Hello,

This patch teaches the DWARF support in gcc about RA_AUTH_CODE pseudo hard-register and also 
updates the ".save", ".cfi_register", ".cfi_offset", ".cfi_restore" directives accordingly.
This patch also adds support to emit ".pacspval" directive when "pac ip, lr, sp" instruction
in generated in the assembly.

RA_AUTH_CODE register number is 107 and it's dwarf register number is 143.

Applying this patch on top of PACBTI series posted here
https://gcc.gnu.org/pipermail/gcc-patches/2022-August/599658.html and when compiling the following
test.c with "-march=armv8.1-m.main+mve+pacbti -mbranch-protection=pac-ret -mthumb -mfloat-abi=hard
fasynchronous-unwind-tables -g -O0 -S" command line options, the assembly output after this patch
looks like below:

$cat test.c

void fun1(int a);
void fun(int a,...)
{
  fun1(a);
}

int main()
{
  fun (10);
  return 0;
}

$ arm-none-eabi-gcc -march=armv8.1-m.main+mve+pacbti -mbranch-protection=pac-ret -mthumb -mfloat-abi=hard
-fasynchronous-unwind-tables -g -O0 -S test.s

Assembly output:
...
fun:
...
        .pacspval
        pac     ip, lr, sp
        .cfi_register 143, 12
        push    {r3, r7, ip, lr}
        .save {r3, r7, ra_auth_code, lr}
...
        .cfi_offset 143, -24
...
        .cfi_restore 143
...
        aut     ip, lr, sp
        bx      lr
...
main:
...
        .pacspval
        pac     ip, lr, sp
        .cfi_register 143, 12
        push    {r3, r7, ip, lr}
        .save {r3, r7, ra_auth_code, lr}
...
        .cfi_offset 143, -8
...
        .cfi_restore 143
...
        aut     ip, lr, sp
        bx      lr
...

Regression tested on arm-none-eabi target and found no regressions.

Ok for master?

Regards,
Srinath.

2023-01-18  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>

        * config/arm/aout.h (ra_auth_code): Add entry in enum.
        (emit_multi_reg_push): Add RA_AUTH_CODE register to
        dwarf frame expression.
        (arm_emit_multi_reg_pop): Restore RA_AUTH_CODE register.
        (arm_expand_prologue): Update frame related information and reg notes
        for pac/pacbit insn.
        (arm_regno_class): Check for pac pseudo reigster.
        (arm_dbx_register_number): Assign ra_auth_code register number in dwarf.
        (arm_init_machine_status): Set pacspval_needed to zero.
        (arm_debugger_regno): Check for PAC register.
        (arm_unwind_emit_sequence): Print .save directive with ra_auth_code
        register.
        (arm_unwind_emit_set): Add entry for IP_REGNUM in switch case.
        (arm_unwind_emit): Update REG_CFA_REGISTER case._
        * config/arm/arm.h (FIRST_PSEUDO_REGISTER): Modify.
        (DWARF_PAC_REGNUM): Define.
        (IS_PAC_REGNUM): Likewise.
        (enum reg_class): Add PAC_REG entry.
        (machine_function): Add pacbti_needed state to structure.
        * config/arm/arm.md (RA_AUTH_CODE): Define.

gcc/testsuite/ChangeLog:

2023-01-18  Srinath Parvathaneni  <srinath.parvathaneni@arm.com>

        * g++.target/arm/pac-1.C: New test.
        * gcc.target/arm/pac-15.c: Likewise.