[PATCH] drm/amd/display: Fix sanitizer check for the DML frame size limit

[PATCH] drm/amd/display: Fix sanitizer check for the DML frame size limit

[Sasha Levin]

Building x86_64 allmodconfig with clang fails:

  .../dml2_0/dml21/src/dml2_core/dml2_core_dcn4_calcs.c:10491:13:
  error: stack frame size (3128) exceeds limit (3072) in
  'dml_core_mode_programming' [-Werror,-Wframe-larger-than]

That config enables both KASAN and UBSAN, and should get the 4096
byte limit meant for clang COMPILE_TEST sanitizer builds. The check
in the dml and dml2_0 Makefiles concatenates the three symbols with
no separator:

  ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)$(CONFIG_UBSAN)),y)

KASAN and KCSAN cannot be enabled together, so before UBSAN was
added the string was at most "y". UBSAN can be enabled alongside
either of them, and with both set the string becomes "yy",
$(filter y,yy) is empty, and the build falls through to the
non-sanitizer limit of 3072. Adding UBSAN to the check therefore
lowered the limit for the most heavily instrumented builds instead
of raising it.

Separate the symbols with spaces so that $(filter) sees individual
words, and test for a non-empty result. Only the configs with two
sanitizers enabled change behaviour.

Found by KernelCI builds of the linus-next tree.

Fixes: ebf8b0fd8508 ("drm/amd/display: Relax DML frame limit with UBSAN")
Assisted-by: LLM
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/amd/display/dc/dml/Makefile    | 2 +-
 drivers/gpu/drm/amd/display/dc/dml2_0/Makefile | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/dml/Makefile b/drivers/gpu/drm/amd/display/dc/dml/Makefile
index 91465ac05c971..eb4ce5b1ecfbb 100644
--- a/drivers/gpu/drm/amd/display/dc/dml/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dml/Makefile
@@ -29,7 +29,7 @@ dml_ccflags := $(CC_FLAGS_FPU)
 dml_rcflags := $(CC_FLAGS_NO_FPU)
 
 ifneq ($(CONFIG_FRAME_WARN),0)
-    ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)$(CONFIG_UBSAN)),y)
+    ifneq ($(filter y,$(CONFIG_KASAN) $(CONFIG_KCSAN) $(CONFIG_UBSAN)),)
         ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_COMPILE_TEST),yy)
             frame_warn_limit := 4096
         else
diff --git a/drivers/gpu/drm/amd/display/dc/dml2_0/Makefile b/drivers/gpu/drm/amd/display/dc/dml2_0/Makefile
index e8bd061be05c1..2181079c89d0e 100644
--- a/drivers/gpu/drm/amd/display/dc/dml2_0/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dml2_0/Makefile
@@ -28,7 +28,7 @@ dml2_ccflags := $(CC_FLAGS_FPU)
 dml2_rcflags := $(CC_FLAGS_NO_FPU)
 
 ifneq ($(CONFIG_FRAME_WARN),0)
-    ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)$(CONFIG_UBSAN)),y)
+    ifneq ($(filter y,$(CONFIG_KASAN) $(CONFIG_KCSAN) $(CONFIG_UBSAN)),)
         ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_COMPILE_TEST),yy)
             frame_warn_limit := 4096
         else
-- 
2.53.0

Re: [PATCH] drm/amd/display: Fix sanitizer check for the DML frame size limit

[Alex Deucher]

Applied.  Thanks.  Will include this in my -fixes PR later this week.

Alex

On Sun, Sep 27, 2026 at 12:26 PM Sasha Levin <sashal@kernel.org> wrote:
>
> Building x86_64 allmodconfig with clang fails:
>
>   .../dml2_0/dml21/src/dml2_core/dml2_core_dcn4_calcs.c:10491:13:
>   error: stack frame size (3128) exceeds limit (3072) in
>   'dml_core_mode_programming' [-Werror,-Wframe-larger-than]
>
> That config enables both KASAN and UBSAN, and should get the 4096
> byte limit meant for clang COMPILE_TEST sanitizer builds. The check
> in the dml and dml2_0 Makefiles concatenates the three symbols with
> no separator:
>
>   ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)$(CONFIG_UBSAN)),y)
>
> KASAN and KCSAN cannot be enabled together, so before UBSAN was
> added the string was at most "y". UBSAN can be enabled alongside
> either of them, and with both set the string becomes "yy",
> $(filter y,yy) is empty, and the build falls through to the
> non-sanitizer limit of 3072. Adding UBSAN to the check therefore
> lowered the limit for the most heavily instrumented builds instead
> of raising it.
>
> Separate the symbols with spaces so that $(filter) sees individual
> words, and test for a non-empty result. Only the configs with two
> sanitizers enabled change behaviour.
>
> Found by KernelCI builds of the linus-next tree.
>
> Fixes: ebf8b0fd8508 ("drm/amd/display: Relax DML frame limit with UBSAN")
> Assisted-by: LLM
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  drivers/gpu/drm/amd/display/dc/dml/Makefile    | 2 +-
>  drivers/gpu/drm/amd/display/dc/dml2_0/Makefile | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dc/dml/Makefile b/drivers/gpu/drm/amd/display/dc/dml/Makefile
> index 91465ac05c971..eb4ce5b1ecfbb 100644
> --- a/drivers/gpu/drm/amd/display/dc/dml/Makefile
> +++ b/drivers/gpu/drm/amd/display/dc/dml/Makefile
> @@ -29,7 +29,7 @@ dml_ccflags := $(CC_FLAGS_FPU)
>  dml_rcflags := $(CC_FLAGS_NO_FPU)
>
>  ifneq ($(CONFIG_FRAME_WARN),0)
> -    ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)$(CONFIG_UBSAN)),y)
> +    ifneq ($(filter y,$(CONFIG_KASAN) $(CONFIG_KCSAN) $(CONFIG_UBSAN)),)
>          ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_COMPILE_TEST),yy)
>              frame_warn_limit := 4096
>          else
> diff --git a/drivers/gpu/drm/amd/display/dc/dml2_0/Makefile b/drivers/gpu/drm/amd/display/dc/dml2_0/Makefile
> index e8bd061be05c1..2181079c89d0e 100644
> --- a/drivers/gpu/drm/amd/display/dc/dml2_0/Makefile
> +++ b/drivers/gpu/drm/amd/display/dc/dml2_0/Makefile
> @@ -28,7 +28,7 @@ dml2_ccflags := $(CC_FLAGS_FPU)
>  dml2_rcflags := $(CC_FLAGS_NO_FPU)
>
>  ifneq ($(CONFIG_FRAME_WARN),0)
> -    ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)$(CONFIG_UBSAN)),y)
> +    ifneq ($(filter y,$(CONFIG_KASAN) $(CONFIG_KCSAN) $(CONFIG_UBSAN)),)
>          ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_COMPILE_TEST),yy)
>              frame_warn_limit := 4096
>          else
> --
> 2.53.0
>