linux-kernel - Re: [PATCH v6 01/10] x86/retpoline: Add initial retpoline support

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Date:   Mon, 8 Jan 2018 12:03:09 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Andi Kleen <ak@...ux.intel.com>, Paul Turner <pjt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCH v6 01/10] x86/retpoline: Add initial retpoline support

On Mon, Jan 08, 2018 at 10:53:02AM +0000, David Woodhouse wrote:
> On Mon, 2018-01-08 at 11:45 +0100, Peter Zijlstra wrote:
> > 
> > 
> > Should this not use local name labels instead?
> > 
> > .macro RETPOLINE_JMP reg:req
> >         call    .Ldo_rop_\@
> > .Lspec_trap_\@:
> >         pause
> >         jmp .Lspec_trap_\@
> > .Ldo_rop_\@:
> >         mov     \reg, (%_ASM_SP)
> >         ret
> > .endm
> 
> Not if you want to be able to use them twice in the same .S file.

Should work fine, the \@ expands to a per-instance magic thing IIRC. All
the PTI helpers do this too and that works just fine, see
arch/x86/entry/calling.h