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Date:   Fri, 18 Feb 2022 14:12:40 -0800
From:   Joao Moreira <joao@overdrivepizza.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     x86@kernel.org, hjl.tools@gmail.com, jpoimboe@redhat.com,
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        samitolvanen@google.com, mark.rutland@arm.com,
        alyssa.milburn@intel.com
Subject: Re: [PATCH 05/29] x86: Base IBT bits
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 <20220218171408.867389898@infradead.org>
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> +config CC_HAS_IBT
> +	# GCC >= 9 and binutils >= 2.29
> +	# Retpoline check to work around
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93654
> +	def_bool $(cc-option, -fcf-protection=branch
> -mindirect-branch-register) && $(as-instr,endbr64)
> +
Is -mindirect-branch-register breaks compiling with clang. Maybe we 
should we do instead?

+       def_bool ($(cc-option, -fcf-protection=branch 
-mindirect-branch-register) || $(cc-option, -mretpoline-external-thunk)) 
&& $(as-instr,endbr64)