linux-kernel - Re: [PATCH] drm/amd/display: avoid stringop-overflow warnings for dp_decide_lane

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Date: Thu, 21 Dec 2023 21:08:59 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Arnd Bergmann <arnd@...nel.org>, Harry Wentland <harry.wentland@....com>,
 Leo Li <sunpeng.li@....com>, Rodrigo Siqueira <Rodrigo.Siqueira@....com>
Cc: Arnd Bergmann <arnd@...db.de>, Alex Deucher <alexander.deucher@....com>,
 Christian König <christian.koenig@....com>,
 "Pan, Xinhui" <Xinhui.Pan@....com>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>, Wenjing Liu <wenjing.liu@....com>,
 Qingqing Zhuo <qingqing.zhuo@....com>, George Shen <george.shen@....com>,
 Jun Lei <Jun.Lei@....com>, Michael Mityushkin <michael.mityushkin@....com>,
 Srinivasan Shanmugam <srinivasan.shanmugam@....com>,
 Alan Liu <haoping.liu@....com>, Michael Strauss <michael.strauss@....com>,
 amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amd/display: avoid stringop-overflow warnings for
 dp_decide_lane_settings()



On 11/22/23 14:13, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> gcc prints a warning about a possible array overflow for a couple of
> callers of dp_decide_lane_settings() after commit 1b56c90018f0 ("Makefile:
> Enable -Wstringop-overflow globally"):
> 
> drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c: In function 'dp_perform_fixed_vs_pe_training_sequence_legacy':
> drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c:426:25: error: 'dp_decide_lane_settings' accessing 4 bytes in a region of size 1 [-Werror=stringop-overflow=]
>   426 |                         dp_decide_lane_settings(lt_settings, dpcd_lane_adjust,
>       |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   427 |                                         lt_settings->hw_lane_settings, lt_settings->dpcd_lane_settings);
>       |                                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/../display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c:426:25: note: referencing argument 4 of type 'union dpcd_training_lane[4]'
> 
> I'm not entirely sure what caused this, but changing the prototype to expect
> a pointer instead of an array avoids the warnings.
> 
> Fixes: 7727e7b60f82 ("drm/amd/display: Improve robustness of FIXED_VS link training at DP1 rates")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>


Acked-by: Randy Dunlap <rdunlap@...radead.org>
Tested-by: Randy Dunlap <rdunlap@...radead.org> # build-tested

Thanks.

> ---
>  .../gpu/drm/amd/display/dc/link/protocols/link_dp_training.c    | 2 +-
>  .../gpu/drm/amd/display/dc/link/protocols/link_dp_training.h    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.c b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.c
> index 90339c2dfd84..5a0b04518956 100644
> --- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.c
> +++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.c
> @@ -807,7 +807,7 @@ void dp_decide_lane_settings(
>  		const struct link_training_settings *lt_settings,
>  		const union lane_adjust ln_adjust[LANE_COUNT_DP_MAX],
>  		struct dc_lane_settings hw_lane_settings[LANE_COUNT_DP_MAX],
> -		union dpcd_training_lane dpcd_lane_settings[LANE_COUNT_DP_MAX])
> +		union dpcd_training_lane *dpcd_lane_settings)
>  {
>  	uint32_t lane;
>  
> diff --git a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.h b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.h
> index 7d027bac8255..851bd17317a0 100644
> --- a/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.h
> +++ b/drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training.h
> @@ -111,7 +111,7 @@ void dp_decide_lane_settings(
>  	const struct link_training_settings *lt_settings,
>  	const union lane_adjust ln_adjust[LANE_COUNT_DP_MAX],
>  	struct dc_lane_settings hw_lane_settings[LANE_COUNT_DP_MAX],
> -	union dpcd_training_lane dpcd_lane_settings[LANE_COUNT_DP_MAX]);
> +	union dpcd_training_lane *dpcd_lane_settings);
>  
>  enum dc_dp_training_pattern decide_cr_training_pattern(
>  		const struct dc_link_settings *link_settings);

-- 
#Randy
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