[PATCH] arm64: update compiler option for PAC

[Kuan-Ying Lee]

We pass -mbranch-protection=pac-ret+leaf to support PAC
when we use GCC 9 or later.

Before GCC 9, we pass -msign-return-address=all to support
PAC.

Signed-off-by: Kuan-Ying Lee <Kuan-Ying.Lee@xxxxxxxxxxxx>
---
 Documentation/arm64/pointer-authentication.rst | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/Documentation/arm64/pointer-authentication.rst b/Documentation/arm64/pointer-authentication.rst
index f127666ea3a8..055d08b0d42d 100644
--- a/Documentation/arm64/pointer-authentication.rst
+++ b/Documentation/arm64/pointer-authentication.rst
@@ -54,8 +54,10 @@ virtual address size configured by the kernel. For example, with a
 virtual address size of 48, the PAC is 7 bits wide.
 
 Recent versions of GCC can compile code with APIAKey-based return
-address protection when passed the -msign-return-address option. This
-uses instructions in the HINT space (unless -march=armv8.3-a or higher
+address protection when passed compiler option as following.
+Pass -msign-return-address when we use GCC 7, 8.
+Pass -mbranch-protection when we use GCC 9 or later.
+This uses instructions in the HINT space (unless -march=armv8.3-a or higher
 is also passed), and such code can run on systems without the pointer
 authentication extension.
 
-- 
2.18.0