[PATCH 5.6 72/73] arm64: vdso: Add -fasynchronous-unwind-tables to cflags

[Greg Kroah-Hartman]

From: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>

commit 1578e5d03112e3e9d37e1c4d95b6dfb734c73955 upstream.

On arm64 linux gcc uses -fasynchronous-unwind-tables -funwind-tables
by default since gcc-8, so now the de facto platform ABI is to allow
unwinding from async signal handlers.

However on bare metal targets (aarch64-none-elf), and on old gcc,
async and sync unwind tables are not enabled by default to avoid
runtime memory costs.

This means if linux is built with a baremetal toolchain the vdso.so
may not have unwind tables which breaks the gcc platform ABI guarantee
in userspace.

Add -fasynchronous-unwind-tables explicitly to the vgettimeofday.o
cflags to address the ABI change.

Fixes: 28b1a824a4f4 ("arm64: vdso: Substitute gettimeofday() with C implementation")
Cc: Will Deacon <will@xxxxxxxxxx>
Reported-by: Szabolcs Nagy <szabolcs.nagy@xxxxxxx>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/arm64/kernel/vdso/Makefile |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -32,7 +32,7 @@ UBSAN_SANITIZE			:= n
 OBJECT_FILES_NON_STANDARD	:= y
 KCOV_INSTRUMENT			:= n
 
-CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny
+CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny -fasynchronous-unwind-tables
 
 ifneq ($(c-gettimeofday-y),)
   CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)