[PATCH v2][GCC] arm: Add support for new frame unwinding instruction "0xb5".

[Srinath Parvathaneni via Gcc-patches]

Hi,

This patch adds support for Arm frame unwinding instruction "0xb5" [1]. When
an exception is taken and "0xb5" instruction is encounter during runtime
stack-unwinding, we use effective vsp as modifier in pointer authentication.
On completion of stack unwinding if "0xb5" instruction is not encountered
then CFA will be used as modifier in pointer authentication.

[1] https://github.com/ARM-software/abi-aa/releases/download/2022Q3/ehabi32.pdf

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

Ok for master?

Regards,
Srinath.

gcc/ChangeLog:

2022-11-09  Srinath Parvathaneni  <srinath.parvathan...@arm.com>

        * libgcc/config/arm/pr-support.c (__gnu_unwind_execute): Decode opcode 
"0xb5".


###############     Attachment also inlined for ease of reply    ###############


diff --git a/libgcc/config/arm/pr-support.c b/libgcc/config/arm/pr-support.c
index 
e48854587c667a959aa66ccc4982231f63333ecc..1fbc41e17c227c21af1937344ded2a7fd80e61df
 100644
--- a/libgcc/config/arm/pr-support.c
+++ b/libgcc/config/arm/pr-support.c
@@ -107,7 +107,9 @@ __gnu_unwind_execute (_Unwind_Context * context, 
__gnu_unwind_state * uws)
   _uw op;
   int set_pc;
   int set_pac = 0;
+  int set_pac_sp = 0;
   _uw reg;
+  _uw sp;
 
   set_pc = 0;
   for (;;)
@@ -124,10 +126,11 @@ __gnu_unwind_execute (_Unwind_Context * context, 
__gnu_unwind_state * uws)
 #if defined(TARGET_HAVE_PACBTI)
          if (set_pac)
            {
-             _uw sp;
              _uw lr;
              _uw pac;
-             _Unwind_VRS_Get (context, _UVRSC_CORE, R_SP, _UVRSD_UINT32, &sp);
+             if (!set_pac_sp)
+               _Unwind_VRS_Get (context, _UVRSC_CORE, R_SP, _UVRSD_UINT32,
+                                &sp);
              _Unwind_VRS_Get (context, _UVRSC_CORE, R_LR, _UVRSD_UINT32, &lr);
              _Unwind_VRS_Get (context, _UVRSC_PAC, R_IP,
                               _UVRSD_UINT32, &pac);
@@ -259,6 +262,14 @@ __gnu_unwind_execute (_Unwind_Context * context, 
__gnu_unwind_state * uws)
              continue;
            }
 
+         /* Use current VSP as modifier in PAC validation.  */
+         if (op == 0xb5)
+           {
+             _Unwind_VRS_Get (context, _UVRSC_CORE, R_SP, _UVRSD_UINT32, &sp);
+             set_pac_sp = 1;
+             continue;
+           }
+
          if ((op & 0xfc) == 0xb4)  /* Obsolete FPA.  */
            return _URC_FAILURE;
 




diff --git a/libgcc/config/arm/pr-support.c b/libgcc/config/arm/pr-support.c
index 
e48854587c667a959aa66ccc4982231f63333ecc..1fbc41e17c227c21af1937344ded2a7fd80e61df
 100644
--- a/libgcc/config/arm/pr-support.c
+++ b/libgcc/config/arm/pr-support.c
@@ -107,7 +107,9 @@ __gnu_unwind_execute (_Unwind_Context * context, 
__gnu_unwind_state * uws)
   _uw op;
   int set_pc;
   int set_pac = 0;
+  int set_pac_sp = 0;
   _uw reg;
+  _uw sp;
 
   set_pc = 0;
   for (;;)
@@ -124,10 +126,11 @@ __gnu_unwind_execute (_Unwind_Context * context, 
__gnu_unwind_state * uws)
 #if defined(TARGET_HAVE_PACBTI)
          if (set_pac)
            {
-             _uw sp;
              _uw lr;
              _uw pac;
-             _Unwind_VRS_Get (context, _UVRSC_CORE, R_SP, _UVRSD_UINT32, &sp);
+             if (!set_pac_sp)
+               _Unwind_VRS_Get (context, _UVRSC_CORE, R_SP, _UVRSD_UINT32,
+                                &sp);
              _Unwind_VRS_Get (context, _UVRSC_CORE, R_LR, _UVRSD_UINT32, &lr);
              _Unwind_VRS_Get (context, _UVRSC_PAC, R_IP,
                               _UVRSD_UINT32, &pac);
@@ -259,6 +262,14 @@ __gnu_unwind_execute (_Unwind_Context * context, 
__gnu_unwind_state * uws)
              continue;
            }
 
+         /* Use current VSP as modifier in PAC validation.  */
+         if (op == 0xb5)
+           {
+             _Unwind_VRS_Get (context, _UVRSC_CORE, R_SP, _UVRSD_UINT32, &sp);
+             set_pac_sp = 1;
+             continue;
+           }
+
          if ((op & 0xfc) == 0xb4)  /* Obsolete FPA.  */
            return _URC_FAILURE;