linux-kernel - Re: [tip:x86/build] x86/build: Remove -Wno-sign-compare

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Date:	Tue, 12 May 2015 13:51:42 -0400
From:	Waiman Long <waiman.long@...com>
To:	Ingo Molnar <mingo@...nel.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Peter Anvin <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...capital.net>,
	Louis Langholtz <lou_langholtz@...com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [tip:x86/build] x86/build: Remove -Wno-sign-compare

On 05/12/2015 04:53 AM, Ingo Molnar wrote:
> * Ingo Molnar<mingo@...nel.org>  wrote:
>
>> Here's the full list of warnings for allmod64:
>>
>> make bzImage:
>>
>>   include/linux/blkdev.h:624:26: warning: switch condition has boolean value [-Wswitch-bool]
>>   ./arch/x86/include/asm/qspinlock.h:28:2: warning: implicit declaration of function ?pv_queued_spin_lock_slowpath? [-Wimplicit-function-declaration]
>>   ./arch/x86/include/asm/qspinlock.h:33:2: warning: implicit declaration of function ?pv_queued_spin_unlock? [-Wimplicit-function-declaration]
>>   ./arch/x86/include/asm/qspinlock.h:28:2: warning: implicit declaration of function ?pv_queued_spin_lock_slowpath? [-Wimplicit-function-declaration]
>>   ./arch/x86/include/asm/qspinlock.h:33:2: warning: implicit declaration of function ?pv_queued_spin_unlock? [-Wimplicit-function-declaration]
>>   ./arch/x86/include/asm/qspinlock.h:28:2: warning: implicit declaration of function ?pv_queued_spin_lock_slowpath? [-Wimplicit-function-declaration]
>>   ./arch/x86/include/asm/qspinlock.h:33:2: warning: implicit declaration of function ?pv_queued_spin_unlock? [-Wimplicit-function-declaration]
>>   ./arch/x86/include/asm/qspinlock.h:28:2: warning: implicit declaration of function ?pv_queued_spin_lock_slowpath? [-Wimplicit-function-declaration]
>>   ./arch/x86/include/asm/qspinlock.h:33:2: warning: implicit declaration of function ?pv_queued_spin_unlock? [-Wimplicit-function-declaration]
> And that comes from tip:locking/core, but those warnings do not show
> up with GCC 4.9.2: so it's either a GCC 5.0.1 bug, or we missed
> something with the WIP queued pv spinlocks changes that newer GCC is
> able to notice.
>
> Thanks,
>
> 	Ingo

The only way this can happen is when __ASSEMBLY__ is defined and 
asm/qspinlock.h is included. Could you apply the following patch to see 
if it can fix the compilation warnings? I don't have a gcc 5 compiler on 
hand to verify that.

Cheers,
Longman


---
  arch/x86/include/asm/qspinlock.h |    5 ++++-
  1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/qspinlock.h 
b/arch/x86/include/asm/qspinlock.h
index 9d51fae..3ea1c57 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -17,7 +17,10 @@ static inline void native_queued_spin_unlock(struct 
qspinlock *lock)
      smp_store_release((u8 *)lock, 0);
  }

-#ifdef CONFIG_PARAVIRT_SPINLOCKS
+/*
+ * Disable the PV code for assembly to prevent compilation warnings.
+ */
+#if defined(CONFIG_PARAVIRT_SPINLOCKS) && !defined(__ASSEMBLY__)
  extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, 
u32 val);
  extern void __pv_init_lock_hash(void);
  extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 
val);
-- 


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