[PATCH] arm64: support __int128 on gcc 5+

[Jason A. Donenfeld]

Versions of gcc prior to gcc 5 emitted a __multi3 function call when
dealing with TI types, resulting in failures when trying to link to
libgcc, and more generally, horrible performance. However, since gcc 5,
the compiler supports actually emitting fast instructions, which means
we can at long last enable this option and receive the speedups.

The gcc commit that added proper Aarch64 support is:
https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=d1ae7bb994f49316f6f63e6173f2931e837a351d

This commit appears to be part of the gcc 5 release.

Signed-off-by: Jason A. Donenfeld <Jason at zx2c4.com>
---
 arch/arm64/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index 939b310913cf..1f8a0fec6998 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -53,6 +53,8 @@ KBUILD_AFLAGS	+= $(lseinstr) $(brokengasinst)
 KBUILD_CFLAGS	+= $(call cc-option,-mabi=lp64)
 KBUILD_AFLAGS	+= $(call cc-option,-mabi=lp64)
 
+KBUILD_CFLAGS	+= $(call cc-ifversion, -ge, 0500, -DCONFIG_ARCH_SUPPORTS_INT128)
+
 ifeq ($(CONFIG_CPU_BIG_ENDIAN), y)
 KBUILD_CPPFLAGS	+= -mbig-endian
 CHECKFLAGS	+= -D__AARCH64EB__
-- 
2.14.2