Re: [PATCH] drm/i195: Fix format string truncation warning

[Tvrtko Ursulin]

On 07/11/2025 16:42, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@xxxxxxxxxx>
>
> GCC notices that the 16-byte uabi_name field could theoretically be too
> small for the formatted string if the instance number exceeds 100.
>
> Given that there are apparently ABI concerns here, this is the minimal
> fix that shuts up the compiler without changing the output or the
> maximum length for existing values < 100.

What would be those ABI concerns? I don't immediately see any.
> drivers/gpu/drm/i915/intel_memory_region.c: In function ‘intel_memory_region_create’:
> drivers/gpu/drm/i915/intel_memory_region.c:273:61: error: ‘%u’ directive output may be truncated writing between 1 and 5 bytes into a region of size between 3 and 11 [-Werror=format-truncation=]
>    273 |         snprintf(mem->uabi_name, sizeof(mem->uabi_name), "%s%u",
>        |                                                             ^~
> drivers/gpu/drm/i915/intel_memory_region.c:273:58: note: directive argument in the range [0, 65535]
>    273 |         snprintf(mem->uabi_name, sizeof(mem->uabi_name), "%s%u",
>        |                                                          ^~~~~~
> drivers/gpu/drm/i915/intel_memory_region.c:273:9: note: ‘snprintf’ output between 7 and 19 bytes into a destination of size 16
>    273 |         snprintf(mem->uabi_name, sizeof(mem->uabi_name), "%s%u",
>        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>    274 |                  intel_memory_type_str(type), instance);
>        |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tursulin@xxxxxxxxxxx>
> Cc: David Airlie <airlied@xxxxxxxxx>
> Cc: Simona Vetter <simona@xxxxxxxx>
> Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx
> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
>
> This is unlikely to be the right fix, but sending a wrong patch is
> usually a better way to elicit a response than just sending a bug
> report.
>
>   drivers/gpu/drm/i915/intel_memory_region.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_memory_region.c b/drivers/gpu/drm/i915/intel_memory_region.c
> index 59bd603e6deb..ad4afcf0c58a 100644
> --- a/drivers/gpu/drm/i915/intel_memory_region.c
> +++ b/drivers/gpu/drm/i915/intel_memory_region.c
> @@ -271,7 +271,7 @@ intel_memory_region_create(struct drm_i915_private *i915,
>   	mem->instance = instance;
>   
>   	snprintf(mem->uabi_name, sizeof(mem->uabi_name), "%s%u",
> -		 intel_memory_type_str(type), instance);
> +		 intel_memory_type_str(type), instance % 100);
It's a theoretical issue only since there is no hardware with a double 
digit number of instances.

But I guess much prettier fix would be to simply grow the buffer.

Also, hm, how come gcc does not find the mem->name vsnprintf from 
intel_memory_region_set_name?

Regards,

Tvrtko

>   
>   	mutex_init(&mem->objects.lock);
>   	INIT_LIST_HEAD(&mem->objects.list);