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authorNick Desaulniers <ndesaulniers@google.com>2019-10-16 16:02:08 -0700
committerAlex Deucher <alexander.deucher@amd.com>2019-10-30 11:56:20 -0400
commit00db297106e81770e7c4319014a67896053b5a22 (patch)
tree1327f93bc836bb0a9e04f50468ab5b494cb542a5 /drivers/gpu/drm/amd/display/dc/dcn21
parentc868868f6b6a5272350781f9a19b3a5ba1c00b02 (diff)
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 <ndesaulniers@google.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Diffstat (limited to 'drivers/gpu/drm/amd/display/dc/dcn21')
-rw-r--r--drivers/gpu/drm/amd/display/dc/dcn21/Makefile9
1 files changed, 9 insertions, 0 deletions
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