linux-kernel - Re: [PATCH v2 08/59] x86/build: Ensure proper function alignment

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Message-ID: <YxI+K8Y+f/FHSQCU@hirez.programming.kicks-ass.net>
Date:   Fri, 2 Sep 2022 19:32:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org, Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v2 08/59] x86/build: Ensure proper function alignment

On Fri, Sep 02, 2022 at 09:51:17AM -0700, Linus Torvalds wrote:
> On Fri, Sep 2, 2022 at 6:55 AM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > --- a/arch/x86/include/asm/linkage.h
> > +++ b/arch/x86/include/asm/linkage.h
> > @@ -14,9 +14,10 @@
> >
> >  #ifdef __ASSEMBLY__
> >
> > -#if defined(CONFIG_X86_64) || defined(CONFIG_X86_ALIGNMENT_16)
> > -#define __ALIGN                .p2align 4, 0x90
> > -#define __ALIGN_STR    __stringify(__ALIGN)
> > +#if CONFIG_FUNCTION_ALIGNMENT == 16
> > +#define __ALIGN                        .p2align 4, 0x90
> > +#define __ALIGN_STR            __stringify(__ALIGN)
> > +#define FUNCTION_ALIGNMENT     16
> >  #endif
> 
> Ugh.
> 
> Why is this conditional on that alignment being 16?

There is a DEBUG case that increases the thing to 32.