linux-kernel - Re: [RFC 1/4] asm-generic/uaccess: don't define inline functions if noinline lib/* in use

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Date:   Tue, 14 Jan 2020 21:57:42 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:     Khalid Aziz <khalid.aziz@...cle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "open list:SYNOPSYS ARC ARCHITECTURE" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [RFC 1/4] asm-generic/uaccess: don't define inline functions if
 noinline lib/* in use

On Tue, Jan 14, 2020 at 9:08 PM Vineet Gupta <Vineet.Gupta1@...opsys.com> wrote:
>
> There are 2 generic varaints of strncpy_from_user() / strnlen_user()
>  (1). inline version in asm-generic/uaccess.h
>  (2). optimized word-at-a-time version in lib/*
>
> This patch disables #1 if #2 selected. This allows arches to continue
> reusing asm-generic/uaccess.h for rest of code
>
> This came up when switching ARC to generic word-at-a-time interface
>
> Signed-off-by: Vineet Gupta <vgupta@...opsys.com>

This looks like a useful change, but I think we can do even better: It
seems that
there are no  callers of __strnlen_user or __strncpy_from_user  in the
kernel today, so these should not be defined either when the Kconfig symbols
are set. Also, I would suggest moving the 'extern' declaration for the two
functions into the #else branch of the conditional so it does not need to be
duplicated.

      Arnd