linux-kernel - Re: [PATCH] fs/select: mark do_select noinline_for

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Date:   Mon, 10 Oct 2022 21:55:47 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>
Cc:     "Alexander Viro" <viro@...iv.linux.org.uk>,
        "Nathan Chancellor" <nathan@...nel.org>,
        "Tom Rix" <trix@...hat.com>, "Xiaoming Ni" <nixiaoming@...wei.com>,
        "Luis Chamberlain" <mcgrof@...nel.org>,
        "Andi Kleen" <ak@...ux.intel.com>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        "Christoph Hellwig" <hch@....de>,
        "Eric Dumazet" <edumazet@...gle.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] fs/select: mark do_select noinline_for_stack for 32b

On Fri, Oct 7, 2022, at 10:11 PM, Nick Desaulniers wrote:
> +#ifdef CONFIG_64BIT
> +#define noinline_for_stack_32b
> +#else
> +#define noinline_for_stack_32b noinline_for_stack
> +#endif
> +
> +noinline_for_stack_32b

I don't see much value in making it behave differently for 32 bit:
it doesn't reduce the total frame size on 32-bit machines but only
hides the warning. The bug you are working around also looks i386
specific (because of limited number of registers vs ubsan needing
a lot of them), so just make it a simple 'noinline_for_stack'.

      Arnd