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

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Date:   Sat, 12 Dec 2020 13:26:25 +0100
From:   Marco Elver <elver@...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>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] futex: mark futex_detect_cmpxchg() as 'noinline'

On Thu, Mar 07, 2019 at 10:14AM +0100, Arnd Bergmann 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'
> 
> 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;

What ever happened to this patch?

I'm seeing this again with the attached config + next-20201211 (for
testing https://bugs.llvm.org/show_bug.cgi?id=48492). Had to apply this
patch to build the kernel.

Thanks,
-- Marco

View attachment ".config" of type "text/plain" (241263 bytes)