linux-kernel - Re: [PATCH 02/17] x86, lto: Mark all top level asm statements as .text

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Message-ID: <20190327204049.GW18020@tassilo.jf.intel.com>
Date:   Wed, 27 Mar 2019 13:40:49 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 02/17] x86, lto: Mark all top level asm statements as
 .text

> +     asm(".pushsection .rodata, \"a\"\n"                             \                                                
> +         NATIVE_LABEL("start_", ops, name)                           \                                                
> +         code                                                        \                                                
> +         NATIVE_LABEL("end_", ops, name)                             \                                                
> +         ".popsection\n")                                                            

> 
> It's static so it's scope is within the file and whatever GCC does with
> that C function it has to respect that it accesses static data. If that's
> not true then this really needs to be fixed at the compiler side and not in
> the kernel.

Ok so you did the statics with undefined size, so kind of an extern static. 
That's a weird construct (not sure if it's even allowed in standard C), but
somehow it seems to work in gcc with the inline assembler.

I checked the code general and with the .globl in NATIVE_LABEL the 
generated assembler looks like it should work even for LTO yes.

I guess it's an interesting alternative to making them all global.
Maybe that will work for more cases too.

Thanks.

-Andi