linux-kernel - Re: [PATCH 15/20] drm/tegra/hub: Increase buffer size to ensure all possible values can be stored

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Message-ID: <87r0ns4weq.fsf@intel.com>
Date:   Thu, 24 Aug 2023 12:33:33 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee@...nel.org>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Jonathan Hunter <jonathanh@...dia.com>,
        linux-tegra@...r.kernel.org,
        Mikko Perttunen <mperttunen@...dia.com>
Subject: Re: [PATCH 15/20] drm/tegra/hub: Increase buffer size to ensure all
 possible values can be stored

On Thu, 24 Aug 2023, Thierry Reding <thierry.reding@...il.com> wrote:
> On Thu, Aug 24, 2023 at 08:37:00AM +0100, Lee Jones wrote:
>> When converting from int to string, we must allow for up to 10-chars (2147483647).
>> 
>> Fixes the following W=1 kernel build warning(s):
>> 
>>  drivers/gpu/drm/tegra/hub.c: In function ‘tegra_display_hub_probe’:
>>  drivers/gpu/drm/tegra/hub.c:1106:47: warning: ‘%u’ directive output may be truncated writing between 1 and 10 bytes into a region of size 4 [-Wformat-truncation=]
>>  drivers/gpu/drm/tegra/hub.c:1106:42: note: directive argument in the range [0, 4294967294]
>>  drivers/gpu/drm/tegra/hub.c:1106:17: note: ‘snprintf’ output between 6 and 15 bytes into a destination of size 8
>
> I wish there was (perhaps there is?) a better way to annotate that i
> will always be within a given range. In practice this is always going to
> be smaller than 10 and even in future hardware I wouldn't expect this to
> ever exceed anything like 32 or 64, so 8 characters is already generous.

I assume you could do

	snprintf(id, sizeof(id), "wgrp%u", (unsigned char)i);

but it's perhaps less obvious than just increasing the size of the
buffer.

BR,
Jani.

>
> Thierry
>
>> 
>> Signed-off-by: Lee Jones <lee@...nel.org>
>> ---
>> Cc: Thierry Reding <thierry.reding@...il.com>
>> Cc: Mikko Perttunen <mperttunen@...dia.com>
>> Cc: David Airlie <airlied@...il.com>
>> Cc: Daniel Vetter <daniel@...ll.ch>
>> Cc: Jonathan Hunter <jonathanh@...dia.com>
>> Cc: Philipp Zabel <p.zabel@...gutronix.de>
>> Cc: dri-devel@...ts.freedesktop.org
>> Cc: linux-tegra@...r.kernel.org
>> ---
>>  drivers/gpu/drm/tegra/hub.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/tegra/hub.c b/drivers/gpu/drm/tegra/hub.c
>> index 1af5f8318d914..f21e57e8599ee 100644
>> --- a/drivers/gpu/drm/tegra/hub.c
>> +++ b/drivers/gpu/drm/tegra/hub.c
>> @@ -1101,7 +1101,7 @@ static int tegra_display_hub_probe(struct platform_device *pdev)
>>  
>>  	for (i = 0; i < hub->soc->num_wgrps; i++) {
>>  		struct tegra_windowgroup *wgrp = &hub->wgrps[i];
>> -		char id[8];
>> +		char id[16];
>>  
>>  		snprintf(id, sizeof(id), "wgrp%u", i);
>>  		mutex_init(&wgrp->lock);
>> -- 
>> 2.42.0.rc1.204.g551eb34607-goog
>> 

-- 
Jani Nikula, Intel Open Source Graphics Center