From: Josh Poimboeuf <jpoimboe@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Zack Rusin <zackr@vmware.com>,
linux-kernel@vger.kernel.org, Miroslav Benes <mbenes@suse.cz>,
x86@kernel.org,
VMware Graphics Reviewers <linux-graphics-maintainer@vmware.com>,
kernel test robot <lkp@intel.com>
Subject: Re: [PATCH] drm/vmwgfx: Silence RBP clobber warnings
Date: Fri, 2 Jun 2023 08:32:39 -0700 [thread overview]
Message-ID: <20230602153239.fsug6rgvoxgnrea6@treble> (raw)
In-Reply-To: <20230602151639.GK620383@hirez.programming.kicks-ass.net>
On Fri, Jun 02, 2023 at 05:16:39PM +0200, Peter Zijlstra wrote:
> On Fri, Jun 02, 2023 at 07:56:34AM -0700, Josh Poimboeuf wrote:
> > VMware hypercalls take the RBP register as input. This breaks basic
> > frame pointer convention, as RBP should never be clobbered.
> >
> > So frame pointer unwinding is broken for the instructions surrounding
> > the hypercall with the clobbered RBP. There's nothing that can be done
> > about that. Just tell objtool to ignore it.
> >
>
> That's a pretty horrific ABI, one that violates the oldest x86 calling
> convention in existence.
>
> VMware folks, shame!!
Agreed :-(
BTW, please ignore the patch, I'll be sending a v2.
I realized (with Peter's prodding on IRC) that reliable ORC unwinding
would be broken if the function has a frame pointer. Which can
happen if the function needs an aligned stack.
--
Josh
prev parent reply other threads:[~2023-06-02 15:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-02 14:56 Josh Poimboeuf
2023-06-02 15:16 ` Peter Zijlstra
2023-06-02 15:32 ` Josh Poimboeuf [this message]
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