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

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Date:   Thu, 07 Mar 2019 09:19:04 -0800
From:   Joe Perches <joe@...ches.com>
To:     Arnd Bergmann <arnd@...db.de>,
        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>
Cc:     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, 2019-03-07 at 10:14 +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.

Perhaps the __init and __exit #defines should be noinline
to allow discarding of the code.

These defines are already marked with __section so I'd've
expected these to be noinline anyway.

---
 include/linux/init.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/init.h b/include/linux/init.h
index 5255069f5a9f..806215a74064 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -47,7 +47,7 @@
 
 /* These are for everybody (although not all archs will actually
    discard it in modules) */
-#define __init		__section(.init.text) __cold  __latent_entropy __noinitretpoline
+#define __init		__section(.init.text) __cold  __latent_entropy __noinitretpoline noinline
 #define __initdata	__section(.init.data)
 #define __initconst	__section(.init.rodata)
 #define __exitdata	__section(.exit.data)
@@ -80,7 +80,7 @@
 #define __exitused  __used
 #endif
 
-#define __exit          __section(.exit.text) __exitused __cold notrace
+#define __exit          __section(.exit.text) __exitused __cold notrace noinline
 
 /* Used for MEMORY_HOTPLUG */
 #define __meminit        __section(.meminit.text) __cold notrace \