[PATCH] drm/amd/display: Increase sanitizer frame larger than limit when compile testing with clang

[Nathan Chancellor]

Commit 24909d9ec7c3 ("drm/amd/display: Overwriting dualDPP UBF values
before usage") added a new warning in dml2/display_mode_core.c when
building allmodconfig with clang:

  drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/display_mode_core.c:6268:13: error: stack frame size (3128) exceeds limit (3072) in 'dml_prefetch_check' [-Werror,-Wframe-larger-than]
   6268 | static void dml_prefetch_check(struct display_mode_lib_st *mode_lib)
        |             ^

Commit be4e3509314a ("drm/amd/display: DML21 Reintegration For Various
Fixes") introduced one in dml2_core/dml2_core_dcn4_calcs.c with the same
configuration:

  drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/dml21/src/dml2_core/dml2_core_dcn4_calcs.c:7236:13: error: stack frame size (3256) exceeds limit (3072) in 'dml_core_mode_support' [-Werror,-Wframe-larger-than]
   7236 | static bool dml_core_mode_support(struct dml2_core_calcs_mode_support_ex *in_out_params)
        |             ^

In the case of the first warning, the stack usage was already at the
limit at the parent change, so the offending change was rather
innocuous. In the case of the second warning, there was a rather
dramatic increase in stack usage compared to the parent:

  drivers/gpu/drm/amd/amdgpu/../display/dc/dml2/dml21/src/dml2_core/dml2_core_dcn4_calcs.c:7032:13: error: stack frame size (2696) exceeds limit (2048) in 'dml_core_mode_support' [-Werror,-Wframe-larger-than]
   7032 | static bool dml_core_mode_support(struct dml2_core_calcs_mode_support_ex *in_out_params)
        |             ^

This is an unfortunate interaction between an issue with stack slot
reuse in LLVM that gets exacerbated by sanitization (which gets enabled
with all{mod,yes}config) and function calls using a much higher number
of parameters than is typical in the kernel, necessitating passing most
of these values on the stack.

While it is possible that there should be source code changes to address
these warnings, this code is difficult to modify for various reasons, as
has been noted in other changes that have occurred for similar reasons,
such as commit 6740ec97bcdb ("drm/amd/display: Increase frame warning
limit with KASAN or KCSAN in dml2").

Increase the frame larger than limit when compile testing with clang and
the sanitizers enabled to avoid this breakage in all{mod,yes}config, as
they are commonly used and valuable testing targets. While it is not the
best to hide this issue, it is not really relevant when compile testing,
as the sanitizers are commonly stressful on optimizations and they are
only truly useful at runtime, which COMPILE_TEST states will not occur
with the current build.

Reported-by: kernel test robot <lkp at intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412121748.chuX4sap-lkp@intel.com/
Signed-off-by: Nathan Chancellor <nathan at 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 d9c27ebe12ee08d6330eb199cd8ca9c8489fa5b2..91c4f3b4bd5f46ac5c1c74f665b06dbe61081917 100644
--- a/drivers/gpu/drm/amd/display/dc/dml2/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dml2/Makefile
@@ -29,7 +29,11 @@ dml2_rcflags := $(CC_FLAGS_NO_FPU)
 
 ifneq ($(CONFIG_FRAME_WARN),0)
 ifeq ($(filter y,$(CONFIG_KASAN)$(CONFIG_KCSAN)),y)
+ifeq ($(CONFIG_CC_IS_CLANG)$(CONFIG_COMPILE_TEST),yy)
+frame_warn_flag := -Wframe-larger-than=4096
+else
 frame_warn_flag := -Wframe-larger-than=3072
+endif
 else
 frame_warn_flag := -Wframe-larger-than=2048
 endif

---
base-commit: 695c2c745e5dff201b75da8a1d237ce403600d04
change-id: 20241219-amdgpu-dml2-address-clang-frame-larger-than-allconfig-f034d9c5118e

Best regards,
-- 
Nathan Chancellor <nathan at kernel.org>