linux-kernel - Re: [PATCH] locking/qspinlock: Fix build for anonymous union in older gcc compilers

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Date:   Fri, 22 Jun 2018 10:05:08 +0800
From:   Waiman Long <longman@...hat.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Will Deacon <will.deacon@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] locking/qspinlock: Fix build for anonymous union in older
 gcc compilers

On 06/22/2018 08:35 AM, Steven Rostedt wrote:
> From: Steven Rostedt (VMware) <rostedt@...dmis.org>
>
> One of my tests compiles the kernel with gcc 4.5.3, and I hit the
> following build error:
>
> /work/git/linux-trace.git/include/linux/semaphore.h: In function 'sema_init':
> /work/git/linux-trace.git/include/linux/semaphore.h:35:17: error: unknown field 'val' specified in initializer
> /work/git/linux-trace.git/include/linux/semaphore.h:35:17: warning: missing braces around initializer
> /work/git/linux-trace.git/include/linux/semaphore.h:35:17: warning: (near initialization for '(anonymous).raw_lock.<anonymous>.val')
> In file included from /work/git/linux-trace.git/include/linux/sched/user.h:7:0,
>                  from /work/git/linux-trace.git/include/linux/cred.h:22,
>                  from /work/git/linux-trace.git/include/linux/seq_file.h:12,
>                  from /work/git/linux-trace.git/include/linux/cgroup.h:18,
>                  from /work/git/linux-trace.git/include/linux/memcontrol.h:22,
>                  from /work/git/linux-trace.git/include/linux/swap.h:9,
>                  from /work/git/linux-trace.git/include/linux/suspend.h:5,
>                  from /work/git/linux-trace.git/arch/x86/kernel/asm-offsets.c:13:
>
>
> I bisected it down to the introduction of the commit that makes
> qspinlock have an anonymous union, which makes initializing it special
> for older compilers. By adding strategic brackets, it makes the build
> happy again.
>
> Fixes: 625e88be1f41 ("locking/qspinlock: Merge 'struct __qspinlock' into 'struct qspinlock'")
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
> diff --git a/include/asm-generic/qspinlock_types.h b/include/asm-generic/qspinlock_types.h
> index 0763f065b975..d10f1e7d6ba8 100644
> --- a/include/asm-generic/qspinlock_types.h
> +++ b/include/asm-generic/qspinlock_types.h
> @@ -63,7 +63,7 @@ typedef struct qspinlock {
>  /*
>   * Initializier
>   */
> -#define	__ARCH_SPIN_LOCK_UNLOCKED	{ .val = ATOMIC_INIT(0) }
> +#define	__ARCH_SPIN_LOCK_UNLOCKED	{ { .val = ATOMIC_INIT(0) } }
>  
>  /*
>   * Bitfields in the atomic value:

Acked-by: Waiman Long <longman@...hat.com>