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Date: Fri, 1 Jul 2022 15:41:08 +0100
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Subject: Re: [PATCH 6/12] arm: Add pointer authentication for stack-unwinding
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To: Andrea Corallo <andrea.corallo@arm.com>,
 Andrea Corallo via Gcc-patches <gcc-patches@gcc.gnu.org>
Cc: Richard Earnshaw <Richard.Earnshaw@arm.com>, nd <nd@arm.com>
References: <gkrmtg5wqik.fsf@arm.com> <gkrwnf9v8yi.fsf@arm.com>
From: Richard Earnshaw <Richard.Earnshaw@foss.arm.com>
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On 28/04/2022 10:44, Andrea Corallo via Gcc-patches wrote:
> This patch adds authentication for when the stack is unwound when an
> exception is taken.  All the changes here are done to the runtime code
> in libgcc's unwinder code for Arm target. All the changes are guarded
> under defined (__ARM_FEATURE_PAC_DEFAULT) and activated only if the
> +pacbti feature is switched on for the architecture. This means that
> switching on the target feature via -march or -mcpu is sufficient and
> -mbranch-protection need not be enabled. This ensures that the
> unwinder is authenticated only if the PACBTI instructions are
> available in the non-NOP space as it uses AUTG.  Just generating
> PAC/AUT instructions using -mbranch-protection will not enable
> authentication on the unwinder.
> 
> Pre-approved with the requested changes here
> <https://gcc.gnu.org/pipermail/gcc-patches/2021-December/586555.html>.
> 
> gcc/ChangeLog:
> 
> 	* ginclude/unwind-arm-common.h (_Unwind_VRS_RegClass): Introduce
> 	new pseudo register class _UVRSC_PAC.
> 	* libgcc/config/arm/pr-support.c (__gnu_unwind_execute): Decode
> 	exception opcode (0xb4) for saving RA_AUTH_CODE and authenticate
> 	with AUTG if found.
> 	* libgcc/config/arm/unwind-arm.c (struct pseudo_regs): New.
> 	(phase1_vrs): Introduce new field to store pseudo-reg state.
> 	(phase2_vrs): Likewise.
> 	(_Unwind_VRS_Get): Load pseudo register state from virtual reg set.
> 	(_Unwind_VRS_Set): Store pseudo register state to virtual reg set.
> 	(_Unwind_VRS_Pop): Load pseudo register value from stack into VRS.
> 
> Co-Authored-By: Tejas Belagod  <tbelagod@arm.com>
> 

Ok.

R.