[PATCH 2/15] arm: Add Armv8.1-M Mainline target feature +pacbti

This patch adds the -march feature +pacbti to Armv8.1-M Mainline.
This feature enables pointer signing and authentication instructions
on M-class architectures.

Pre-approved here
<https://gcc.gnu.org/pipermail/gcc-patches/2021-December/586144.html>.

gcc/Changelog:

	* config/arm/arm.h (TARGET_HAVE_PACBTI): New macro.
	* config/arm/arm-cpus.in (pacbti): New feature.
	* doc/invoke.texi (Arm Options): Document it.

Co-Authored-By: Tejas Belagod  <tbelagod@arm.com>

gcc/config/arm/arm-cpus.in

@@ -229,6 +229,10 @@ define feature cdecp5
 define feature cdecp6
 define feature cdecp7
 
+# M-profile control flow integrity extensions (PAC/AUT/BTI).
+# Optional from Armv8.1-M Mainline.
+define feature pacbti
+
 # Feature groups.  Conventionally all (or mostly) upper case.
 # ALL_FPU lists all the feature bits associated with the floating-point
 # unit; these will all be removed if the floating-point unit is disabled
@@ -743,6 +747,7 @@ begin arch armv8.1-m.main
  isa ARMv8_1m_main
 # fp => FPv5-sp-d16; fp.dp => FPv5-d16
  option dsp add armv7em
+ option pacbti add pacbti
  option fp add FPv5 fp16
  option fp.dp add FPv5 FP_DBL fp16
  option nofp remove ALL_FP

gcc/config/arm/arm.h

@@ -331,6 +331,12 @@ emission of floating point pcs attributes.  */
 						isa_bit_mve_float) \
 			       && !TARGET_GENERAL_REGS_ONLY)
 
+/* Non-zero if this target supports Armv8.1-M Mainline pointer-signing
+   extension.  */
+#define TARGET_HAVE_PACBTI (arm_arch8_1m_main \
+			    && bitmap_bit_p (arm_active_target.isa, \
+					     isa_bit_pacbti))
+
 /* MVE have few common instructions as VFP, like VLDM alias VPOP, VLDR, VSTM
    alia VPUSH, VSTR and VMOV, VMSR and VMRS.  In the same manner it updates few
    registers such as FPCAR, FPCCR, FPDSCR, FPSCR, MVFR0, MVFR1 and MVFR2.  All

gcc/doc/invoke.texi

@@ -22020,6 +22020,9 @@ Disable the floating-point extension.
 @item +cdecp0, +cdecp1, ... , +cdecp7
 Enable the Custom Datapath Extension (CDE) on selected coprocessors according
 to the numbers given in the options in the range 0 to 7.
+
+@item +pacbti
+Enable the Pointer Authentication and Branch Target Identification Extension.
 @end table
 
 @item  armv8-m.main