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

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Date:   Mon, 12 Feb 2018 15:59:24 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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, Feb 12, 2018 at 12:57:40PM +0000, David Woodhouse wrote:
> 
> 
> 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? 

I couldn't make it work there, but it could be my makefile foo isn't
strong enough. The ordering of arch/*/Makefile vs scripts/Makefile.build
is forever confusing me.