linux-kernel - Re: [RFC] Clarification for “undefined behaviour”?

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Message-ID: <4c489b64-4c25-43e3-90d3-37f2f335d665@stanley.mountain>
Date: Wed, 5 Mar 2025 11:51:59 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Markus Elfring <Markus.Elfring@....de>
Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	kernel-janitors@...r.kernel.org, freedreno@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
	Abhinav Kumar <quic_abhinavk@...cinc.com>,
	Archit Taneja <architt@...eaurora.org>,
	Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...il.com>,
	Jeykumar Sankaran <jsanka@...eaurora.org>,
	Jordan Crouse <jordan@...micpenguin.net>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
	Simona Vetter <simona@...ll.ch>, Vinod Koul <vkoul@...nel.org>,
	cocci@...ia.fr, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Clarification for “undefined behaviour”?

On Wed, Mar 05, 2025 at 09:40:43AM +0100, Markus Elfring wrote:
> >>> The address of a data structure member was determined before
> >>> a corresponding null pointer check in the implementation of
> >>> the functions “dpu_hw_pp_enable_te” and “dpu_hw_pp_get_vsync_info”.
> >>>
> >>> Thus avoid the risk for undefined behaviour by removing extra
> >>> initialisations for the variable “c” (also because it was already
> >>> reassigned with the same value behind this pointer check).
> > There is no undefined behavior here.
> 
> Is there a need to improve the wording precision?
> 
> There are words which denote a special meaning according to aspects of
> the programming language “C”.
> https://en.cppreference.com/w/c/language/behavior
> 
> Dereferences of null pointers are treated in special ways.

This not a dereference.  It's just pointer math.

regards,
dan carpenter