linux-kernel - Re: [PATCH] drm/vmwgfx: Silence RBP clobber warnings

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Message-ID: <20230602151639.GK620383@hirez.programming.kicks-ass.net>
Date:   Fri, 2 Jun 2023 17:16:39 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...nel.org>
Cc:     Zack Rusin <zackr@...are.com>, linux-kernel@...r.kernel.org,
        Miroslav Benes <mbenes@...e.cz>, x86@...nel.org,
        VMware Graphics Reviewers 
        <linux-graphics-maintainer@...are.com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] drm/vmwgfx: Silence RBP clobber warnings

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!!