[PATCH 2/5] aarch64: Add support for GCS system registers with the +gcs modifier

[Victor Do Nascimento <victor.donascimento@arm.com>]

Given the introduction of system registers associated with the Guarded
Control Stack extension to Armv9.4-a in Binutils and their reliance on
the `+gcs' modifier, we implement the necessary changes in GCC to
allow for them to be recognized by the compiler.

gcc/ChangeLog:

	* config/aarch64/aarch64-option-extensions.def (gcs): New.
	* config/aarch64/aarch64.h (AARCH64_ISA_GCS): New.
	(TARGET_THE):  Likewise.
	* doc/invoke.texi (AArch64 Options): Describe GCS.
---
 gcc/config/aarch64/aarch64-option-extensions.def | 2 ++
 gcc/config/aarch64/aarch64.h                     | 6 ++++++
 gcc/doc/invoke.texi                              | 2 ++
 3 files changed, 10 insertions(+)

diff --git a/gcc/config/aarch64/aarch64-option-extensions.def b/gcc/config/aarch64/aarch64-option-extensions.def
index da31f7c32d1..e72c039b612 100644
--- a/gcc/config/aarch64/aarch64-option-extensions.def
+++ b/gcc/config/aarch64/aarch64-option-extensions.def
@@ -155,4 +155,6 @@ AARCH64_OPT_EXTENSION("d128", D128, (), (), (), "d128")
 
 AARCH64_OPT_EXTENSION("the", THE, (), (), (), "the")
 
+AARCH64_OPT_EXTENSION("gcs", GCS, (), (), (), "gcs")
+
 #undef AARCH64_OPT_EXTENSION
diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
index 1b3c800ec89..69ef54553d7 100644
--- a/gcc/config/aarch64/aarch64.h
+++ b/gcc/config/aarch64/aarch64.h
@@ -230,6 +230,7 @@ enum class aarch64_feature : unsigned char {
 #define AARCH64_ISA_CSSC	   (aarch64_isa_flags & AARCH64_FL_CSSC)
 #define AARCH64_ISA_D128	   (aarch64_isa_flags & AARCH64_FL_D128)
 #define AARCH64_ISA_THE		   (aarch64_isa_flags & AARCH64_FL_THE)
+#define AARCH64_ISA_GCS		   (aarch64_isa_flags & AARCH64_FL_GCS)
 
 /* AARCH64_FL options necessary for system register implementation.  */
 
@@ -403,6 +404,11 @@ enum class aarch64_feature : unsigned char {
     enabled through +the.  */
 #define TARGET_THE (AARCH64_ISA_THE)
 
+/*  Armv9.4-A Guarded Control Stack extension system registers are
+    enabled through +gcs.  */
+#define TARGET_GCS (AARCH64_ISA_GCS)
+
+
 /* Standard register usage.  */
 
 /* 31 64-bit general purpose registers R0-R30:
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 88327ce9681..88ee1fdb524 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -21032,6 +21032,8 @@ Enable the Pointer Authentication Extension.
 Enable the Common Short Sequence Compression instructions.
 @item d128
 Enable support for 128-bit system register read/write instructions.
+@item gcs
+Enable support for Armv9.4-a Guarded Control Stack extension.
 @item the
 Enable support for Armv8.9-a/9.4-a translation hardening extension.
 
-- 
2.41.0