleen
2018-01-04 2:00 ` [PATCH v2 09/12] x86/retpoline: Finally enable retpoline for C code Andi Kleen
2018-01-04 2:00 ` [PATCH v2 10/12] retpoline/taint: Taint kernel for missing retpoline in compiler Andi Kleen
2018-01-04 2:00 ` [PATCH v2 11/12] retpoline/objtool: Disable some objtool warnings Andi Kleen
2018-01-04 14:38 ` Josh Poimboeuf
2018-01-04 14:46 ` David Woodhouse
2018-01-04 15:59 ` Andi Kleen
2018-01-04 16:06 ` Josh Poimboeuf
2018-01-04 16:13 ` Andi Kleen
2018-01-04 16:32 ` Josh Poimboeuf [this message]
2018-01-04 17:35 ` Josh Poimboeuf
2018-01-04 2:00 ` [PATCH v2 12/12] retpoline: Attempt to quiten objtool warning for unreachable code Andi Kleen
2018-01-04 11:49 ` Avoid speculative indirect calls in kernel Pavel Machek
2018-01-04 12:09 ` Alan Cox
2018-01-04 13:32 ` Pavel Machek
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