RE: [PATCH 1/3] drm/amdgpu: fix stack alignment ABI mismatch for Clang

[S, Shirish]

Tested-by: Shirish S <shirish.s@xxxxxxx> 



Regards,
Shirish S

-----Original Message-----
From: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> 
Sent: Thursday, October 17, 2019 4:32 AM
To: Wentland, Harry <Harry.Wentland@xxxxxxx>; Deucher, Alexander <Alexander.Deucher@xxxxxxx>
Cc: yshuiv7@xxxxxxxxx; andrew.cooper3@xxxxxxxxxx; arnd@xxxxxxxx; clang-built-linux@xxxxxxxxxxxxxxxx; mka@xxxxxxxxxx; S, Shirish <Shirish.S@xxxxxxx>; Zhou, David(ChunMing) <David1.Zhou@xxxxxxx>; Koenig, Christian <Christian.Koenig@xxxxxxx>; amd-gfx@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
Subject: [PATCH 1/3] drm/amdgpu: fix stack alignment ABI mismatch for Clang

The x86 kernel is compiled with an 8B stack alignment via `-mpreferred-stack-boundary=3` for GCC since 3.6-rc1 via commit d9b0cde91c60 ("x86-64, gcc: Use -mpreferred-stack-boundary=3 if supported") or `-mstack-alignment=8` for Clang. Parts of the AMDGPU driver are compiled with 16B stack alignment.

Generally, the stack alignment is part of the ABI. Linking together two different translation units with differing stack alignment is dangerous, particularly when the translation unit with the smaller stack alignment makes calls into the translation unit with the larger stack alignment.
While 8B aligned stacks are sometimes also 16B aligned, they are not always.

Multiple users have reported General Protection Faults (GPF) when using the AMDGPU driver compiled with Clang. Clang is placing objects in stack slots assuming the stack is 16B aligned, and selecting instructions that require 16B aligned memory operands.

At runtime, syscall handlers with 8B aligned stack call into code that assumes 16B stack alignment.  When the stack is a multiple of 8B but not 16B, these instructions result in a GPF.

Remove the code that added compatibility between the differing compiler flags, as it will result in runtime GPFs when built with Clang. Cleanups for GCC will be sent in later patches in the series.

Link: https://github.com/ClangBuiltLinux/linux/issues/735
Debugged-by: Yuxuan Shui <yshuiv7@xxxxxxxxx>
Reported-by: Shirish S <shirish.s@xxxxxxx>
Reported-by: Yuxuan Shui <yshuiv7@xxxxxxxxx>
Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
---
 drivers/gpu/drm/amd/display/dc/calcs/Makefile | 10 ++++------  drivers/gpu/drm/amd/display/dc/dcn20/Makefile | 10 ++++------  drivers/gpu/drm/amd/display/dc/dcn21/Makefile | 10 ++++------
 drivers/gpu/drm/amd/display/dc/dml/Makefile   | 10 ++++------
 drivers/gpu/drm/amd/display/dc/dsc/Makefile   | 10 ++++------
 5 files changed, 20 insertions(+), 30 deletions(-)

diff --git a/drivers/gpu/drm/amd/display/dc/calcs/Makefile b/drivers/gpu/drm/amd/display/dc/calcs/Makefile
index 985633c08a26..4b1a8a08a5de 100644
--- a/drivers/gpu/drm/amd/display/dc/calcs/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/calcs/Makefile
@@ -24,13 +24,11 @@
 # It calculates Bandwidth and Watermarks values for HW programming  #
 
-ifneq ($(call cc-option, -mpreferred-stack-boundary=4),)
-	cc_stack_align := -mpreferred-stack-boundary=4
-else ifneq ($(call cc-option, -mstack-alignment=16),)
-	cc_stack_align := -mstack-alignment=16
-endif
+calcs_ccflags := -mhard-float -msse
 
-calcs_ccflags := -mhard-float -msse $(cc_stack_align)
+ifdef CONFIG_CC_IS_GCC
+calcs_ccflags += -mpreferred-stack-boundary=4 endif
 
 ifdef CONFIG_CC_IS_CLANG
 calcs_ccflags += -msse2
diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/Makefile b/drivers/gpu/drm/amd/display/dc/dcn20/Makefile
index ddb8d5649e79..5fe3eb80075d 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn20/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dcn20/Makefile
@@ -10,13 +10,11 @@ ifdef CONFIG_DRM_AMD_DC_DSC_SUPPORT
 DCN20 += dcn20_dsc.o
 endif
 
-ifneq ($(call cc-option, -mpreferred-stack-boundary=4),)
-	cc_stack_align := -mpreferred-stack-boundary=4
-else ifneq ($(call cc-option, -mstack-alignment=16),)
-	cc_stack_align := -mstack-alignment=16
-endif
+CFLAGS_$(AMDDALPATH)/dc/dcn20/dcn20_resource.o := -mhard-float -msse
 
-CFLAGS_$(AMDDALPATH)/dc/dcn20/dcn20_resource.o := -mhard-float -msse $(cc_stack_align)
+ifdef CONFIG_CC_IS_GCC
+CFLAGS_$(AMDDALPATH)/dc/dcn20/dcn20_resource.o += 
+-mpreferred-stack-boundary=4 endif
 
 ifdef CONFIG_CC_IS_CLANG
 CFLAGS_$(AMDDALPATH)/dc/dcn20/dcn20_resource.o += -msse2 diff --git a/drivers/gpu/drm/amd/display/dc/dcn21/Makefile b/drivers/gpu/drm/amd/display/dc/dcn21/Makefile
index ef673bffc241..7057e20748b9 100644
--- a/drivers/gpu/drm/amd/display/dc/dcn21/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dcn21/Makefile
@@ -3,13 +3,11 @@
 
 DCN21 = dcn21_hubp.o dcn21_hubbub.o dcn21_resource.o
 
-ifneq ($(call cc-option, -mpreferred-stack-boundary=4),)
-	cc_stack_align := -mpreferred-stack-boundary=4
-else ifneq ($(call cc-option, -mstack-alignment=16),)
-	cc_stack_align := -mstack-alignment=16
-endif
+CFLAGS_$(AMDDALPATH)/dc/dcn21/dcn21_resource.o := -mhard-float -msse
 
-CFLAGS_$(AMDDALPATH)/dc/dcn21/dcn21_resource.o := -mhard-float -msse $(cc_stack_align)
+ifdef CONFIG_CC_IS_GCC
+CFLAGS_$(AMDDALPATH)/dc/dcn21/dcn21_resource.o += 
+-mpreferred-stack-boundary=4 endif
 
 ifdef CONFIG_CC_IS_CLANG
 CFLAGS_$(AMDDALPATH)/dc/dcn21/dcn21_resource.o += -msse2 diff --git a/drivers/gpu/drm/amd/display/dc/dml/Makefile b/drivers/gpu/drm/amd/display/dc/dml/Makefile
index 5b2a65b42403..1bd6e307b7f8 100644
--- a/drivers/gpu/drm/amd/display/dc/dml/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dml/Makefile
@@ -24,13 +24,11 @@
 # It provides the general basic services required by other DAL  # subcomponents.
 
-ifneq ($(call cc-option, -mpreferred-stack-boundary=4),)
-	cc_stack_align := -mpreferred-stack-boundary=4
-else ifneq ($(call cc-option, -mstack-alignment=16),)
-	cc_stack_align := -mstack-alignment=16
-endif
+dml_ccflags := -mhard-float -msse
 
-dml_ccflags := -mhard-float -msse $(cc_stack_align)
+ifdef CONFIG_CC_IS_GCC
+dml_ccflags += -mpreferred-stack-boundary=4 endif
 
 ifdef CONFIG_CC_IS_CLANG
 dml_ccflags += -msse2
diff --git a/drivers/gpu/drm/amd/display/dc/dsc/Makefile b/drivers/gpu/drm/amd/display/dc/dsc/Makefile
index b456cd23c6fa..932c3055230e 100644
--- a/drivers/gpu/drm/amd/display/dc/dsc/Makefile
+++ b/drivers/gpu/drm/amd/display/dc/dsc/Makefile
@@ -1,13 +1,11 @@
 #
 # Makefile for the 'dsc' sub-component of DAL.
 
-ifneq ($(call cc-option, -mpreferred-stack-boundary=4),)
-	cc_stack_align := -mpreferred-stack-boundary=4
-else ifneq ($(call cc-option, -mstack-alignment=16),)
-	cc_stack_align := -mstack-alignment=16
-endif
+dsc_ccflags := -mhard-float -msse
 
-dsc_ccflags := -mhard-float -msse $(cc_stack_align)
+ifdef CONFIG_CC_IS_GCC
+dsc_ccflags += -mpreferred-stack-boundary=4 endif
 
 ifdef CONFIG_CC_IS_CLANG
 dsc_ccflags += -msse2
--
2.23.0.700.g56cf767bdb-goog