linux-kernel - Re: [PATCH 1/2] futex: mark futex_detect

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Date:   Thu, 7 Mar 2019 10:12:11 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Russell King <linux@...linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] futex: mark futex_detect_cmpxchg() as 'noinline'

On Thu, Mar 7, 2019 at 1:15 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On 32-bit ARM, I got a link failure in futex_init() when building
> with clang in some random configurations:
>
> kernel/futex.o:(.text.fixup+0x5c): relocation truncated to fit: R_ARM_JUMP24 against `.init.text'

Do we know what function from the fixup text section is calling
futex_detect_cmpxchg?  I'm curious if this is maybe another case of
-Wsection where some function may be in the wrong section?

>
> As far as I can tell, the problem is that a branch is over 16MB
> apart in those configurations, but only if it branches back to
> the init text.
>
> Marking the futex_detect_cmpxchg() function as noinline and
> not __init avoids the problem for me.
>
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  kernel/futex.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/futex.c b/kernel/futex.c
> index c3b73b0311bc..dda77ed9f445 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -3849,7 +3849,7 @@ SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
>  }
>  #endif /* CONFIG_COMPAT_32BIT_TIME */
>
> -static void __init futex_detect_cmpxchg(void)
> +static noinline void futex_detect_cmpxchg(void)
>  {
>  #ifndef CONFIG_HAVE_FUTEX_CMPXCHG
>         u32 curval;
> --
> 2.20.0
>


-- 
Thanks,
~Nick Desaulniers