[RFC PATCH v3 08/31] KVM: selftests: Require GCC to realign stacks on function entry

[Ackerley Tng]

Some SSE instructions assume a 16-byte aligned stack, and GCC compiles
assuming the stack is aligned:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40838. This combination
results in a #GP in guests.

Adding this compiler flag will generate an alternate prologue and
epilogue to realign the runtime stack, which makes selftest code
slower and bigger, but this is okay since we do not need selftest code
to be extremely performant.

Similar issue discussed at
https://lore.kernel.org/all/CAGtprH9yKvuaF5yruh3BupQe4BxDGiBQk3ExtY2m39yP-tppsg@xxxxxxxxxxxxxx/

Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
---
 tools/testing/selftests/kvm/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
index 317927d9c55bd..5f9cc1e6ee67e 100644
--- a/tools/testing/selftests/kvm/Makefile
+++ b/tools/testing/selftests/kvm/Makefile
@@ -205,7 +205,7 @@ LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/x86/include
 else
 LINUX_TOOL_ARCH_INCLUDE = $(top_srcdir)/tools/arch/$(ARCH)/include
 endif
-CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
+CFLAGS += -mstackrealign -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \
 	-fno-stack-protector -fno-PIE -I$(LINUX_TOOL_INCLUDE) \
 	-I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \
 	-I$(<D) -Iinclude/$(UNAME_M) -I ../rseq -I.. $(EXTRA_CFLAGS) \
-- 
2.39.0.246.g2a6d74b583-goog