[PATCH v2] drm/amd/display: Increase frame warning limit with KASAN or KCSAN in dml2

[Alex Deucher]

On Thu, Nov 2, 2023 at 1:41 PM Nathan Chancellor <nathan at kernel.org> wrote:
>
> When building ARCH=x86_64 allmodconfig with clang, which will typically
> have sanitizers enabled, there is a warning about a large stack frame.
>
>   drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/display_mode_core.c:6265:13: error: stack frame size (2520) exceeds limit (2048) in 'dml_prefetch_check' [-Werror,-Wframe-larger-than]
>    6265 | static void dml_prefetch_check(struct display_mode_lib_st *mode_lib)
>         |             ^
>   1 error generated.
>
> Notably, GCC 13.2.0 does not do too much of a better job, as it is right
> at the current limit of 2048 (and others have reported being over with
> older GCC versions):
>
>   drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/display_mode_core.c: In function 'dml_prefetch_check':
>   drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/display_mode_core.c:6705:1: error: the frame size of 2048 bytes is larger than 1800 bytes [-Werror=frame-larger-than=]
>    6705 | }
>         | ^
>
> In the past, these warnings have been avoided by reducing the number of
> parameters to various functions so that not as many arguments need to be
> passed on the stack. However, these patches take a good amount of effort
> to write despite being mechanical due to code structure and complexity
> and they are never carried forward to new generations of the code so
> that effort has to be expended every new hardware generation, which
> becomes harder to justify as time goes on.
>
> To avoid having a noticeable or lengthy breakage in all{mod,yes}config,
> which are easy testing targets that have -Werror enabled, increase the
> limit for configurations that have KASAN or KCSAN enabled by 50% so that
> cases of extremely poor code generation can still be caught while not
> breaking the majority of builds. CONFIG_KMSAN also causes high stack
> usage but the frame limit is already set to zero when it is enabled,
> which is accounted for by the check for CONFIG_FRAME_WARN=0 in the dml2
> Makefile.
>
> Signed-off-by: Nathan Chancellor <nathan at kernel.org>
> ---
> If there is another DRM pull before 6.7-rc1, it would be much
> appreciated if this could make that so that other trees are not
> potentially broken by this. If not, no worries, as it was my fault for
> not sending this sooner.

Applied.  Thanks!  Will send out a PR this week.

Alex


>
> Changes in v2:
> - Adjust workaround to check for either CONFIG_KASAN=y or
>   CONFIG_KCSAN=y, as the same problem has been reported with older
>   versions of GCC (Hamza, Alex)
> - Link to v1: https://lore.kernel.org/r/20231102-amdgpu-dml2-increase-frame-size-warning-for-clang-v1-1-6eb157352931@kernel.org
> ---
>  drivers/gpu/drm/amd/display/dc/dml2/Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/dml2/Makefile b/drivers/gpu/drm/amd/display/dc/dml2/Makefile
> index 70ae5eba624e..acff3449b8d7 100644
> --- a/drivers/gpu/drm/amd/display/dc/dml2/Makefile
> +++ b/drivers/gpu/drm/amd/display/dc/dml2/Makefile
> @@ -60,8 +60,12 @@ endif
>  endif
>
>  ifneq ($(CONFIG_FRAME_WARN),0)
> +ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)),y)
> +frame_warn_flag := -Wframe-larger-than=3072
> +else
>  frame_warn_flag := -Wframe-larger-than=2048
>  endif
> +endif
>
>  CFLAGS_$(AMDDALPATH)/dc/dml2/display_mode_core.o := $(dml2_ccflags) $(frame_warn_flag)
>  CFLAGS_$(AMDDALPATH)/dc/dml2/display_mode_util.o := $(dml2_ccflags)
>
> ---
> base-commit: 21e80f3841c01aeaf32d7aee7bbc87b3db1aa0c6
> change-id: 20231102-amdgpu-dml2-increase-frame-size-warning-for-clang-c93bd2d6a871
>
> Best regards,
> --
> Nathan Chancellor <nathan at kernel.org>
>