From c868868f6b6a5272350781f9a19b3a5ba1c00b02 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Wed, 16 Oct 2019 16:02:07 -0700 Subject: 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 Reported-by: Shirish S Reported-by: Yuxuan Shui Suggested-by: Andrew Cooper Signed-off-by: Nick Desaulniers Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/display/dc/dcn20/Makefile | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'drivers/gpu/drm/amd/display/dc/dcn20/Makefile') 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 -- cgit v1.2.3 From 00db297106e81770e7c4319014a67896053b5a22 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Wed, 16 Oct 2019 16:02:08 -0700 Subject: drm/amdgpu: fix stack alignment ABI mismatch for GCC 7.1+ GCC earlier than 7.1 errors when compiling code that makes use of `double`s and sets a stack alignment outside of the range of [2^4-2^12]: $ cat foo.c double foo(double x, double y) { return x + y; } $ gcc-4.9 -mpreferred-stack-boundary=3 foo.c error: -mpreferred-stack-boundary=3 is not between 4 and 12 This is likely why the AMDGPU driver was ever compiled with a different stack alignment (and thus different ABI) than the rest of the x86 kernel. The kernel uses 8B stack alignment, while the driver was using 16B stack alignment in a few places. Since GCC 7.1+ doesn't error, fix the ABI mismatch for users of newer versions of GCC. There was discussion about whether to mark the driver broken or not for users of GCC earlier than 7.1, but since the driver currently is working, don't explicitly break the driver for them here. Relying on differing stack alignment is unspecified behavior, and brittle, and may break in the future. This patch is no functional change for GCC users earlier than 7.1. It's been compile tested on GCC 4.9 and 8.3 to check the correct flags. It should be boot tested when built with GCC 7.1+. -mincoming-stack-boundary= or -mstackrealign may help keep this code building for pre-GCC 7.1 users. The version check for GCC is broken into two conditionals, both because cc-ifversion is currently GCC specific, and it simplifies a subsequent patch. Signed-off-by: Nick Desaulniers Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/display/dc/calcs/Makefile | 9 +++++++++ drivers/gpu/drm/amd/display/dc/dcn20/Makefile | 9 +++++++++ drivers/gpu/drm/amd/display/dc/dcn21/Makefile | 9 +++++++++ drivers/gpu/drm/amd/display/dc/dml/Makefile | 9 +++++++++ drivers/gpu/drm/amd/display/dc/dsc/Makefile | 9 +++++++++ 5 files changed, 45 insertions(+) (limited to 'drivers/gpu/drm/amd/display/dc/dcn20/Makefile') diff --git a/drivers/gpu/drm/amd/display/dc/calcs/Makefile b/drivers/gpu/drm/amd/display/dc/calcs/Makefile index 4b1a8a08a5de..a1af55a86508 100644 --- a/drivers/gpu/drm/amd/display/dc/calcs/Makefile +++ b/drivers/gpu/drm/amd/display/dc/calcs/Makefile @@ -27,6 +27,15 @@ calcs_ccflags := -mhard-float -msse ifdef CONFIG_CC_IS_GCC +ifeq ($(call cc-ifversion, -lt, 0701, y), y) +IS_OLD_GCC = 1 +endif +endif + +ifdef IS_OLD_GCC +# Stack alignment mismatch, proceed with caution. +# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 +# (8B stack alignment). calcs_ccflags += -mpreferred-stack-boundary=4 endif diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/Makefile b/drivers/gpu/drm/amd/display/dc/dcn20/Makefile index 5fe3eb80075d..cb0ac131f74a 100644 --- a/drivers/gpu/drm/amd/display/dc/dcn20/Makefile +++ b/drivers/gpu/drm/amd/display/dc/dcn20/Makefile @@ -13,6 +13,15 @@ endif CFLAGS_$(AMDDALPATH)/dc/dcn20/dcn20_resource.o := -mhard-float -msse ifdef CONFIG_CC_IS_GCC +ifeq ($(call cc-ifversion, -lt, 0701, y), y) +IS_OLD_GCC = 1 +endif +endif + +ifdef IS_OLD_GCC +# Stack alignment mismatch, proceed with caution. +# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 +# (8B stack alignment). CFLAGS_$(AMDDALPATH)/dc/dcn20/dcn20_resource.o += -mpreferred-stack-boundary=4 endif diff --git a/drivers/gpu/drm/amd/display/dc/dcn21/Makefile b/drivers/gpu/drm/amd/display/dc/dcn21/Makefile index 7057e20748b9..f92320ddd27f 100644 --- a/drivers/gpu/drm/amd/display/dc/dcn21/Makefile +++ b/drivers/gpu/drm/amd/display/dc/dcn21/Makefile @@ -6,6 +6,15 @@ DCN21 = dcn21_hubp.o dcn21_hubbub.o dcn21_resource.o CFLAGS_$(AMDDALPATH)/dc/dcn21/dcn21_resource.o := -mhard-float -msse ifdef CONFIG_CC_IS_GCC +ifeq ($(call cc-ifversion, -lt, 0701, y), y) +IS_OLD_GCC = 1 +endif +endif + +ifdef IS_OLD_GCC +# Stack alignment mismatch, proceed with caution. +# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 +# (8B stack alignment). CFLAGS_$(AMDDALPATH)/dc/dcn21/dcn21_resource.o += -mpreferred-stack-boundary=4 endif diff --git a/drivers/gpu/drm/amd/display/dc/dml/Makefile b/drivers/gpu/drm/amd/display/dc/dml/Makefile index 1bd6e307b7f8..ef1bdd20b425 100644 --- a/drivers/gpu/drm/amd/display/dc/dml/Makefile +++ b/drivers/gpu/drm/amd/display/dc/dml/Makefile @@ -27,6 +27,15 @@ dml_ccflags := -mhard-float -msse ifdef CONFIG_CC_IS_GCC +ifeq ($(call cc-ifversion, -lt, 0701, y), y) +IS_OLD_GCC = 1 +endif +endif + +ifdef IS_OLD_GCC +# Stack alignment mismatch, proceed with caution. +# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 +# (8B stack alignment). dml_ccflags += -mpreferred-stack-boundary=4 endif diff --git a/drivers/gpu/drm/amd/display/dc/dsc/Makefile b/drivers/gpu/drm/amd/display/dc/dsc/Makefile index 932c3055230e..3f7840828a9f 100644 --- a/drivers/gpu/drm/amd/display/dc/dsc/Makefile +++ b/drivers/gpu/drm/amd/display/dc/dsc/Makefile @@ -4,6 +4,15 @@ dsc_ccflags := -mhard-float -msse ifdef CONFIG_CC_IS_GCC +ifeq ($(call cc-ifversion, -lt, 0701, y), y) +IS_OLD_GCC = 1 +endif +endif + +ifdef IS_OLD_GCC +# Stack alignment mismatch, proceed with caution. +# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 +# (8B stack alignment). dsc_ccflags += -mpreferred-stack-boundary=4 endif -- cgit v1.2.3 From e8a170ff9a3576730e43c0dbdd27b7cd3dc56848 Mon Sep 17 00:00:00 2001 From: Nick Desaulniers Date: Wed, 16 Oct 2019 16:02:09 -0700 Subject: drm/amdgpu: enable -msse2 for GCC 7.1+ users A final attempt at enabling sse2 for GCC users. Orininally attempted in: commit 10117450735c ("drm/amd/display: add -msse2 to prevent Clang from emitting libcalls to undefined SW FP routines") Reverted due to "reported instability" in: commit 193392ed9f69 ("Revert "drm/amd/display: add -msse2 to prevent Clang from emitting libcalls to undefined SW FP routines"") Re-added just for Clang in: commit 0f0727d971f6 ("drm/amd/display: readd -msse2 to prevent Clang from emitting libcalls to undefined SW FP routines") The original report didn't have enough information to know if the GPF was due to misalignment, but I suspect that it was. (The missing information was the disassembly of the function at the bottom of the trace, to see if the instruction pointer pointed to an instruction with 16B alignment memory operand requirements. The stack trace does show the stack was only 8B but not 16B aligned though, which makes this a strong possibility). Now that the stack misalignment issue has been fixed for users of GCC 7.1+, reattempt adding -msse2. This matches Clang. It will likely never be safe to enable this for pre-GCC 7.1 AND use a 16B aligned stack in these translation units. This is only a functional change for GCC 7.1+ users, and should be boot tested. Link: https://bugs.freedesktop.org/show_bug.cgi?id=109487 Signed-off-by: Nick Desaulniers Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/display/dc/calcs/Makefile | 4 +--- drivers/gpu/drm/amd/display/dc/dcn20/Makefile | 4 +--- drivers/gpu/drm/amd/display/dc/dcn21/Makefile | 4 +--- drivers/gpu/drm/amd/display/dc/dml/Makefile | 4 +--- drivers/gpu/drm/amd/display/dc/dsc/Makefile | 4 +--- 5 files changed, 5 insertions(+), 15 deletions(-) (limited to 'drivers/gpu/drm/amd/display/dc/dcn20/Makefile') diff --git a/drivers/gpu/drm/amd/display/dc/calcs/Makefile b/drivers/gpu/drm/amd/display/dc/calcs/Makefile index a1af55a86508..26c6d735cdc7 100644 --- a/drivers/gpu/drm/amd/display/dc/calcs/Makefile +++ b/drivers/gpu/drm/amd/display/dc/calcs/Makefile @@ -37,9 +37,7 @@ ifdef IS_OLD_GCC # GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 # (8B stack alignment). calcs_ccflags += -mpreferred-stack-boundary=4 -endif - -ifdef CONFIG_CC_IS_CLANG +else calcs_ccflags += -msse2 endif diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/Makefile b/drivers/gpu/drm/amd/display/dc/dcn20/Makefile index cb0ac131f74a..63f3bddba7da 100644 --- a/drivers/gpu/drm/amd/display/dc/dcn20/Makefile +++ b/drivers/gpu/drm/amd/display/dc/dcn20/Makefile @@ -23,9 +23,7 @@ ifdef IS_OLD_GCC # GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 # (8B stack alignment). CFLAGS_$(AMDDALPATH)/dc/dcn20/dcn20_resource.o += -mpreferred-stack-boundary=4 -endif - -ifdef CONFIG_CC_IS_CLANG +else CFLAGS_$(AMDDALPATH)/dc/dcn20/dcn20_resource.o += -msse2 endif diff --git a/drivers/gpu/drm/amd/display/dc/dcn21/Makefile b/drivers/gpu/drm/amd/display/dc/dcn21/Makefile index f92320ddd27f..ff50ae71fe27 100644 --- a/drivers/gpu/drm/amd/display/dc/dcn21/Makefile +++ b/drivers/gpu/drm/amd/display/dc/dcn21/Makefile @@ -16,9 +16,7 @@ ifdef IS_OLD_GCC # GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 # (8B stack alignment). CFLAGS_$(AMDDALPATH)/dc/dcn21/dcn21_resource.o += -mpreferred-stack-boundary=4 -endif - -ifdef CONFIG_CC_IS_CLANG +else CFLAGS_$(AMDDALPATH)/dc/dcn21/dcn21_resource.o += -msse2 endif diff --git a/drivers/gpu/drm/amd/display/dc/dml/Makefile b/drivers/gpu/drm/amd/display/dc/dml/Makefile index ef1bdd20b425..8df251626e22 100644 --- a/drivers/gpu/drm/amd/display/dc/dml/Makefile +++ b/drivers/gpu/drm/amd/display/dc/dml/Makefile @@ -37,9 +37,7 @@ ifdef IS_OLD_GCC # GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 # (8B stack alignment). dml_ccflags += -mpreferred-stack-boundary=4 -endif - -ifdef CONFIG_CC_IS_CLANG +else dml_ccflags += -msse2 endif diff --git a/drivers/gpu/drm/amd/display/dc/dsc/Makefile b/drivers/gpu/drm/amd/display/dc/dsc/Makefile index 3f7840828a9f..970737217e53 100644 --- a/drivers/gpu/drm/amd/display/dc/dsc/Makefile +++ b/drivers/gpu/drm/amd/display/dc/dsc/Makefile @@ -14,9 +14,7 @@ ifdef IS_OLD_GCC # GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3 # (8B stack alignment). dsc_ccflags += -mpreferred-stack-boundary=4 -endif - -ifdef CONFIG_CC_IS_CLANG +else dsc_ccflags += -msse2 endif -- cgit v1.2.3