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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Mark Brown <broonie@kernel.org>,
	linux-kernel@vger.kernel.org, Jiri Kosina <jikos@kernel.org>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Jonathan Corbet <corbet@lwn.net>, Miroslav Benes <mbenes@suse.cz>,
	Petr Mladek <pmladek@suse.com>,
	linux-doc@vger.kernel.org, live-patching@vger.kernel.org
Subject: Re: [PATCH] Documentation: livepatch: document reliable stacktrace
Date: Thu, 14 Jan 2021 18:03:59 -0600	[thread overview]
Message-ID: <20210115000359.dxzivd7hvqvhkqji@treble> (raw)
In-Reply-To: <20210114181013.GE2739@C02TD0UTHF1T.local>

On Thu, Jan 14, 2021 at 06:10:13PM +0000, Mark Rutland wrote:
> On Wed, Jan 13, 2021 at 04:25:41PM -0600, Josh Poimboeuf wrote:
> > On Wed, Jan 13, 2021 at 08:23:15PM +0000, Mark Brown wrote:
> > > On Wed, Jan 13, 2021 at 01:33:13PM -0600, Josh Poimboeuf wrote:
> > > 
> > > > I think it's worth mentioning a little more about objtool.  There are a
> > > > few passing mentions of objtool's generation of metadata (i.e. ORC), but
> > > > objtool has another relevant purpose: stack validation.  That's
> > > > particularly important when it comes to frame pointers.
> > > 
> > > > For some architectures like x86_64 and arm64 (but not powerpc/s390),
> > > > it's far too easy for a human to write asm and/or inline asm which
> > > > violates frame pointer protocol, silently causing the violater's callee
> > > > to get skipped in the unwind.  Such architectures need objtool
> > > > implemented for CONFIG_STACK_VALIDATION.
> > > 
> > > This basically boils down to just adding a statement saying "you may
> > > need to depend on objtool" I think?
> > 
> > Right, but maybe it would be a short paragraph or two.
> 
> I reckon that's a top-level section between requirements and
> consideration along the lines of:
> 
> 3. Compile-time analysis
> ========================
> 
> To ensure that kernel code can be correctly unwound in all cases,
> architectures may need to verify that code has been compiled in a manner
> expected by the unwinder. For example, an unwinder may expect that
> functions manipulate the stack pointer in a limited way, or that all
> functions use specific prologue and epilogue sequences. Architectures
> with such requirements should verify the kernel compilation using
> objtool.
> 
> In some cases, an unwinder may require metadata to correctly unwind.
> Where necessary, this metadata should be generated at build time using
> objtool.

Sounds good to me.

-- 
Josh


  reply	other threads:[~2021-01-15  0:05 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-13 16:57 [PATCH] Documentation: livepatch: document reliable stacktrace Mark Brown
2021-01-13 19:33 ` Josh Poimboeuf
2021-01-13 20:23   ` Mark Brown
2021-01-13 22:25     ` Josh Poimboeuf
2021-01-14 18:10       ` Mark Rutland
2021-01-15  0:03         ` Josh Poimboeuf [this message]
2021-01-14 11:54   ` Mark Rutland
2021-01-14 14:36     ` Josh Poimboeuf
2021-01-14 17:49       ` Mark Rutland
2021-01-14 20:03         ` Josh Poimboeuf
  -- strict thread matches above, loose matches on Subject: below --
2020-10-23 15:35 Mark Rutland
2020-10-27 11:16 ` Petr Mladek
2020-10-29 10:04 ` Miroslav Benes

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