Re: [PATCH] drm/edid: reduce update_display_info() stack usage

[Jani Nikula <jani.nikula@intel.com>]

On Mon, 19 Oct 2026, "Arnd Bergmann" <arnd@arndb.de> wrote:
> On Mon, Oct 19, 2026, at 15:28, Jani Nikula wrote:
>> On Tue, 13 Oct 2026, Arnd Bergmann <arnd@kernel.org> wrote:
>>> From: Arnd Bergmann <arnd@arndb.de>
>>>
>>> The drm_parse_cea_ext() calls into nine individual parser functions
>>> based on the data format. If all of those get inlined and KASAN_STACK
>>> is enabled, this can explode the combined stack usage beyond a
>>> reasonable amount:
>>>
>>> drivers/gpu/drm/drm_edid.c: In function 'update_display_info':
>>> drivers/gpu/drm/drm_edid.c:7040:1: error: the frame size of 1888 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]
>>>  7040 | }
>>>       | ^
>>>
>>> Mark all of the individual parser functions as noinline_for_stack
>>> to avoid this and keep their stack frames separate. This reduces
>>> the stack usage for update_display_info/drm_parse_cea_ext to
>>> a more manageable 744 bytes, while each parser only adds at most
>>> 200 bytes on top.
>>
>> Is there really no way to tell the compiler to not do silly things in a
>> more generic way?
>
> The problem is really the sanitizers here, which turn off the
> optimizations that gcc relies on for its normal behavior and
> which cause additional register pressure for the inserted function
> calls.

Cc: a bunch of KASAN folks.

I think it's really silly and ugly to have to sprinkle
noinline_for_stack all over the place in pretty normal code [1]. The
stack usage for each individual function is fairly small.


BR,
Jani.


[1] https://lore.kernel.org/r/20261013205223.2396822-1-arnd@kernel.org


-- 
Jani Nikula, Intel