linux-kernel - Re: [PATCH v2 4/8] objtool: Retpoline validation tweaks

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Message-ID: <1518440260.6606.58.camel@infradead.org>
Date:   Mon, 12 Feb 2018 12:57:40 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>
Subject: Re: [PATCH v2 4/8] objtool: Retpoline validation tweaks



On Mon, 2018-02-12 at 13:48 +0100, Peter Zijlstra wrote:
> --- a/Makefile
> +++ b/Makefile
> @@ -486,6 +486,11 @@ KBUILD_CFLAGS += $(CLANG_TARGET) $(CLANG
>  KBUILD_AFLAGS += $(CLANG_TARGET) $(CLANG_GCC_TC)
>  endif
>  
> +ifneq ($(call cc-option,-mindirect-branch=thunk-extern -mindirect-branch-register),)
> +  CC_HAS_RETPOLINE := 1
> +endif
> +export CC_HAS_RETPOLINE

Can't you do that with the existing check in arch/x86/Makefile? 

cf. http://git.infradead.org/users/dwmw2/linux-retpoline.git/commitdiff/eb12299ed
which is going nowhere until https://bugs.llvm.org/show_bug.cgi?id=36329
gets fixed but still I'd like to have the check in *one* place.
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